Almond Varietal Adaptation in Central Italy: Phenological, Ecophysiological and Agronomic Observations on Eight Cultivars of Commercial Interest

Abstract

Almond cultivation in the Mediterranean basin is driven by Spanish production, which has combined innovation in cultivation techniques with research on varietal improvement, releasing self-compatible and late-flowering varieties that are better suited to areas prone to spring frosts. The growing demand for almonds has also influenced the Italian nut market, pushing growers towards almond cultivation even in areas that historically have no full vocation due to certain climatic constraints, such as cold winters and spring frosts, which are now less severe and less frequent as a result of climate changes, such as along the Latium coastline in Central Italy. In this new regional context, an almond collection orchard was set up in late 2017 in the rural environment of the municipality of Tarquinia (province of Viterbo) to test the local adaptation of commercial almond cultivars. Phenological observations and data acquisition were conducted for three consecutive growing seasons (2022–2024) and referred to eight cultivars introduced in the orchard: namely Genco, Guara, Lauranne Avijour, Penta, Soleta, Supernova, Tuono, and Vialfas. Each accession was monitored for phenological and ecophysiological traits, plant vigor and yield, yield efficiency, and nut and kernel traits. The trial proved that Lauranne, Penta, and Vialfas, due to their late flowering, were able to avoid possible damage from the spring cold recorded in 2023, while Supernova, Penta, and Genco, with an average yield over the three-year period of 2.51 ± 1.53, 2.44 ± 1.07 and 2.69 ± 1.42 kg plant⁻¹, respectively, showed a higher average yield than the other cultivars tested.

1. Introduction

Around 30% of human nut consumption involves almonds (Prunus dulcis (Miller) D.A. Webb) [1]. Over the last ten years, its production has significantly increased, with the United States (California), Spain, and Australia currently standing out as the main almond-producing countries [2]. In Europe, with its long almond-growing tradition, mostly located in the southern regions as Apulia, Sicily, and Sardinia, Italy ranks as second largest almond producing country after Spain, where cultivation spans over 760,000 ha [3]. In Italy, almond cultivation covers a harvesting area of 53,900 ha, annually yielding on average about 74,500 tons of in-shell almonds, resulting in an average yield per hectare of 1.38 tons ha⁻¹ [2], including both traditional and newer specialized and intensive orchards.

Almond consumption has great dietary relevance due to its low sugar content (4–5 g 100 g⁻¹ of kernel) and its high content of fatty acids, proteins, minerals, vitamins, and phytochemicals, making it a healthy and nutritious foodstuff [4].

Almond kernels, the edible portion of almond fruit, are classified based on several characteristics, with key parameters for market and table consumption. They include technological traits, such as kernel size and shape, the kernel/nut weight ratio, and the occurrence of double kernel, the latter being considered a quality defect, particularly in the confectionery industry [5,6]. The technological traits of almond kernels are also important for managing and optimizing the production processes, as well as for identifying the optimal packaging solutions [4]. Furthermore, the mechanical properties of kernels depend on their chemical composition, and these traits may be affected by post-harvest operations, such as nut drying and storage [7]. Accordingly, several factors, including genotype, origin, growing conditions and processing steps, contribute to the final qualitative traits of the almond kernels. For instance, the level of mono- and polyunsaturated fatty acids, fibers, phytosterols, low amygdalin content in the kernel, and several essential vitamins and minerals in almonds, along with their potential impact on health benefits, are highly dependent on genetic endowment, environmental conditions, fruit ripeness, and both storage and processing conditions [8,9].

Based on the current steady increase in almond demand and evolving market trends, combined with the impacts of ongoing climate change, a worldwide expansion of almond cultivation driven by field trials is necessary to fully understand cultivar adaptation and profitability in new production areas [10,11]. Understanding almond cultivar adaptation in new growing areas is crucial not only for growers but for the almond industry, as it may drive innovation and efficiency in the almond production chain [12,13]. Indeed, successful almond cultivation largely relies on the strategic selection of cultivars capable of adapting to different environmental conditions and plant growing systems. Furthermore, the literature highlights the relevance of canopy management and light interception in maximizing the reproductive potential in almond orchards [14], as well as the role of different clonal rootstocks, which have demonstrated their impact on the vegetative development and overall growth performance of almond trees [15,16].

