Intercropping Perennial Fruit Trees and Annual Field Crops with Aromatic and Medicinal Plants (MAPs) in the Mediterranean Basin

Abstract

The Mediterranean basin (MB), a “climate hotspot”, is experiencing faster than average increases in global temperature and water deficit, as well as soil degradation, with detrimental impacts on food crop yield and pest/pathogen incidence. Hence, there is an urgent requisite for sustainable crop diversification strategies to promote crop resilience, soil quality conservation and pest/pathogen control. Intercropping is a strategy that has yet to be widely adopted. Presently, cereal–legume combinations represent the most common intercrops. Of relevance, a large number of medicinal and aromatic plants (MAPs), native to the MB, serve as potentially profitable indigenous resources for intercropping with food crops. Environmentally sustainable benefits of MB MAP intercropping with food crops have ironically been reported largely from research outside the MB. The present study aims to review the published literature from 2003 to 2023 on MAP intercropping with perennial nut/fruit crops and annual field crops in the MB. Published research is scarce but shows a promising upward trend, with 70% and 47% of intercropping studies with perennials and annual field crops, respectively, dated between 2020 and 2023. MAP intercropping shows potential in augmenting yield, pest/pathogen and weed control, soil health and cash crop quality, warranting further research with more widespread adoption in the MB.

1. Introduction

The Mediterranean basin (MB), coined a “climate change hotspot” [1], is experiencing a 25% faster than average increase in global temperatures coinciding with a predicted 30–40% reduction in precipitation, particularly in the southern portion of the MB [2,3]. Climate-related changes in the MB also involve increases in the frequency and severity of extreme weather events, including heat waves, dry spells, drought, unexpected flash floods and frost [4,5,6]. Given the environmental heterogeneity of the MB, climate-related events occur with differing magnitudes from one region to another [3,6,7]. Together with climate change, unsustainable agricultural management practices have rendered the MB more susceptible to physical (erosion and desertification), chemical (reduction in soil fertility) and biological (biodiversity loss) soil degradation processes [8], with knock-on effects on pest/pathogen and disease incidence [9,10,11,12]. Collectively, these multi-faceted challenges pose a major threat to both production yield and quality in the entire MB agricultural sector [5].

Focusing on perennial nut and fruit tree crops, there is no return in investment until several years after planting. Hence, climate change and non-sustainable management effects on phenology, physiological processes, disease–pest frequency, yield and product quality specifically represent major challenges to producers of this agricultural sector within the MB [9,10,13,14,15,16,17,18]. Important staple cereal and legume field crops in the region, intrinsically linked to food security, are similarly subject to yield fluctuations [19,20] and increasing pathogen/pest pressure [5,21,22,23]. The spread of broomrape (Orobanche spp.), a parasitic achlorophyllous herbaceous weed, also represents a major constraint to legume production in rainfed cropping systems of the MB and Middle East [24]. Hence, there is an urgent requisite to increase food crop resilience to climate change impacts, to shrink the agricultural carbon footprint of unsustainable management practices and to enhance soil and biodiversity conservation whilst guaranteeing crop yield, weed and pest/pathogen control. In response, various adaption strategies, including the selection of more resilient plant material, have been extensively covered in recent reviews and meta-analyses for perennial fruit and nut crops [13,16,17,25,26,27], including grapes [16,28,29,30,31], and for annual field crops [21,24,32].

Of the adaption strategies, crop diversification, defined as the increase in crop diversity through the implementation of practices such as crop rotations, cover crops and intercropping, represents an important approach for sustainable agricultural development [10,33]. Of interest to the present review is intercropping, the agronomic practice of simultaneously growing two or more crop species in the same field in close proximity for a considerable proportion of the growing season [34]. This practice promotes crop resilience, product stability and environmental security though agro-ecosystem benefits (soil quality conservation, biodiversity and pest control) and provides alternative products to increase farmer profitability [34,35,36,37]. Common intercropping typologies include, row intercropping (specific row patterns with varying row ratios), strip intercropping (cropping in wide strips to facilitate machine operations), alley intercropping (growing crops in-between trees and bushes), mixed intercropping (sowing two crops on one terrain with no distinct row arrangement) and relay intercropping (growing two or more crops simultaneously during part of the life cycle of each crop).

Throughout the history of agriculture, intercropping has been a key element of traditional, smallholder, farming systems, but has largely been neglected in both scientific-based research and industrialized production [35,36,38]. As such, intercropping has yet to be widely adopted [37]. From a scientometric analysis of global intercropping research between 1992 and 2020, a significant upward trend in research publications was evident from 2015 [34]. Cereal grain–legume combinations constitute the most common intercropping strategy in annual field crops, whereas in agroforestry systems, the intercropping of orchards with legumes, legume mixes, cereals and grasses is reported [26,34,35,37]. Intercropping with medicinal and aromatic plants (MAPs), as a climate change adaptation strategy, was not featured in the aforementioned meta-analyses or reviews for fruit and nut perennials or annual field crops. In a recent meta-analysis published specifically for Mediterranean climate regions in 2020 [26], only a single reference was made to the use of MAPs as an intercrop [39].

A large number of MAPs, comprising anise, basil, caper, caraway, chamomile, chive, coriander, cumin, dill, fennel, fenugreek, lavender, lemon balm, lemon grass, licorice, marigold, marjoram, mint, parsley, rosemary, saffron, sage and thyme, are native to the MB [40]. Sustainable agricultural advantages of MAP cultivation include, improved soil health (soil organic nitrogen and carbon, soil water content, microbial activity and biomass), bio-pesticide and bio-herbicide control by allelopathic secondary metabolites, adaptability to diverse ecological conditions, including semi-arid conditions, with an added advantage to farmer profitability (essentials oil with high economic value) [41,42,43,44,45]. The potential benefits of intercropping with MAPs have been highlighted from studies, conducted mostly on vegetable crops, which have been subject to various reviews [42,43,46,47]. From these latter reviews, as well as from emerging MAP intercropping studies widely available on internet search engines, environmentally sustainable benefits of native MB MAPs have ironically been published in countries that are predominantly located outside the MB, such as China, India and Iran (major producers of MAPs), as well as parts of Africa [43,45,47,48]. To address desirable sustainable agriculture policy objectives in the MB such as improvements to soil quality and biodiversity [6], as well as to take into consideration climate change and unsustainable management risks to the MB, the present study aims to review published literature from 2003 to 2023 on intercropping perennial nut and fruit crops, as well as annual field crops, with native MB MAPs within the MB. Scientific research on MAP intercropping with perennial fruit trees and annual field crops in the MB is shown to be extremely scarce and warrant attention. Nonetheless, where possible, the objective was to provide an overview of benefits from the intercropping of various selected crops and MAPs in land use efficiency (LUE, involving increased yields, economic returns and weed control), soil health (improved physical, chemical and biological properties), bio-control (pathogen/pest and improved fauna biodiversity in natural predator populations and ecosystem services) and product quality (improved yield quality).

2. Methods

Using GOOGLE SCHOLAR and SCIENCEDIRECT, a search was conducted separately for each of the most common MB MAPs (anise, basil, caper, caraway, chamomile, chive, coriander, cumin, dill, fennel, fenugreek, lavender, lemon balm, lemon grass, licorice, marigold, marjoram, mint, parsley, rosemary, saffron, sage, tarragon and thyme), always in conjunction with “intercropping”. Additional keywords that were entered included “Mediterranean”, “perennial nut crops” or “perennial fruit crops” or “field crops” or “medicinal and aromatic plants”. Inclusion factors were peer-reviewed published research of open-field studies, and research conducted in any of the 24 MB countries, namely Portugal, Spain, France, Monaco, Italy, Malta, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Albania, Greece, Türkiye, Cyprus, Syria, Lebanon, Israel, Jordan, Palestine, Egypt, Libya, Tunisia, Algeria and Morocco. Exclusion factors included laboratory and greenhouse trials (even if conducted in the MB) and work that was not published in the English language.

3. Past, Present and Future Impacts of Climate Change in the Mediterranean Basin

The MB lies in a transition zone between mid-latitude and sub-tropical atmospheric circulation regimes. As such, the MB is characterized by significant environmental and geographical gradients from north to south and east to west [5]. Using annual precipitation data combined with temperature minimums and maximums, Köppen established geographic climate zones in 1900 [49]. According to this climate classification, temperate hot dry summers (classified as Csa) and temperate warm dry summers (classified as Csb) were traditional hallmarks of the Mediterranean-type climate, of which the MB represents the largest surface area (60%) [49]. However, from the homogenization of meteorological data, dated back from AD 1500, a distinct increase in daily temperature and reduced precipitation has been evident in the MB over the last 60 years [50]. More specifically, a 0.5 °C increase in both global and MB temperatures was shown to occur between 1980–1990 compared to late 19th-century levels [3,5]. By 2020, this had escalated to unprecedented increases of 1.6 and 1.2 °C for the MB and global temperatures, respectively [5]. The main drivers are linked to anthropogenic forces that are specifically linked to energy demand and electricity generation, as well as to population growth since the 1960s [5]. Moreover, sea surface temperatures have similarly been rising over the last decades at a rate of about 0.4 °C, with mean annual temperatures exceeding 20 °C for much of the eastern and southeastern MB [5]. Currently, large regions of Spain, Türkiye, Greece, the MB islands, and coastal regions of Italy, Morocco, Tunisia and the Middle East are still classified as Köppen Mediterranean Csa and Csb. However, Libya and Egypt are presently largely hot arid steppe (BWh), whereas regions of Spain, Morocco, Tunisia, Libya, Sicily, Crete, Türkiye and the Middle East are hot arid desert (BSh) [51,52]. Future predictions (2071 to 2100) show increases specifically in hot arid steppe and hot arid desert, for North Africa, the Middle East, Türkiye and parts of Spain [52], all currently at the strongest risk for increases in heat wave intensity [5,53]. Although the overall amount of precipitation is predicted to decrease, particularly in Italy, Portugal, Spain, and parts of Greece and Türkiye, extreme rainstorms are expected to prevail in these northern MB countries. Aside from droughts, floods are and will likely remain the most dangerous meteorological hazards [5,53].

Approximately 40% of the Mediterranean agricultural production value is derived from four crops: grapes (14%), wheat, tomatoes, and olives (9% each), of which the three latter crops constitute about 90% of the total global supply [53]. Given the environmental heterogeneity of the MB, and the propensity of climate-related events occurring with differing magnitudes from one region to another [3,6,7], it is evident that intercropping experiments with MAPs must be optimized for each cultivation area.

4. Intercropping with Aromatic and Medicinal Plants (MAPs) in the Mediterranean Basin

A total of 37 articles were found on intercropping MAPs with either perennial fruit crops (17 articles) or annual field crops (20 articles). Of the 37 articles published, 20 were conducted in Egypt alone. Of the published articles on woody perennials, 71% of the research was conducted in the northern (European) MB, being represented predominantly by Spain (7 articles) and Italy (3 articles). For the field crops, 95% of the published articles were from research conducted in the southern MB, represented by Egypt (16 articles) and Tunisia (3 articles), respectively.

4.1. MAP Intercropping in Perennial Woody Nut and Fruit Crops

Perennial woody fruit and nut crops are among the most bio-diverse agricultural systems in the MB, and include a wide range of deciduous (almond, chestnut, hazelnut, pine nut, pistachio, pecan, walnut, grape, cherry, apple, apricot, peach, plum, pear, fig, persimmon and pomegranate) and evergreen (olive, date palm and citrus fruit) species. Deciduous and evergreen perennials can be further classified into climatic zones which include warm temperature to subtropical (pistachio, pecan, persimmon, fig, olive, citrus fruits and date palm) and temperate (warm to cool temperate, chestnut, almond, grape, peach, hazelnut, cherry, apple and pear).

Climate change and non-sustainable agricultural management practices impact various aspects of perennial cultivation. Phenology in perennial fruit and nut crops is driven by temperature which regulates dormancy periods. Endodormancy is induced under cold temperatures rendering the trees, bushes or vines cold hardy, and chilling units (the number varying between different species) are then employed by the plant to track the passage of time over winter. Upon the completion of the required chilling units, the plants enter ecodormancy (requiring species-specific levels of heat), necessary to resume growth and production which also coincides with increased sensitivity to colder temperatures [17,54]. Rising temperatures in the MB are currently compromising the chilling unit requirements, leading to developmental abnormalities affecting yield and quality specifically in the temperate tree crops [7,17,54]. Since fruit trees in the MB are often grown in marginal and unfertile lands with low levels of soil organic matter [13] and are also traditionally cultivated at a low plant density [25,39], increased temperatures combined with variable and unpredictable precipitation events (drought, flooding) have accelerated water erosion and worsened soil degradation [18,26]. Moreover, the implementation of non-sustainable agronomic practices such as tillage to remove weeds on exposed land between trees, as well as the use of chemical fertilizers have collectively contributed to anthropogenic greenhouse gas (GHG) emissions and reduced agro-ecosystem fauna services [10,13,26]. Reduced ecosystem services and climate change (more specifically rising temperatures) aggravate pest outbreaks, which are currently spreading in Mediterranean orchards [9,10].

Considering the diversity of nut and fruit crops cultivated in the MB, published research on intercropping with MAPs as a crop diversification strategy under field conditions within this region is particularly scarce and warrant attention as a new potential sustainable strategy. The research will be covered in the following subsections for deciduous perennials and evergreen perennials, respectively. However, given that among the deciduous fruit crops, grapes have the largest area and the highest economic importance globally [15], grape was reviewed in a separate subsection from the remaining deciduous perennials.

4.1.1. Deciduous Perennials (Almond, Pomegranate, Apple)

The only published articles for MAP intercropping with deciduous tree crops in the MB are for almond (Prunus dulcis [Miller] D.A. Webb; four articles), pomegranate (Punica granatum L.; one article) and apple (Malus domestica [Suckow] Borkh.; one article) (

Table 1. Improved economic, environmental and quality aspects of deciduous perennial cash crops (almond, pomegranate and apple) intercropped with aromatic and medicinal plants (MAPs) compared to the cash crop (or MAPs) in monoculture.

Deciduous Tree Crops	MAP Intercrops (Intercropping Type)	Country/ Agronomic Practices	Improved Land Use Efficiency (LUE); ↑ Cash Crop/MAP Yields; ↑ Economic Return; and ↑ Weed Control	Improved Soil Health ↑ Soil Organic C (SOC) + Org Matter/Minerals/Beneficial Organisms/C Sequestration ↓ Erosion, ↓ GHG	Bio-control ↓ Pests/Pathogens/Disease Symptoms; ↑ Natural Enemies (Parasitism and Predators)	Improved Quality of Cash/MAP Crop ↑ Nutritional/Functional Properties
Almond	Rosemary, Sage and Thyme (strip) [39]	Spain (rainfed, no tillage)	↓ almond yield offset by ↑ MAP oil yield: thyme and rosemary, res.	↓ erosion and nutrient losses: thyme, rosemary and sage, res.	No information provided	No information provided
Almond	Caper and Thyme (alley) [18,56,57]	Spain (rainfed, no tillage)	↑ LUE: ns almond yield, ↑ thyme oil [18,57]	↑ soil H2O + stability + aggregation: thyme and caper, res.; ↑ SOC and avail. macro-nutrients: thyme and caper, res. [18] ↑ SOC: thyme only; ↓ CO2: thyme + caper [56,57]; ↑ soil C balance: thyme and caper, res. [56]	No information provided	No information provided
Pomegranate	Basil and Rosemary (alley) [58]	Egypt (irrigated)	↑ LUE (1:4 plant ratio): rosemary and basil, res.; ↑ pomegranate yield	No information provided	No information provided	↑ Brix, anthocyanin content and ↓ abiotic injury of fruit ↑ volatile oils, volatile oil yield for both MAPs
Apple	Basil and Marigold (row) [59]	France (peri-urban and irrigated)	No information provided	No information provided	↑ parasitism of coddling moth, ns predators: basil only; ↓ pests + predators: marigold only. Ns for disease symptoms	No information provided

The most successful MAP is listed first followed by the remaining MAPs, respectively (res.), in descending order. A + sign is inserted between the respective MAPs where performance is equivalent. ↑ Denotes increases and ↓ denotes decreases.