These findings underscore the need for tailored cultivar selection and suitable adaptation strategies to ensure optimal yield efficiency and profitability in almond farming. This is of great relevance in regions facing challenges, like water scarcity and climate variability, which can induce defoliation and tissue dehydration phenomena, reflecting in rapid plant decline [17,18]. The factors influencing almond cultivation profitability are multifaceted and include climatic traits and adaptation strategies. Temperature and sunlight exposure are crucial roles for almond flowering and fruit set, with mild winters and balanced rainfall followed by long and relatively hot summers being the most suitable conditions [3]. Furthermore, certain cultivars perform better in punctual environmental conditions. For instance, in Turkey, the Ferragnes cultivar exhibited higher nut and kernel weights in the Sebenoba area when compared to the same cultivar tested in the Karakose district, both areas located in the Turkish province of Hatay [10]. These results were confirmed by Llompart et al. [19], who found a high percentage of shelling and high kernel weight on the island of Mallorca (Spain), for the same cultivar.

Ongoing research and breeding programs are thus needed to develop the cultivars that are not only high yielding but are resilient to changing climate patterns. This includes breeding varieties capable of completing endodormancy under warmer and more variable climates [20], as well as those varieties with reduced susceptibility to chlorosis and enhanced resistance to pests and diseases [10].

Traditional Italian almond cultivation has historically relied on local varieties, often characterized by early or intermediate blooming, such as the self-compatible Italian cultivar Tuono [21]. The limited expansion of some local almond cultivars from Southern to Central Italy have been hindered by potential late-frost damage that may constrain the farm’s economical profitability.

Nevertheless, the current increasing trend in the Italian almond sector, coupled with climate changes affecting the Mediterranean basin, is pushing the introduction of almond cultivation into new areas. This expansion is also supported by the use of new rootstocks, which have allowed for cultivation in soils previously considered unsuitable and in regions where the climate may not be ideal. These developments highlight the need to enhance knowledge about plant adaptation, particularly concerning phenology, ecophysiology, and agronomic traits [22].

The aim of this study is to evaluate the phenological and agronomical performance of eight almond cultivars selected for their commercial value and late-flowering traits into the coastal area of Central Italy (Latium region), where almond cultivation is consistently increasing [23].

2. Materials and Methods

2.1. Experimental Site and Plant Materials

During autumn 2017, the Regional Agency for Innovation and Development of Agriculture in Latium (ARSIAL) had set up an almond germplasm collection located in Viterbo province (municipality of Tarquinia, Italy. Latitude 42°16′20″ N; longitude 11°42′26″ E; altitude 32 m a.s.l.), in a supposed reference area elected to introduce a new almond cultivation chain in Central Italy.

Eight cultivars, namely Genco, Guara, Lauranne Avijour (hereinafter Lauranne), Penta, Supernova, Soleta, Tuono and Vialfas, representing the first cluster of varieties introduced into the almond germplasm collection, and mainly characterized by late blooming flowers (

Table 1. Origins and main agronomical traits of the almond cultivars under investigation in the experimental field [26,27].

Cultivar	Origin	Plant Traits
Genco	Italy	Medium vigor, medium to late flowering, late ripening, medium-to-small fruit size, hard shell, kernel/nut weight ratio 30–35%
Guara	Spain	High vigor, medium-to-late flowering, early ripening, high fruit size, hard shell, kernel/nut weight ratio 35%
Lauranne Avijour	France	Medium-to-high vigor, late flowering, early ripening, medium fruit size, semi-hard shell, kernel/nut weight ratio 35–40%
Penta	Spain	Medium vigor, very late flowering, early ripening, medium fruit size, hard shell, kernel/nut weight ratio 30%
Soleta	Spain	High vigor, late flowering, late ripening, high fruit size, hard shell, kernel/nut ratio weight 30–35%
Supernova	Italy	High vigor, medium-to-late flowering, early ripening, medium fruit size, hard shell, kernel/nut weight ratio 35%
Tuono	Italy	High vigor, medium-to-late flowering, early ripening, high fruit size, hard shell, kernel/nut weight ratio 35%
Vialfas	Spain	Medium vigor, very late flowering, early ripening, medium fruit size, hard shell, kernel/nut weight ratio 25%

), were evaluated in the trial to assess their adaptation to the environment of the Latium coast. The Guara cultivar was reported to be genetically identical to the Tuono cultivar, which was confirmed by the DNA fingerprints performed using 35 microsatellite markers [24]. Similarly, in the Supernova cultivar, obtained by the irradiation of the early-flowering, self-incompatible Fascionello cultivar, nine microsatellite markers highlighted it as undistinguishable from Tuono, suggesting that Supernova originates from the latter [25]. Nevertheless, in nurseries and commercial orchards, the three accessions are currently marketed separately, which is why we have treated them as different cultivars.

The studied cultivars, each represented by three replicates arranged on the same row, were grafted onto rootstock GF677 (P. persica × P. dulcis) widely used in the local environment in stone fruit orchards due to its drought tolerance. The plants were spaced at 6 m × 5 m and were trained to a free vase system. The soil was classified as clay–loam texture, with a composition of 45.4% sand, 25.6% loam, and 30.0% clay. The soil also showed a sub-alkaline pH of 7.6, and contained approximately 2% organic matter, predominantly concentrated in the topsoil.

The almond orchard was managed with a natural green cover crop according to the guidelines of the Italian almond integrated production system. Soil fertilizer application included annual quantities of 120 kg ha⁻¹ N, 60 kg ha⁻¹ P₂O₅, and 60 kg ha⁻¹ K₂O. Each plant was drip irrigated, with a water supply of about 1500 m³ ha⁻¹ per growing season, depending on the seasonal rainfed and irrigation water availability.

The experimental field was in an area classified as Csa—hot-summer Mediterranean climate according to Koppen’s classification. This climate is characterized by hot and dry summer seasons, and wet winter with rainfall mainly caused by westerly winds. During the summer months, the average temperature reaches and exceeds 22 °C, whereas winter temperatures generally range between 0 to 18 °C.

Figure 1 reports the monthly rainfall and temperatures over the period 2022–2024, expressed as mean values, recorded by a weather station installed in the experimental farm. June was the warmest month, with an average maximum temperature of about 34.4 °C, while January, the coldest month, had an average minimum temperature of 3.7 °C.

During the investigation period, the average annual rainfall was approximately 475 mm. July was the driest month with 1.6 mm of mean rainfall, while October was the wettest, with a mean value of 82.5 mm.

2.2. Phenological Observations

Phenological traits of the tested cultivars were recorded weekly over the three consecutive growing seasons (2022–2024) through field-captured images. Observations were made according to the BBCH scale adapted for almonds [28], with a focus on three principal growth stages: stage 0 (sprouting time), stage 5 (inflorescence emergence), and stage 6 (flowering).

2.3. Chlorophyll, Flavonol, and Anthocyanin Leaf Content and Related Nitrogen Balance Index

During the 2024 growing season, ecophysiological leaf traits, such as chlorophyll, flavonol, and anthocyanin content, were measured using a digital leaf clip meter DUALEX PLUS^® (FORCE-A, Orsay, France) and expressed as µg cm⁻¹. The instrument also provides the nitrogen balance index (NBI), which is considered to be a valuable indicator of plant nitrogen status expressed as the ratio between chlorophyll and flavonol leaf content.

Field surveys were carried out over three different times during the growing season, in early June, early July, and late July, respectively. On each plant under evaluation, twenty full-expanded leaves were examined for a total of sixty leaves per cultivar and measurement date. To account for the effect of leaf orientation during field measurement, five sun-exposed leaves from each cardinal direction were selected for the measurements.

2.4. Trunk Cross Sectional Area, Plant Production, Yield Efficiency, Nut and Kernel Traits and Incidence of Double Kernels

At the end of each growing season, the trunk diameters were measured just above the grafting point (30 cm above the ground) to calculate the trunk cross-sectional area (TCSA), a robust indicator of plant vigor, expressed in cm².

To monitor the yearly plant production, in-shell almonds from all tested plants were manually harvested during each harvest of the examined growing season. The almonds were subsequently dried with a thermostatic heater (KW Apparecchi Scientifici srl, series W107TO, Siena, Italy) according to almond market guidelines (kernel moisture not exceeding 6% for both consumption and storage in shell), and then weighed with an electronic lab balance (Sartorius AG, Göttingen, Germany). Yearly plant production has been calculated as the mean value from the three replications per cultivar and expressed as kg plant⁻¹.