). Almond cultivation in the Mediterranean basin is extensive. Spain represents the second largest global producer, with Morocco, Türkiye, Italy, Algeria and Tunisia all ranking within the top ten global producers for 2023 [55]. The articles on intercropping MAPs with almond trees were all performed in semi-arid rainfed regions of Spain, facing severe land degradation problems [18]. The first published article in 2008 was aimed at identifying the best soil management strategy, using non-tillage strip intercropping with rosemary, sage and thyme, compared to conventional tillage with no intercrops over a four-year period on hill slopes [39]. All MAPs selected were perennials, requiring much less maintenance and management practices after crop establishment than annuals. Thyme was shown to outperform rosemary, and more specifically sage, in significantly reducing runoff, annual soil loss as well as N, P, and K nutrient losses, even though all MAPs significantly improved the aforementioned parameters compared to the control. The denser morphology of thyme (also an evergreen), followed by rosemary, ensured better soil cover. Although, the almond yield was slightly lower when intercropped with the MAPs (attributable to water competition), almond losses could be completely offset economically by the gain in thyme and rosemary essential oil yields [39].

The sustainable benefits of thyme, compared with the performance of the evergreen perennial caper, were further investigated under no-tillage conditions over a two-year period (Table 1) [56,57]. Taking into account soil carbon fluxes (outputs and inputs), it was shown that thyme, followed by caper, significantly improved C balance [56]. Both thyme and caper were also significantly shown to reduce soil CO₂ emissions, related to no-till practices, whereas no N₂O emissions were observed due to the lack of chemical fertilization [57]. Only thyme, as an evergreen crop, was shown to improve soil organic carbon and moisture. The presence of thyme and caper alley crops had no effect on almond yield, but thyme essential oil yield improved the overall productivity of the agro-ecosystem in terms of LUE [57]. These results were corroborated by Almagro et al., 2023 [18]. After three years, both thyme and caper significantly improved both soil aggregate stability and water availability in the topsoil (at 0–10 cm depth), whereas only thyme improved those properties in the subsoil (10–30 cm depth). Mineral element content was improved by MAPs in both topsoil and subsoil [18]. Collectively, these results showed that, for almond cultivation, the use of the perennial evergreen MAPs (in this instance thyme) can significantly improve LUE and soil properties. What is yet lacking and warranting of research is the effect of these perennial MAPs as bio-control agents. Also warranting attention are MAP intercropping studies on other perennial fruit crops, especially nut crops which are completely lacking.

For pomegranate, sweet basil and rosemary were used as intercrops at different row ratios (1:1, 1:2 and 1:4 for pomegranate: MAP) over a two-year period in Egypt (Table 1) [58]. When intercropped, pomegranate fruit quality was significantly improved, with the best results evident for rosemary at a planting density of 1:3 and sweet basil at a planting density of 1:4. The combined yield advantage in terms of land equivalent ratio (LER), area time equivalent ratio (ATER) and LUE indices was the greatest for 1:4 for the rosemary, followed by 1:4 for the sweet basil intercropping pattern arrangement [58]. The sole focus of a one-year study conducted in a semi-urban field area in France was to investigate the biological control of the codling moth Cydia pomonella L. (a pest causing high damage to various perennial crops worldwide, particularly to apple orchards) by intercropping apple with sweet basil and French marigold (positioned in pots) [59]. Results of the study showed that intercropping with basil increased codling moth parasitism, but did not affect arthropod predator abundances, whereas intercropping with French marigold, decreased both pests and predators (Table 1). This paper highlights the requisite for more studies on field-cultivated crops intercropped with MAPs, selected as either attractants or repellents for specific pest or predator requirements in the cultivation area.

4.1.2. Deciduous Perennials (Grape)

Viticulture and wine making play a crucial role in the socio-economy of the MB, with Italy, Spain, Portugal and Greece jointly producing 38% of the global wine production [31]. Aside from wine production, overall grape (Vitis vinifera L.) production in the MB is extensive, with the leading countries, in descending order, being Italy, Spain, France, Türkiye, Egypt, Portugal, Greece, Algeria, Morocco, Syria, Tunisia, Croatia and Slovenia [60]. Lebanon, Jordan, Israel, Bosnia and Herzegovina, Palestine, Libya, Cyprus and Montenegro represented minor grape producers within the Mediterranean basin [60]. Collectively, climate change impacts specific for viticulture include the following aspects: vine phenology (advancing the date of bud break, flowering and véraison or onset of ripening), grape yield (impaired photosynthesis) and quality (decreasing anthocyanin content, aroma compounds and acidity), and pest and disease pressures (increasing parasitic plant nematodes and soil-borne fungal pathogens) [16,28,30,31]. Viticulture is also facing emerging challenges because of a social demand for environmentally friendly agricultural management, such as non-chemical pest management [30,31]. Given the projected risks to viticulture, there is a requisite for the implementation of timely, suitable and cost-effective adaption techniques/technologies which should be planned and tuned to local climatic conditions [26,31]. Since MAPs have not yet been considered as viable intercropping options for vineyards [61], published research for this agronomic sector is negligible, with only four articles published from studies conducted in the MB (

Table 2. Improved economic, environmental and quality aspects of grape crops intercropped with aromatic and medicinal plants (MAPs) compared to the grape crop in monoculture.

Grape Crops	MAP Intercrops (Intercropping Type)	Country/ Agronomic Practices	Improved Land Use Efficiency (LUE); ↑ Cash Crop/MAP Yields; ↑ Economic Return; and ↑ Weed Control	Improved Soil Health ↑ Soil Organic C (SOC) + Org Matter/Minerals/Beneficial Organisms/C Sequestration ↓ Erosion, ↓ GHG	Fauna Bio-Control ↓ Pests/Pathogens/Disease Symptoms; ↑ Natural Enemies (Parasitism and Predators)	Improved Quality of Cash/MAP Crop ↑ Nutritional/Functional Properties
Thompson seedless grapevines	Anise, Black Cumin, Fenugreek and Parsley (row) [62]	Egypt (irrigated)	↑ Grape yield: fenugreek, anise, parsley and cumin, res. ↑ economic return: fenugreek, cumin, parsley and cumin, res.	↑ OM: fenugreek and anise ↑ N, P and K: fenugreek, anise, parsley and cumin, res. ↑ microbes: fenugreek, anise, parsley and cumin, res.	No information provided	↑ sugars, Brix and acidity: fenugreek and anise, res.
Flame seedless grapevines	Garlic (row) [63]	Egypt (irrigated)	Ns effect on grape and garlic yield; ↑ LUE and ↑ economic return	No information provided	↓ Parasitic nematode infestation	Ns effect on Brix and anthocyanin of grape
Sangiovese; Trebbiano Romagnolo	Basil-Lemon- Balm-Sage; (row) [64] Sage (row) [65]	Italy (no irrigation + fertilization)	Ns effect on grape yield [60]	No information provided	No information provided	↑ Volatile organic compounds (VOCs) [60,61]

The most successful MAP is listed first followed by the remaining MAPs, respectively (res.) in descending order. A + sign is inserted between the respective MAPs where performance is equivalent. ↑ Denotes increases and ↓ denotes decreases.

).

To the best of our knowledge, the first study reporting multiple beneficial sustainable effects of intercropping grapevine (mature 12-year-old Thompson seedless grapevine) with different MAPs (anise, black cumin, fenugreek and parsley) was conducted over two successive seasons in Egypt [62] (Table 2). Grape yield was significantly higher for grapevines intercropped with fenugreek, anise, parsley and black cumin (in descending order) than in monoculture. Although the yield for all MAP crops intercropped with grape was lower, the estimated combined net profit (grape + MAP) was highest for fenugreek, followed by black cumin, parsley, and anise [62]. Grape quality was improved by intercropping with only fenugreek and anise [62]. Additionally, compared to grape in monoculture, both soil microbial count and activity (based on symbiotic associations with soil microbes) were higher for grape intercropped with fenugreek, followed by anise, parsley, and black cumin [62]. This paper clearly shows the enormous potential of MAP intercropping in viticulture. The legume MAP fenugreek was shown to not only provide the best benefits to soil health but also the best potential economic benefits to growers. The role of this MAP in insect pest control, therefore, warrants attention. Garlic was given consideration as a MAP in Egypt since utilization by the ancient Egyptians is widely reported, providing evidence of the early movement of garlic into the MB from the native origins in south-central Asia. The intercropping performance of garlic as a sustainable bio-control alternative to nematicides and chemical soil fumigants was evaluated using Flame Seedless grapevines (9-year-old cultivar) over two consecutive seasons in Egypt (Table 2). Garlic showed promise by significantly reducing the number of plant parasitic nematodes (PPNs), specifically Meloidogyne incognita which is considered the most destructive PPN [63]. This is relevant since PPNs on vines are increased by climate change [12]. Although intercropping with garlic had no effect on either grape yield or quality, the LER and LUE were significantly increased, showing that this combination is a viable sustainable management option [63].