The ratio of yearly plant production and TCSA was also calculated in order to estimate yield efficiency (YE), expressed as kg cm⁻².

Furthermore, for each cultivar and research year, a nut sample of sixty in-shell almonds (twenty almonds per plant) was subjected to evaluation of the nut and kernel traits, assessing the nut, kernel, and shell weight (g), the kernel/nut weight ratio, and the incidence of double kernels, considered to be one of the most relevant commercial defects for this nut crop [16].

2.5. Statistical Analysis

The data recorded over the survey period were subjected to statistical analysis using RStudio software (version 2024.09.0+375). Before proceeding with the statistical approach, all the input data were tested through the Shapiro–Wilk test, in order to identify their distribution. In the presence of non-normal data distribution (p-value ≤ 0.05), a non-parametric approach was performed. Specifically, the Kruskal–Wallis test was applied to assess the effect of the factors “cultivar”, “year”, and their interaction on the traits analyzed, followed by Dunn’s test to determine the significance levels, considering a p-value ≤ 0.05. Values expressed as percentages were subjected to angle transformation according to the formula (x + 0.5)/2 before being analyzed, as this approach is widely applied in ecology and biological experiments to stabilize the variance and make the data more suitable for further statical analysis.

Leaf ecophysiological traits, recorded during the last research year, were subjected to an analysis of variance considering only the “cultivar” effect, whereas phenological observations were qualitative traits and therefore not subjected to statistical analysis.

3. Results

3.1. Blooming and Leafing Phenograms and Fruit Repining

The phenological stages of flowering of the eight cultivars studied over the three surveyed years are displayed in Figure 2. The blooming phase was defined as the period spanning from fertile bud opening, characterized by the emergence of the first floral organs still closed (orange histograms), to the end of flowering (blue histograms), which occurs when about 95% of the flowers were opened and showing browning of the stigmas. This phenological window generally extended from the second week of February to the first–second week of April for the later-flowering Penta and Vialfas cultivars, highlighting notable variability among the cultivars considered in this study.

The beginning of inflorescence emergence, marked by the swelling of the fertile buds and relative breakage of the perulae, generally occurs between the second week of February, for Genco and Guara in 2022 and for Tuono in 2023, and the second week of March, for Penta and Vialfas in 2023. As a result, the blooming period of these latter two cultivars, and partially for Lauranne, extends into the end of March–early April, unlike the other cultivars, which generally begin flowering earlier, in the first half of March.

In general, the average flowering period across all cultivars ranged from three to four weeks, with the Lauranne, Guara, and Supernova cultivars showing the shortest flowering phase at two weeks, in 2024; whereas, in 2022, Penta showed the longest blooming window, lasting four weeks.

Interestingly, an analysis of the annual phenological responses for each cultivar reveals the general trend for cultivars to anticipate flowering by one or two weeks between 2022 and 2024, with the only exception being for Genco, which showed greater stability, reaching the bloom stage during the beginning of March.

The leafing stage, defined as the period beginning with the vegetative bud burst (sprouting time) and continuing through the expansion and the development of leaves, was recorded between the third week of February and the second week of March, depending on the earliness of the cultivars. When comparing the initial vegetative (leafing) and reproductive (blooming) stages, most cultivars exhibited earlier inflorescence emergence. However, most cultivars showed an overlap of the beginning of sprouting time with flowering; whereas, in 2022, the cultivars tested, except for Genco and Guara, showed the start of sprouting time one week before flowering. Furthermore, Vialfas consistently deviated from this pattern, showing in 2023 and 2024 a vegetative onset that overlapped the breaking of the fertile buds (start of blooming); this was also the case for Guara, Lauranne, and Supernova in 2024.

The onset of fruit ripening, identified as the 1% incidence of almond hull split, was recorded in early August for Supernova, while Guara, Lauranne, Tuono, Vialfas, and Penta were also identified as the earliest accession, with the latter slightly later by a few days. By contrast, Genco and Soleta showed a delay in ripening of about 7–10 days compared to the other accessions.

On average, the ripening window lasted about three weeks in all accessions and research years, with a more gradual ripening recorded for Supernova.

3.2. Leaf Chlorophyll, Flavonol, and Anthocyanin Content and Nitrogen Balance Index

The box-and-whisker diagrams displayed in Figure 3 represent the distributions of the leaf chlorophyll content of the eight cultivars tested across the following survey dates in the 2024 growing season: 7 June, 4 July, and 24 July, for which a separate statistical analysis was applied for each survey date.