Very recently in Italy (Table 2), intercropping grapevine with MAPS was shown as a potential enological practice to influence the accumulation of volatile organic compounds (VOCs) in grape berries that are considered neutral (“non-aromatic”) such as Sangiovese (the most cultivated red grape variety in Italy) and Trebbiano Romagnolo in the protected designation of origin “Romagna” [64,65]. The selection of basil, lemon balm and sage as an intercropping mixture was based on the richness in aromatic compounds such as linalool, citronellal, thujone and camphor and the high potential of these VOCs to be emitted into the environment. In fact, the MAP mixture enhanced Sangiovese berry concentration of C13-norisoprenoids, various phenols and aliphatic alcohols, thereby evidencing the absorption of VOCs by the vine plants, either through the leaves, berries or roots [64]. Interestingly, the MAPs in the vineyards also slowed down technological ripening [64]. This is favorable in the context of climate-induced temperature change which shifts the berry maturation phase to warmer periods in the summer, adversely affecting grape composition, in particular, with respect to aromatic compounds [28]. Similarly, intercropping Trebbiano Romagnolo with sage alone influenced VOCs in grape berries [65], providing exciting prospects towards improving wine quality. Intercropping with MAPs promises innovative future prospects for the viticulture sector. By extension this will also include environmentally sustainable benefits that as of yet remain to be determined.

4.1.3. Evergreen Perennials (Olive and Date Palm)

Together with wheat, both grape and olive (Olea europaea L.) are commonly referred to as the Mediterranean triad, being the traditional emblematic crops with immense cultural, economic and ecological importance [15]. Similar to grape, olive production in the MB is extensive [53], with the first nine top global producers being represented in descending order by Spain, Italy, Morocco, Türkiye, Greece, Egypt, Portugal, Tunisia and Algeria [66]. Producing less olive oil in the global rankings are Jordan, Libya, Israel, Palestine, Croatia, Cyprus, Macedonia and Slovenia [66]. Olive agroforestry is a traditional, sustainable practice involving the intercropping of predominantly cereals and legumes to increase farmer profitability as well as to enhance soil and biodiversity conservation [67]. Although agroforestry practices are minimal compared to olive in monoculture, little research has been conducted on the productivity of such systems, especially with MAPs as understory crops [68]. As such, only six articles to date have been published for the Mediterranean basin (Table 3).

In an earlier study conducted in Morocco, where intercropping olive with annuals (especially wheat and barley, food legumes and vegetables) dates back to antiquity, it was shown that olive yield was not compromised by intercropping with the MAP, coriander, whereas sowing distance (degree of shading) influenced coriander yield [69]. To improve land use efficiency and economic returns, the optimal distances for sowing annuals including MAPs are deemed essential [69]. In a more recent study conducted in an agroforestry system in Greece, the sole objective of intercropping olive with MAPs as understory crops was to ascertain the effect of fertilization and shading on the quality of MAP essential oils [68]. Both shading and fertilization of chamomile and anise, respectively, were shown to either increase or decrease various essential oil components, rich in the substances defined by commercial specifications [68]. No information on sustainable benefits to the agroforestry system was provided.

Three studies conducted in Spain [70,71,72] and a single study in Italy [73] aimed to investigate the environmental benefits of MAP intercropping with olive on soil properties and insect populations (Table 3). In a very complex study performed on hill slopes investigating the SOC stratification index (SR-COS), a mixture of saffron–lavandin intercropped with olive was shown to improve the formation of stable aggregates and the microbial and fauna communities of the soil on the back slopes, which provide protection against organic matter (OM) decomposition [70]. Using lavandin (hybrid cross between Lavandula angustifolia Mill. and Lavandula latifolia Medik.) and saffron (no tillage), it was shown that after four years the olive–saffron combination improved soil properties in terms of fertility (total N and soil organic carbon (SOC)), SOC sequestration and soil aggregation [71] compared to the no-tillage control. Although the olive–lavandin combination did not improve soil aggregation processes or structural stability and SOC sequestration, there were no severe losses as compared to the control [71]. To assess increases in entomological diversity [72], olive tree intercropping with lavandin, rosemary and lavender was performed. In addition to the above-mentioned pollinator attractant and insect repellent MAPs, beehives were also positioned in the orchards. Given that this is an ongoing project, only preliminary data were presented. In a single orchard, lavandin intercropping resulted in increased predator and parasitoid numbers of olive pests in the month of April 2022. It was predicted that the arthropod community structure would have changed over the following months after flowering [72]. Interestingly, the rosemary and lavender plots did not survive, clearly showing that the selection of MAPs requires a prior in-depth analysis of the local abiotic and biotic conditions [72], as climate change impacts in the MB may be very heterogeneous [7]. From a preliminary two-year study conducted in Sicily (Italy), sage, thyme and lemongrass intercropped with young olive trees guaranteed an almost full soil cover, reducing the need for weed management along the intra-rows (forming a hedge row) [73]. The MAPs also increased insect (predator and pollinator) richness without influencing olive tree growth [73]. Given the importance of olive cultivation in the MB, the environmental benefits of MAP intercropping in terms of LUE and economic returns warrant further research in this sector.

Egypt is the world’s largest producer of dates, with Algeria, Algeria and Tunisia, respectively, among the top producers in the Mediterranean basin [74]. The impact of intercropping three legumes, including fenugreek, as understory crops with Sewy date palms (Phoenix dactylifera L.) was conducted over two seasons in Egypt [75]. Although clover outperformed fenugreek, fenugreek intercropping was shown to significantly increase Sewy date palm yield, LER and gross profits on both crops, as well as improving date quality [75].

Table 3. Improved economic, environmental and quality aspects of evergreen perennial cash crops (olive and date palm) intercropped with aromatic and medicinal plants (MAPs) compared to the cash crop or MAP in monoculture.

Evergreen Tree Crops	MAP Intercrops (Intercropping Type)	Country/ Agronomic Practices	Improved Land Use Efficiency (LUE); ↑ Cash Crop/MAP Yields; ↑ Economic Return; and ↑ Weed Control	Improved Soil Health ↑ Soil Organic C (SOC) + Org Matter/Minerals/Beneficial Organisms/C Sequestration ↓ Erosion, ↓ GHG	Fauna Bio-Control ↓ Pests/Pathogens/Disease Symptoms; ↑Natural Enemies (Parasitism, Predators)	Improved Quality of Cash/MAP Crop ↑ Nutritional/Functional Properties
Olive	Coriander (alley, various distances) [69]	Morocco (rainfed, no tillage)	Ns effect on Olive yield: ↑ shading and ↓ coriander yield	No information provided	No information provided	No information provided
Olive	Anise and Chamomile (alley) [68]	Greece	Ns shading effect on MAP seed + oil yields: anise + chamomile	No information provided	No information provided	Shading ↑ or ↓ certain MAP oil components; no quality changes for both MAPs
Olive	Mix: Saffron-Lavandin (alley) [70]	Spain (rainfed, no tillage)	No information provided	↑ SOC stratification index: saffron–lavandin	No information provided	No information provided
Olive	Saffron and Lavandin [71]	Spain (rainfed, no tillage)	No information provided	↑ soil SOC stocks: saffron and lavandin, res.	No information provided	No information provided
Olive	Lavandin, Lavender and Rosemary (alley) [72]	Spain (rainfed, no tillage)	No information provided	No information provided	↑ Predator + parasitoid: lavandin, one orchard	No information provided
Olive	Lemongrass, Sage and Thyme (row) [73]	Italy (irrigated, min–no tillage)	↑ Weed control: lemongrass + sage. No effect on tree growth	No information provided	↑ Pollinators + predators: lemongrass + sage + thyme	No information provided
Date Palm	Fenugreek [75]	Egypt	↑ Date yield, Ns fenugreek forage yield, ↑ LER and ↑ net profit	No information provided	No information provided	↑ Date fruit weight, ↑ TSS, ↑ total sugars and ↓ tannins

The most successful MAP is listed first followed by the remaining MAPs, respectively (res.), in descending order. A + sign is inserted between the respective MAPs where performance is equivalent. ↑ Denotes increases and ↓ denotes decreases.

Table 3. Improved economic, environmental and quality aspects of evergreen perennial cash crops (olive and date palm) intercropped with aromatic and medicinal plants (MAPs) compared to the cash crop or MAP in monoculture.

Evergreen Tree Crops	MAP Intercrops (Intercropping Type)	Country/ Agronomic Practices	Improved Land Use Efficiency (LUE); ↑ Cash Crop/MAP Yields; ↑ Economic Return; and ↑ Weed Control	Improved Soil Health ↑ Soil Organic C (SOC) + Org Matter/Minerals/Beneficial Organisms/C Sequestration ↓ Erosion, ↓ GHG	Fauna Bio-Control ↓ Pests/Pathogens/Disease Symptoms; ↑Natural Enemies (Parasitism, Predators)	Improved Quality of Cash/MAP Crop ↑ Nutritional/Functional Properties
Olive	Coriander (alley, various distances) [69]	Morocco (rainfed, no tillage)	Ns effect on Olive yield: ↑ shading and ↓ coriander yield	No information provided	No information provided	No information provided
Olive	Anise and Chamomile (alley) [68]	Greece	Ns shading effect on MAP seed + oil yields: anise + chamomile	No information provided	No information provided	Shading ↑ or ↓ certain MAP oil components; no quality changes for both MAPs
Olive	Mix: Saffron-Lavandin (alley) [70]	Spain (rainfed, no tillage)	No information provided	↑ SOC stratification index: saffron–lavandin	No information provided	No information provided
Olive	Saffron and Lavandin [71]	Spain (rainfed, no tillage)	No information provided	↑ soil SOC stocks: saffron and lavandin, res.	No information provided	No information provided
Olive	Lavandin, Lavender and Rosemary (alley) [72]	Spain (rainfed, no tillage)	No information provided	No information provided	↑ Predator + parasitoid: lavandin, one orchard	No information provided
Olive	Lemongrass, Sage and Thyme (row) [73]	Italy (irrigated, min–no tillage)	↑ Weed control: lemongrass + sage. No effect on tree growth	No information provided	↑ Pollinators + predators: lemongrass + sage + thyme	No information provided
Date Palm	Fenugreek [75]	Egypt	↑ Date yield, Ns fenugreek forage yield, ↑ LER and ↑ net profit	No information provided	No information provided	↑ Date fruit weight, ↑ TSS, ↑ total sugars and ↓ tannins

The most successful MAP is listed first followed by the remaining MAPs, respectively (res.), in descending order. A + sign is inserted between the respective MAPs where performance is equivalent. ↑ Denotes increases and ↓ denotes decreases.

4.2. MAP Intercropping in Annual Field Crops

Field crops cultivated in the MB are very diverse and include the cereal crops with durum wheat, bread wheat and barley being the most cultivated cereal crops, traditionally grown under rainfed conditions [20,76]. Durum wheat represents around 6% of the total wheat cultivation but has an important economic and cultural relevance in the MB, where it represents a staple crop that is increasingly threatened by drought and insect pests [23]. Additional field grain crops produced in the MB include rye, oats and maize, rice, sorghum and triticale. Sunflower is the most widely cultivated oilseed crop, whilst industrial crops include rapeseed, cotton and tobacco. Alternative, innovative field crops introduced into the MB as contributions to climate change mitigation, in compliance with the EU (European Union) Green Deal objectives, include teff, quinoa, camelina, black cumin, chia, emmer and flax [77].

Dry legume pulses (lentils, chickpeas, peas and beans) are representative field crops that form the backbone of the Mediterranean agro-ecosystems from ancient times, yet the unique and broad biodiversity of legumes has not been sufficiently valorized in the MB [78]. Among the legume crops, faba bean (Vicia faba L., also known as faba bean or broad bean) represents an excellent, untapped, source of sustainable and quality dietary proteins, with potential as a functional food [79]. In Egypt, the faba bean represents an important source of food and feed protein but remains an underutilized crop in Western countries [79].

4.2.1. Cereal, Sugar and Non-Food Crops (Durum Wheat, Triticale, Maize, Sugar Beet and Cotton)

Only three published reports for cereal grain field crops reported in the MB were collectively centered on yield improvements (

Table 4. Improved economic, environmental and quality aspects of annual field cash crops (durum wheat, triticale, maize, sugar beet and cotton) intercropped with aromatic and medicinal plants (MAPs) compared to the cash crop in monoculture.

Field Cereal, Sugar and Non-Food Crops	MAP Intercrops (Intercropping Type)	Country/ Agronomic Practices	Improved Land Use Efficiency (LUE); ↑ Cash Crop/MAP Yields; ↑ Economic Return; and ↑ Weed Control	Improved Soil Health ↑ Soil Organic C (SOC) + Org Matter/Minerals/Beneficial Organisms/C Sequestration ↓ Erosion, ↓ GHG	Fauna Bio-Control ↓ Pests/Pathogens/Disease Symptoms; ↑ Natural Enemies (Parasitism and Predators)	Improved Quality of Cash/MAP Crop ↑ Nutritional/Functional Properties
Durum wheat	Fenugreek and Fenugreek–clover mix (inter-row) [80]	Tunisia rainfed	↑ Weed control: fenugreek–clover and fenugreek, res. ↑ Grain yield: fenugreek–clover and fenugreek, res.	↑ Soil moisture: fenugreek mix and fenugreek, res.	No information provided	↑ Grain quality (protein) fenugreek–clover and fenugreek, res.
Triticale	Fenugreek and Vetch + mix [81]	Tunisia rainfed	↑ LER, ↑ forage yield: vetch and fenugreek, res.	No information provided	No information provided	No information provided
Maize	Sweet Basil (row) [82]	Egypt	↑ LER (basil: maize 100:33) and ↑ gross income (basil: 100:25)	No information provided	No information provided	↓ Volatile basil oil in intercropping compared to basil alone
Sugar beet	Garlic (row, different distances) [83]	Egypt	↓ Sugar beet yield and ↑ gross return both crops at 25 cm and 50 cm distance	No information provided	↓ Tortoise beetle pest, cotton leaf worm and beet moth pests	Ns on sugar percentage and ↑ juice quality
Sugar beet	Fennel, Coriander, Dill and Marjoram (row) [84,85]	Egypt no pesticide use	↑ Sugar beet yield: fennel, dill, coriander and marjoram, res. [84]	No information provided	↓ Tortoise beetle coriander, fennel, dill and marjoram, res. [84] ↓ Cotton leaf worm: fennel, dill, coriander and marjoram, res. ↓ Sugar beet fly pests: dill, fennel, coriander and marjoram, res. [84] Predators: all but specific for each MAP [85]	↑ Sucrose: fennel, dill, coriander and marjoram, res. [84]
Cotton	Sweet Basil (Row: low + high basil density; 60 and 90 cm) [86]	Egypt irrigated and no pesticide use	↑ Cotton yield, ↑ LER: all except low density at 90 cm and ↑ gross income: low density at 60 cm is the best	No information provided	↓ Pink bollworm: high basil density at 60 cm. ↓ Spiny bollworm: low basil density at 90 cm. ↑ Arthropod and spider predators: 60 cm and 90 cm, res.	No information provided

The most successful MAP is listed first followed by the remaining MAPs, respectively (res.), in descending order. A + sign is inserted between the respective MAPs where performance is equivalent. ↑ Denotes increases and ↓ denotes decreases.