In general, the values recorded in the three seasonal surveys showed an increase in the variability of chlorophyll content among the different cultivars, reaching their maximum, expressed as the distance between maximum and minimum values, on the last date of investigation.

During the first survey, significant differences were recorded in the average chlorophyll content. Genco and Penta highlighted the highest values of 29.66 ± 4.95 and 29.07 ± 2.40 µg cm⁻², respectively, while Soleta and Tuono had the lowest detected values of 24.54 ± 1.84 and 25.44 ± 3.25 µg cm⁻², respectively. Similar observations emerged in early July, in which Penta, Genco, and Supernova showed the greater chlorophyll content of 30.55 ± 2.01, 29.05 ± 4.58, and 28.76 ± 2.76 µg cm⁻², respectively, higher than values recorded for Guara, Soleta, and Tuono, which showed a leaf chlorophyll content of 24.72 ± 3.35, 24.71 ± 4.58, and 24.36 ± 3.05 µg cm⁻², respectively.

During the third survey date (24 July) significant differences in chlorophyll content among the cultivars were observed. In Genco and Penta, high chlorophyll contents were detected, even though they were slightly lower in comparison to the previous survey dates (26.58 ± 3.06 and 25.42 ± 3.15 µg cm⁻², respectively). However, for the other accessions, a conspicuous reduction in average chlorophyll content was observed in late July, with the significantly lowest values recorded for Guara, Lauranne, Soleta, Supernova, and Tuono, ranging from 17.01 ± 2.90 and 19.06 ± 3.11 µg cm⁻².

Figure 4 displays the data for the distribution of flavonol content determined on the leaves of the eight almond cultivars under investigation. As already described for the chlorophyll analysis, the same statistical approach, based on a single date, was applied.

During the study period, the flavonol content trend showed a slight increase of the values during the measurement dates. In early June, Genco and Vialfas achieved the highest average values of flavonol content (2.26 ± 0.15 and 2.24 ± 0.07 µg cm⁻², respectively), which were significantly higher than the lowest values recorded for the Penta cultivar (2.08 ± 0.15 µg cm⁻²). In addition, truly interesting results were provided by the Genco cultivar, in which high uniformity in flavonol content was recorded, as evidenced by the very small size of its box-and-whisker scheme.

The output obtained from the other surveys (early July and at the end of July) partly confirms what was already recorded during the first time point. The significantly highest values were registered for the Vialfas and Soleta cultivars, reaching 2.28 ± 0.03 and 2.28 ± 0.10 µg cm⁻², respectively, in early July, with Vialfas presenting a fairly uniform distribution of data, as confirmed by the very small size of its box-and-whisker scheme in Figure 4. Otherwise, the significantly lowest values were identified for the Penta cultivar, amounting to about 2.2 µg cm⁻² in the last two survey dates.

Data distribution for anthocyanin content detected for the eight cultivars over the three survey dates are shown in Figure 5. Overall, it was noticeable that a progressive increase in the anthocyanin content for all the cultivars over the study period, reaching the highest concentrations in late July, when a greater heterogeneity in anthocyanin levels among the cultivars was found. At the beginning of June, the average anthocyanin content among the cultivars ranged between 0.11 ± 0.02 µg cm⁻², for Penta, and 0.14 ± 0.02 µg cm⁻², for Tuono, with no evidence of significant differences observed among all the accessions. In early July, Guara and Tuono showed the highest values of 0.16 ± 0.03 and 0.16 ± 0.03 µg cm⁻², respectively, which were significantly higher than those recorded for the Vialfas, Supernova, and Penta cultivars, ranging from 0.12 ± 0.02 to 0.13 ± 0.02 µg cm⁻². In the third survey date, the Guara and Soleta cultivars, with mean values of 0.24 µg cm⁻², showed the greatest anthocyanin content, significantly higher than those detected for Genco, Penta, and Vialfas, whose average values ranged between 0.15 ± 0.02 and 0.17 ± 0.03 µg cm⁻².