). In an experiment conducted in Tunisia in two locations (sub-humid and semi-arid), durum wheat (Triticum turgidum subsp. durum [Desf.] Husn.) was intercropped with a clover–fenugreek mix and singularly with the two species alone under different herbicide and/or N regimes [80]. Overall, although the clover–fenugreek mix outperformed fenugreek in improving wheat yield and grain protein content, a significant improvement was demonstrated with fenugreek alone compared to the sole wheat crop. The contribution of fenugreek biomass was instrumental in weed control and in preserving soil moisture in the semi-arid site. Both fenugreek alone and the fenugreek–clover mix impacted positively, compared to the wheat crop in monoculture [80]. Mixed intercropping is projected to be important in areas with low water and nutrient inputs where climate change will force larger areas to become forage systems [81]. To investigate the efficacy of mixed intercropping, fenugreek considered as a forage legume, was intercropped with triticale (X Triticosecale Wittm.) and compared to triticale–vetch intercropping in different seeding percentage mixes. Overall, results showed that, compared to the respective crops in monoculture, the mixtures improved crop yield regardless of the seeding percentage. However, vetch demonstrated a greater competitive ability to exploit resources in a mixture with triticale, compared to fenugreek [81]. For maize (Zea mays L.) intercropping, sweet basil was used in different percentage mixes with the objective of establishing both which maize cultivar and percentage seeding mix provided the best gross income and yield [81]. The highest LER was obtained with the Giza-2 variety when intercropped with basil (100% basil + 33% maize), and the highest gross income occurred at 100% basil + 25% Giza 2, even if the percentage of basil volatile oils was lower in intercropping [82].

Research on sugar beet (three articles) and the most widespread profitable non-food crop, cotton (one article), were primarily centered on insect pest bio-control and improved LUE (Table 4). Sugar beet (Beta vulgaris L.) is subject to numerous insect pests, and the three published papers in Egypt addressed the effects of intercropping with MAPs on selective pest populations and their respective natural predators [83,84,85]. Garlic was shown to significantly reduce larvae of the tortoise beetle (Cassida vittata Vill), beet moth (Scrobipalpa ocellatella Boyd) and the Egyptian cotton leafworm (Spodoptera littoralis Boisduval) over two seasons [83]. Although sugar beet yield was significantly lower with garlic intercropping, the gross income from the combined crops was higher at intercrop planting distances of 25 cm and 50 cm. In contrast, significantly increased sugar beet yield and quality (sugar percentage), associated with significantly reduced tortoise beetle infestations, were evident in sugar beet intercropped with fennel, followed by dill, coriander and marjoram [84]. Fennel and dill intercropped with sugar beet were also shown to be the most effective MAPs against cotton leafworm and the sugar beet fly [85]. Interestingly, fennel, dill, coriander and marjoram showed distinctive capacities in attracting different predator populations [85], evidencing the need for more field studies on interactions between MAPs and insect predators. In cotton (Gossypium barbadense L.), sweet basil was used as an intercrop in three different intercropping regimes (absent, low and high basil area fraction) and two row distances (60 and 90 cm). Intercropping improved LER and cotton yield, thereby improving cotton production both ecologically and economically (gross margin, highest at the low density and 60 cm row distance) [86]. Moreover, the basil-induced pest repellence served to reduce both pink (Pectinophora gossypiella Saunders) and spiny (Earias insulana Boisduval) bollworm numbers compared to cotton in monoculture. The highest density of 60 m was more effective against pink bollworm and in attracting more arthropod and spider predators to cotton plants [86].

4.2.2. Legume Field Crops (Lentil, Soybean and Faba Bean)

Damping-off and root rot, predominantly caused by the fungi, Rhizoctonia solani (Cooke) Wint. and Fusarium spp, are primarily responsible for disease-associated reductions in lentil (Lens esculenta Moench.) yield. In a study conducted in Egypt, it was shown that over two consecutive years, intercropping with anise, garlic and cumin (in descending order), significantly decreased dampening off and root rot disease in lentils compared to lentil as a sole crop [87] (

Table 5. Improved economic, environmental and quality aspects of annual legume cash crops (lentil, soybean and faba bean) intercropped with aromatic and medicinal plants (MAPs) compared to the cash crop in monoculture.

Field Legume Crops	MAP Intercrops (Intercropping Type)	Country/ Agronomic Practices	Improved Land Use Efficiency (LUE); ↑ Cash Crop/MAP Yields; ↑ Economic Return; and ↑ Weed Control	Improved Soil Health ↓ Soil Organic C (SOC) + Org Matter/Minerals/Beneficial Organisms/C Sequestration↓ Erosion, ↓ GHG	Fauna Bio-Control ↓ Pests/Pathogens/Disease Symptoms; ↑Natural Enemies (Parasitism and Predators)	Improved Quality of Cash/MAP Crop ↑ Nutritional/Functional Properties
Lentil	Anise, Cumin and Garlic (row) [87]	Egypt	↑ Lentil seed yield: garlic and anise, res.	No information provided	↓ Dampening off and root rot: anise, garlic and cumin, res.	No information provided
Soybean	Peppermint (row) [88]	Italy irrigated	No information provided	No information provided	No information provided	↑ Leaf yield and ↑ essential oil components of peppermint
Faba bean	Coriander (ridge row) [89]	Egypt no pesticide use	↑ Bean yield	No information provided	↓ Aphid numbers and ↑ ladybird and lacewing hoverfly predators	No information provided
Faba bean	Garlic (2 varieties row) [90]	Egypt	↑ Economic return: Balady garlic and Sids-40 garlic, res.	No information provided	↓ Aphid, leafhopper and whitefly infestation: Balady garlic and Sids-40 garlic, res.	No Information provided
Faba bean	Coriander and Fenugreek (ridge row, high + low density) [91]	Egypt no pesticide use	↑ Bean yield: only fenugreek, low density only	No information provided	↓ Aphid numbers: fenugreek and coriander, res.	No information provided
Faba bean	Anise (row, different densities) [92]	Egypt irrigated	↑ LUE: anise: faba bean, 1:1 and 1:2	No information provided	No information provided	No information provided
Faba bean	Fenugreek + mixes [93]	Egypt conducted in infested field	↓ Broomrape parasite emerged shoots	No information provided	No information provided	No information provided
Faba bean	Fenugreek (row) [94]	Egypt	Ns effects on broomrape infestation in farmer’s field: all intercrops	No information provided	No information provided	No information provided
Faba bean	Fenugreek (row) [95]	Egypt different row width + density combinations	↑ LER and ↑ economic return: 100% fenugreek, 100% faba bean in wide ridges and other combinations, res. ↓ Broomrape infestation: all combination treatments	↑ Soil phenol content: all combination treatments	No information provided	No information provided
Faba bean	Fenugreek (row) [96]	Egypt, +/-herbicide treatment	↓ Broomrape parasite: herbicide + fenugreek and fenugreek alone, res.	No information provided	No information provided	No information provided
Faba bean	Fenugreek, Garlic and Parsley (trap intercropping) [97]	Egypt comparisons made to herbicide applications	↑ Faba bean biological yield: fenugreek and garlic, res. ↓ Broomrape infestation: garlic + fenugreek and parsley, res.	No information provided	No information provided	No information provided
Faba Bean	Fenugreek and Garlic (row) [98]	Egypt fields naturally infested and comparison to herbicides	↑ LER ↑ economic return: garlic + AMF and fenugreek + AMF ↓ Broomrape infestation: fenugreek + AMF and garlic + AMF, res.	No information provided	↓ Dampening off and root rot: fenugreek + AMF and garlic + AMF, res.	No information provided
Faba bean	Fenugreek (inter-row) [99]	Tunisia rainfed	↑ Faba bean yield ↓ Broomrape parasite spikes	No information provided	No information provided	No information provided

The most successful MAP is listed first followed by the remaining MAPs, respectively (res.), in descending order. A + sign is inserted between the respective MAPs where performance is equivalent. ↑ Denotes increases and ↓ denotes decreases.

). Increased lentil yield compared to the sole crop was also evident for intercropping with garlic and anise, respectively [87]. In the case of peppermint–soybean intercropping, the cash crop was peppermint, and the presence of soybean was shown to improve N availability to the peppermint [88]. The yield and essential oil components of peppermint were significantly increased when intercropped. Although the aim of the study was not intended to evaluate soybean responses to peppermint intercropping, it was noted that soybean was less prone to pest attack and fruit set was unaffected, raising the interesting possibility of a soybean–peppermint combination as a sustainable practice for both crops [88].