The NBI values recorded on the leaves of the eight cultivars tested during the study period are shown in Figure 6. Similar to the trend observed for chlorophyll content, the NBI values exhibit a pattern across the three survey dates, with a marked reduction observed during late July. For all three time points, significant differences were found among the cultivars analyzed. In addition, as the growing season progressed, an increase in the variability of the NBI values was observed. The NBI detected during the first observation ranged from 14.05 ± 1.58, for the Penta cultivar, to 11.29 ± 1.23, for the Soleta cultivar. Furthermore, the values recorded for Penta stood out as significantly higher than those observed for the Lauranne (11.40 ± 1.94), Soleta (11.29 ± 1.23), Tuono (11.79 ± 1.59), and Vialfas (11.8 ± 1.48) cultivars. A similar context was detected in early July, when the Penta (14.01 ± 1.09) cultivar showed the highest NBI values among the accessions, significantly higher than the Vialfas (12.00 ± 1.05), Lauranne (12.56 ± 2.70), Guara (11.04 ± 1.65), Soleta (10.87 ± 1.79), and Tuono (11.14 ± 1.47) cultivars. The latest survey demonstrated that the Genco and Guara cultivars, in addition to recording the highest average NBI values among all the cultivars analyzed, were distinguished by their greater trait constancy, since these cultivars showed reduced variation throughout the growing season, in contrast to the larger fluctuations observed in the other cultivars. Specifically, the NBI mean values for Genco and Guara stood at 11.73 ± 1.50 and 11.79 ± 1.51, respectively. Otherwise, the significantly lowest values were found for Supernova, Lauranne, Guara, Soleta, and Tuono, ranging from 7.91 ± 1.80 to 8.24 ± 1.34.

3.3. Plant Yield, Trunk Cross Sectional Area and Yield Efficiency

The plant production of in-shell almonds showed considerable variability among the three research years and was significantly affected by the year and by the interaction of cultivar × year, as shown in

Table 2. Plant yield (kg plant⁻¹), TCSA (cm⁻²), and YE (kg cm⁻²) of the eight cultivars tested during the three-year research 2022–2024. Data are represented as a mean ± standard deviation. Different lowercase letters on the columns indicate significant differences among pruning treatments (Dunn’s test, p ≤ 0.05). Note: *** was applied for p ≤ 0.001, and n.s. for not significant.