Given the importance of the faba bean in the southern MB, 10 studies were conducted in Egypt. Faba bean is susceptible to aphids as a key pest (Aphis craccivora Koch), as well as to leafhopper (Emposca lybica De Berg) and whitefly (Bemisia tabaci Gennadius). Using five varieties of faba bean intercropped with coriander over two consecutive seasons, a significant reduction in aphid pest infestation was observed compared to faba bean in monoculture [89] (Table 5). The same was evident when intercropped with garlic [90] as well as with fenugreek, followed by coriander (each at low- and high-density intercrops) [91]. Moreover, predator populations, including lacewing, ladybirds and hover flies were significantly increased by intercropping with coriander [89] and garlic (with Balady garlic outperforming Sids-40 garlic) [90]. Faba bean yield increases and improved LUE were evident with coriander [89] and for anise at a density of 1:1 and 1:2 for anise to faba bean [92]. The faba bean yield was reduced when intercropped with garlic; however, the net economic return was higher due to higher garlic yields [90].

Faba bean is also widely reported as being very susceptible to the root-parasitic weed, broomrape (Orobanche spp.). Although several authors described fenugreek as a suitable crop for intercropping with legumes, to reduce the infection level of O. crenata, a lack of experimental data was highlighted [93]. In a field experiment conducted over a two-year period in Egypt, fenugreek was shown to significantly reduce crenate broomrape shoot emergence attributable to allelochemicals released by fenugreek roots that interfere with the parasitic life cycle at the level of germination [93] (Table 5). Interestingly, in a later study, it was shown that faba bean genotype effect was a key factor in the faba bean-O. crenata crop allelopathic effect [94]. Using fenugreek in different plant densities and ridge widths, it was shown that two rows of faba bean (100% of sole cropping) on both sides of a wide ridge (120 cm width) with four rows of fenugreek (100% of sole cropping) in the middle of the ridge, could be an integrated control strategy to increase faba bean productivity, land usage and economic return whilst reducing broomrape infestation [95].

The efficacy of fenugreek in significantly reducing crenate broomrape infestation on faba beans cultivated in Egypt was verified in further field experiments but in comparison to synthetic herbicide treatments [96,97,98]. The application of herbicides (either Imazapic or glyphosate, twice in the season) together with fenugreek–faba bean intercropping was shown to suppress broomrape [96]. In response to fenugreek or garlic intercropping, broomrape biomass and spike numbers were significantly reduced (comparable to the effect of a single glyphosate application alone). This was also associated with a significant increase in faba bean yield [97]. A second application of glyphosate alone exceeded the suppression of broomrape (89%) compared to that induced by garlic or fenugreek (73%) [97]. With the objective of introducing environmentally friendly alternatives to herbicides, arbuscular mycorrhiza fungi (AMF) and yeast as bio-control agents were used. The latter were compared to the chemical application of herbicides (glyphosate) and fungicides (Rizolex-T50) in controlling crenate broomrape weeds and fungal root diseases, respectively [98]. Intercropping with fenugreek followed by garlic (both integrated with AMF application), promoted crop growth and significantly enhanced seed yield/ha whilst significantly decreasing both broomrape infestation and root rot, compared to the untreated controls [98]. Interestingly, AMF integrated with either fenugreek or garlic, performed equally well in reducing broomrape infestation when compared to the glyphosate integrated with either fenugreek or garlic. This shows that AMF together with MAPs could effectively replace the use of glyphosate. Higher economic returns were evident from the faba bean–garlic combination than the faba bean–fenugreek combination [98]. For sustainable agriculture, bio-control agents are superior to synthetic herbicides and pesticides. This very recent paper provides an incentive for the use of natural products in conjunction with MAP intercropping towards eradicating weeds and pests. Fetid broomrape (Orobanche foetida Poir) is a devastating faba bean parasite in Tunisia, and intercropping fenugreek with both a susceptible (Badi) and resistant (Najeh) faba bean cultivar was shown to significantly reduce field O. foetida plant numbers, especially on Najeh, with a concomitant increase in bean yield [99].

5. Assessment of MAP Intercropping in the Mediterranean Basin for Perennial Fruit and Nut and Annual Field Crops

As a sustainable agricultural diversification strategy, intercropping has yet to be widely adopted [37]. From the articles presented, intercropping indigenous MB MAPs with woody perennial fruit and nut crops in the MB is a relatively new field of research, with 70% of the mere 17 peer-reviewed studies published between 2020 and 2023. Similar to woody perennials, published research on MAP intercropping with field crops in the MB is very scarce. Of the 16 articles published, 47% were published between 2020 and 2023.

Despite the scarcity of work, intercropping with MAPs in the MB shows exciting potential for the total of 22 different MAPs native to the MB (

Table 6. Number of article citations for the types of aromatic and medicinal plants (MAPs) intercropped with various perennial fruit tree crops and annual field crops in counties of the Mediterranean basin.

MAP Intercrop Common (Scientific) Name, Category	MAP Intercropped with:	Article Citations	Research Countries
Fenugreek (Trigonella foenum-graecum L.), Annual legume	Grape, Durum wheat, Triticale, Date palm and Faba bean	12 [62,75,80,81,91,93,94,95,96,97,98,99]	Egypt and Tunisia
Garlic (Allium sativum L.), Annual bush	Grape, Sugar beet, Lentil and Faba bean	6 [63,83,87,90,97,98]	Egypt
Coriander (Coriandrum sativum L.), Herbaceous annual herb	Olive, Sugar beet and Faba bean	5 [69,84,85,89,91]	Egypt and Morocco
Thyme (Thymus baeticus L. and T. hyemalis Lange), Evergreen perennial shrub	Almond and Olive	5 [18,39,56,57,73]	Spain, Italy
Sweet Basil (Ocimum basilicum L.), Herbaceous annual herb	Pomegranate, Apple, Grape Maize and Cotton	5 [58,59,64,82,86]	Egypt, France and Italy
Anise (Pimpinella anisum L.), Herbaceous annual herb	Grape, Olive, Lentil and Faba bean	4 [62,68,87,92]	Egypt and Greece
Sage (Salvia lavandulifolia L.), Evergreen perennial shrub	Almond, Grape and Olive	4 [39,64,65,73]	Spain, Italy and Egypt
Caper (Capparis spinosa L.), Evergreen perennial bush	Almond	3 [18,56,57]	Spain
Lavandin (Lavandula × intermedia Emeric ex Loisel.), Evergreen perennial shrub	Olive	3 [70,71,72]	Spain
Rosemary (Rosmarinus officinalis L.), Evergreen perennial shrub	Almond, Pomegranate and Olive	3 [39,58,72]	Spain and Egypt
Black cumin (Nigella sativa L.), Herbaceous annual herb	Grape and Lentil	2 [62,87]	Egypt
Dill (Anethum graveolens L.), Herbaceous annual herb	Sugar beet	2 [84,85]	Egypt
Fennel (Foeniculum vulgare L.), Deciduous perennial herb	Sugar beet	2 [84,85]	Egypt
Marjoram (Origanum majorana L.), Herbaceous annual herb	Sugar beet	2 [84,85]	Egypt
Parsley (Petroselinum sativum L.), Biennial herb	Grape and Faba bean	2 [62,97]	Egypt
Saffron (Crocus sativus L.), Deciduous perennial herb	Olive	2 [70,71]	Spain
Chamomile (Matricaria recutita L.), Herbaceous annual herb	Olive	1 [68]	Greece
Lavender (Lavandula angustifolia), Evergreen perennial shrub	Olive	1 [72]	Spain
Lemon balm (Melissa officinalis L.), bushy perennial herb	Grape	1 [64]	Italy
Lemongrass (Cymbopogon citratus L.), Evergreen perennial grass	Olive	1 [73]	Italy
Marigold (Tagetes patula L.), Annual bush	Apple	1 [59]	France
Peppermint (Mentha × piperita L.), Evergreen perennial herb	Soybean	1 [88]	Italy

). Intercropping with fenugreek as a legume choice was the most widely reported [62,75,80,81,91,93,94,95,96,97,98,99] and was also exclusive to the southern MB (Table 6). Collectively, the publications presented from research conducted in Egypt and Tunisia on annual field crops showed that fenugreek improved LUE in terms of combined yield and economic returns (cash crop + fenugreek (forage biomass or seed essential oils)). Improvements in weed control were also evident, specifically against broomrape for faba bean production (due to the secretion of allelopathic secondary metabolites), but also in general weed control in cereals (based on the biomass of fenugreek). From the studies on grape and cereals, improved soil health (water retention, increased mineral elements and microbial biomass) and cash crop quality was demonstrated. Interestingly, notwithstanding the great abundance of wild populations and local landraces in the MB, fenugreek is a neglected and underutilized species (NUS), despite the inherent potential both to survive in extreme conditions (adaptable to climate change) and to improve the yield of companion crops in intercropping systems through improvements in soil quality [100,101]. An urgent appeal has been made to introduce fenugreek in local agriculture [99]. Moreover, the medicinally important phytochemicals, contained in the leaves and seeds of this NUS MAP are important incentives for more extensive intercropping cultivation [101], especially in European and Middle Eastern MB countries, where to date there is no published information on the use of fenugreek as a legume intercrop choice. Garlic, the second most abundant MAP intercropping choice exclusive to the southern MB (Table 6), was similarly effective in improving LUE and potential economic returns, as well as in both insect pest and broomrape weed control [63,83,87,90,97,98].

Exciting prospects were also evident from thyme–almond intercropping. As a perennial evergreen, thyme (with less management input) ensured a better ground cover thereby improving soil properties and reducing erosion, simultaneously increasing LUE and potential economic return from a combined nut-essential oil harvest [18,39,56,57]. Thyme was also shown to improve fauna biodiversity in an olive grove [73]. Given that the secondary metabolite and essential oil content of thyme has pathogen/insecticidal properties [43,44], that are increased under drought stress [41], the bio-control and marketing potential of thyme as a perennial tree intercrop is warrant future study.

Anise, basil, fennel, lemon balm, marigold, marjoram, rosemary and sage are all representative MAPs with pathogen/pest bio-control properties [43,44], for which more studies on intercropping bio-control are warranted. Interestingly, the allelopathic secondary metabolites emitted by basil, sage and lemon balm were also shown to improve the VOCs in neutral (“non-aromatic”) grapevine varieties [64,65]. Aside from potential farmer profitability, sustainable environmental benefits of MAP intercropping in the viticulture sector present a new field of study with exciting future prospects [56]. Both sweet basil and coriander are NUS with insect control properties, hardiness to drought and sources of essential oils with high economic value [102,103], thereby also showing potential for exploitation as intercrops in the MB.

The majority of the MAPs have appeared in only one to three published articles, evidencing the scarcity of research on MAP intercropping with perennial fruit and annual field crops (Table 6). Given that the conservation and use of legume and nut species are of increasing national and regional importance in the MB [104], adaption diversification strategies such as intercropping warrant attention in view of climate change impacts. The same is evident for cereal crops, especially as the MB is among the few areas in the world where the climate is suitable for growing durum wheat [20]. Hence, it goes without saying that in these agricultural sectors, more extensive studies are required, not only on the aforementioned crops for sustainable benefits that have not yet been covered, but also in providing a greater representation of different perennial nut and fruit crops, as well as annual field crops, considering the species diversity cultivated in the MB. As an example, the MB (Spain, Türkiye, Egypt, Morocco, Italy, Greece, Israel and France as the highest producers, respectively) collectively contribute 20% of the world citrus production [105], yet there are no reports of intercropping MAPs with citrus crops within the MB.

Other than expanding on studies to cover a greater diversity of perennial and annual crops intercropped with MAPs, there are various additional “must do” research-based avenues requiring attention. Intercropping MAPs with trees and other crops is practiced traditionally in smallholder farming systems, with an existing knowledge base [35,36,38]. This is also evident from numerous sources of information published on the internet, suggesting which MAPs make the best companion plants for various fruit tree crops, for which published scientific knowledge is lagging. Hence, there is a need for a greater contribution of farmer knowledge in research and an exchange of information between farmers and researchers to bridge the gap between traditional knowledge and scientific-based research on MAP intercropping in the MB. Of the MB countries, Egypt is a forerunner in published MAP intercropping research, highlighting the evident collective scarcity of published research from the European and Middle Eastern MB countries. Since climate change impacts on the MB are very heterogeneous, and given the environmental heterogeneity of the MB, more widespread involvement by MB countries in MAP intercropping research is a prerequisite.

An additional “must do” requirement for MAP intercropping studies relates to the economic analysis, necessary for the adoption of MAP intercropping by farmers [37]. Although, all 37 articles showed environmental benefits focusing either singularly or collectively on aspects related to the soil health, weed control and pest control, only 9 articles (all conducted in Egypt) showed that the combined cash crop plus MAP intercrop provided higher monetary economic returns [58,62,63,75,82,83,86,90,95]. A further two articles [98,99] showed increased monetary economic return on the cash crop in fields infested with broomrape where fenugreek and garlic were cultivated with the sole purpose of weed control. Of the aforementioned articles, two presented costs related to the purchase of seed material and necessary cultural practices [62,86]. From research in Spain [18,39,57] and Tunisia [81], economic benefits were inferred (increased combined yields of cash crop + MAP crop) but not presented in monetary terms. Any economic profits can be offset by losses that may be incurred through unpredicted climatic events, increased labor costs when challenges arise in management (need for multiple harvests) and crop competition leading to reduced yields [37]. In a single paper, complete failure of two MAP crops were reported presumably due to abiotic factors [72], whereas unpublished studies similarly showed that rosemary and lavender (intercropped with almond in Spain) and lavender (intercropped with cherry trees in Spain and Greece) did not survive [106,107]. At present, it is not possible to objectively weigh up the benefits of MAP intercropping (weed, pathogen, insect pest control, relative yield and gross profitability) against the risks and barriers (troubleshooting site-specific complexities, climatic factors, challenges of managing multiple cultures and labor costs) [18,37,54]. Such an assessment can only be made once more extensive and long-term studies are made available. However, as a practice, intercropping can help reduce the risk of crop failure by diversifying the range of crops grown in the same field. Intercropping protects against crop failure or unstable market prices for a particular commodity, particularly in areas subject to extreme weather conditions such as frost, drought and flooding. If one crop fails, the other crops can still be harvested. It is especially suited for labor-intensive small farms since it offers more financial security than single-crop farming. The environmental effect of agriculture is minimized by intercropping since it necessitates less inputs in the form of fewer pesticide and fertilizer applications [108]. Moreover, by taking advantage of complementary resource use between different crops, intercropping can lead to higher crop yields. For example, reducing water loss and increasing soil moisture by allowing one crop to provide shade to the other. As growth resources such as water, nutrients, and light are more effectively absorbed and converted into plant biomass by the intercrop throughout time and space, yield advantage is also gained [108]. Overall, intercropping perennial fruit trees, annual field crops, and MAPs in the MB offers numerous benefits, including reduced pests and diseases, enhanced weed control, improved crop yields, elevated nutritional properties, increased mineral content and better soil health (Figure 1).

Regarding the immediate future, before initiating any study on MAP intercropping, the careful selection of the most appropriate MAPs as a secondary crop must be made, requiring preliminary assessments of local climate, soil conditions, crop nutrient requirements and pest/pathogen incidence [18]. The requisite for a prior in-depth analysis of the local abiotic and biotic conditions has been raised from failed studies [72,106,107]. Although the introduction of unexploited species of MAPs in cultivation schemes is presently receiving attention, the most suitable varieties and the environmental/cultivation practices for optimum yield and quality of MAPs remain largely unknown [109]. Aside from the environmental benefits of MAP cultivation, there is increasing interest in MAPs on the part of industry, agriculture and health sciences due to the significant biological properties of these plants [109], which potentially serve as an alternative source of income for growers.

To conclude, intercropping MAPs with perennial fruit and nut trees as well as annual field crops in the MB shows potential in augmenting yield, pest/pathogen and weed control, soil health and cash crop quality. This integrated approach holds great promise as a sustainable and efficient agricultural strategy in the region. For the successful adoption of MAPs in farming systems in the MB, more research is required to provide an objective analysis of economic profits/losses. Thereafter, collaboration between researchers and farmers will require effective planning to potentially minimize losses.