Cultivar	Year	Yield (kg Plant−1)	TCSA (cm−2)	Yield Efficiency (kg cm−2)
Genco	3-year average	2.69 ± 1.42	44.24 ± 5.75 ab	0.061 ± 0.033
Guara	3-year average	2.21 ± 1.47	39.51 ± 6.43 ac	0.062 ± 0.044
Lauranne	3-year average	1.85 ± 1.31	41.02 ± 8.25 abc	0.050 ± 0.036
Penta	3-year average	2.44 ± 1.07	46.30 ± 8.76 ab	0.057 ± 0.030
Soleta	3-year average	1.72 ± 0.90	50.69 ± 9.20 b	0.035 ± 0.020
Supernova	3-year average	2.51 ± 1.53	48.31 ± 11.57 ab	0.056 ± 0.040
Tuono	3-year average	1.93 ± 0.94	33.86 ± 4.71 c	0.060 ± 0.034
Vialfas	3-year average	1.60 ± 1.24	32.71 ± 5.94 c	0.052 ± 0.040
Average cvs.	2022	3.29 ± 0.79 a	37.10 ± 5.97 a	0.090 ± 0.021 a
Average cvs.	2023	1.73 ± 0.83 b	38.86 ± 7.05 a	0.047 ± 0.024 b
Average cvs.	2024	1.34 ± 1.13 b	50.27 ± 9.85 b	0.026 ± 0.021 c
Genco	2022	3.74 ± 0.13 ab	39.77 ± 1.07 abcd	0.094 ± 0.001 abc
Genco	2023	0.85 ± 0.05 cde	41.14 ± 0.61 abcd	0.021 ± 0.001 cdef
Genco	2024	3.47 ± 0.62 abc	51.80 ± 0.70 bd	0.067 ± 0.012 abcdef
Guara	2022	3.75 ± 0.07 ab	34.43 ± 1.09 ab	0.109 ± 0.002 a
Guara	2023	2.48 ± 0.10 abcde	36.68 ± 2.50 abcd	0.068 ± 0.006 abcdef
Guara	2024	0.40 ± 0.10 de	47.40 ± 3.75 abcd	0.025 ± 0.002 ef
Lauranne	2022	2.42 ± 0.51 abcde	35.60 ± 4.48 abcd	0.067 ± 0.008 abcdef
Lauranne	2023	2.92 ± 0.45 abcde	36.69 ± 1.54 abcd	0.079 ± 0.009 abcde
Lauranne	2024	0.21 ± 0.03 e	50.78 ± 5.88 bd	0.004 ± 0.001 f
Penta	2022	3.63 ± 0.16 ab	40.36 ± 2.27 abcd	0.090 ± 0.001 abcd
Penta	2023	2.30 ± 0.72 abcde	41.70 ± 2.39 abcd	0.055 ± 0.018 abcdef
Penta	2024	1.39 ± 0.43 abcde	56.85 ± 6.67 bd	0.025 ± 0.008 bcdef
Soleta	2022	2.46 ± 0.65 abcde	46.09 ± 3.87 abcd	0.053 ± 0.014 abcdef
Soleta	2023	0.75 ± 0.30 cde	49.86 ± 11.94 abcd	0.015 ± 0.006 def
Soleta	2024	1.95 ± 0.41 abcde	56.12 ± 10.19 bd	0.036 ± 0.011 abcdef
Supernova	2022	4.93 ± 0.28 a	40.65 ± 1.64 abcd	0.108 ± 0.003 a
Supernova	2023	1.18 ± 0.18 bcde	42.28 ± 1.75 abcd	0.028 ± 0.005 abcdef
Supernova	2024	1.97 ± 0.93 abcde	61.99 ± 10.30 cd	0.031 ± 0.013 abcdef
Tuono	2022	3.09 ± 0.37 abcd	30.51 ± 2.42 ac	0.102 ± 0.014 ab
Tuono	2023	1.60 ± 0.26 abcde	31.80 ± 0.88 a	0.050 ± 0.010 abcdef
Tuono	2024	1.10 ± 0.18 bcde	39.27 ± 3.88 abcd	0.028 ± 0.002 abcdef
Vialfas	2022	2.84 ± 0.59 abcde	29.41 ± 4.88 a	0.096 ± 0.010 abc
Vialfas	2023	1.73 ± 0.70 abcde	30.73 ± 1.67 a	0.056 ± 0.020 abcdef
Vialfas	2024	0.24 ± 0.06 e	37.97 ± 7.13 abcd	0.006 ± 0.001 ef
Source of variation
Cv		n.s.	***	n.s.
Year		***	***	***
Cv × Year		***	***	***

.

Overall, during the 2022 season, all the cultivars showed their highest plant yields, with the only exception of Lauranne, which achieved its peak production in the following growing season of 2023. The average yield of the cultivars tested in 2022 was 3.29 ± 0.79 kg plant⁻¹, resulting in a significantly higher yield than those recorded in the following years, characterized by average values of 1.73 ± 0.83 kg plant⁻¹ in 2023 and 1.34 ± 1.13 kg plant⁻¹ in 2024.

Although no significance emerged for this trait due to the effect of the cultivar, Genco stood out with the highest three-year average production values of 2.69 ± 1.42 kg plant⁻¹, in contrast to Vialfas, which recorded the lowest average plant yield (1.60 ± 1.24 kg plant⁻¹). Furthermore, Supernova stood out as the cultivar with the highest production in the 2022 season (4.39 ± 0.28 kg plant⁻¹). Notwithstanding, this cultivar showed a progressive yield decline in the following seasons, stabilizing at 1.97 ± 0.93 kg plant⁻¹ in 2024. Despite a significant reduction in yield during the 2023 season, Genco showed excellent performance in the 2022 and 2024 seasons, with mean yields of 3.74 ± 0.13 and 3.47 ± 0.62 kg plant⁻¹, respectively. On the contrary, the lowest production performance was recorded during 2024 for the Guara, Lauranne, and Vialfas cultivars, amounting to 0.40 ± 0.10, 0.21 ± 0.03, and 0.24 ± 0.06 kg plant⁻¹, respectively.

As reported in Table 2, the trait of plant vigor, calculated by the TCSA and recorded at the end of each growing season of the three-year research, was affected by the year, cultivar, and their interaction. As expected, the TCSA tended to increase year-by-year, showing a higher increase during the last study season, and reaching 50.27 ± 9.85 cm² on average. Moreover, in 2024, the Supernova, Soleta, and Penta cultivars were particularly notable for their vigor, reaching TCSA mean values of 61.99 ± 10.30, 56.12 ± 10.19, and 56.85 ± 6.77 cm², respectively. On the contrary, Tuono and Vialfas were characterized by more restrained vegetative development, recording the lowest TCSA values of 39.27 ± 3.88 and 37.97 ± 7.13 cm², respectively. In addition, when comparing TCSA values between the first and the last research year, the Supernova cultivar showed the largest percentage increase, amounting to +52.50%, compared with a smaller development recorded for the Soleta cultivar, characterized by a percentage increase of only +21.76%.

Yield efficiency was strongly affected by the year and by the cultivar × year interaction, though it was not influenced by the cultivar effect. Overall, the average YE values underwent a gradual decrease during the three-year research, recording the highest values during the 2022 season. This trend may be attributed to the seasonal increase of TCSA, which, however, was not accompanied by a corresponding increase in plant production. During the 2022 growing season, the highest YE values were recorded for the Guara (0.109 ± 0.002 kg cm⁻²) cultivar, followed by the Supernova (0.108 ± 0.003 kg cm⁻²) and Tuono (0.102 ± 0.014 kg cm⁻²) cultivars, suggesting how these cultivars were able to effectively use available resources to maximize production. On the contrary, Lauranne recorded the lowest values of 0.004 ± 0.001 kg cm⁻² for the 2024 growing season, whereas the YE declined over time for Vialfas.

3.4. Nut and Kernel Traits

Almond nut and kernel traits were affected by the year, cultivar, and their interaction, as shown in

Table 3. Nut weight, kernel and shell weight (g), and kernel/nut weight ratio (%) of the eight cultivars tested during the three research years. Data are represented as a mean ± standard deviation. Different lowercase letters on the columns indicate significant differences among pruning treatments (Dunn’s test, p ≤ 0.05). Note: *** was applied for p ≤ 0.001.

Cultivar	Year	Nut Weight (g)	Kernel Weight (g)	Shell Weight (g)	% Kernel
Genco	3-year average	4.41 ± 0.85 ab	1.29 ± 0.23 ab	3.12 ± 0.76 ab	28.89 ± 5.08 a
Guara	3-year average	4.53 ± 0.92 a	1.27 ± 0.41 ac	3.24 ± 0.66 a	28.27 ± 5.44 b
Lauranne	3-year average	4.15 ± 1.06 b	1.12 ± 0.32 d	3.03 ± 0.77 b	26.78 ± 2.73 b
Penta	3-year average	3.26 ± 0.63 c	0.88 ± 0.14 e	2.39 ± 0.57 c	27.44 ± 5.27 b
Soleta	3-year average	4.45 ± 1.09 ab	1.21 ± 0.18 c	3.23 ± 0.99 ab	28.29 ± 5.36 b
Supernova	3-year average	5.26 ± 1.01 d	1.33 ± 0.24 b	3.93 ± 0.92 de	25.26 ± 4.94 c
Tuono	3-year average	4.88 ± 0.82 e	1.24 ± 0.27 c	3.65 ± 0.66 d	25.35 ± 4.00 c
Vialfas	3-year average	5.19 ± 1.32 de	1.21 ± 0.30 c	4.08 ± 1.11 e	23.18 ± 3.78 d
Average cvs.	2022	4.23 ± 0.96 a	1.33 ± 0.31 a	2.90 ± 0.72 a	31.81 ± 3.73 a
Average cvs.	2023	4.53 ± 1.17 b	1.06 ± 0.28 b	3.47 ± 0.94 b	23.50 ± 2.98 b
Average cvs.	2024	4.83 ± 1.24 c	1.20 ± 0.27 c	3.63 ± 1.05 b	25.30 ± 3.93 c
Source of Variation
Cv		***	***	***	***
Year		***	***	***	***
Cv × Year		***	***	***	***

.

Over the three-year basis, Supernova and Vialfas showed the highest nut weights with average values of 5.26 ± 1.01 and 5.19 ± 1.32 g, respectively, significantly higher than those recorded for Penta, distinguished as the lowest cultivar for this trait (3.26 ± 0.63 g). Referring to yearly average nut weight across cultivars, a gradual increase was detected, from 4.23 ± 0.96 g, in 2022, to 4.83 ± 1.24 g, in 2024. Furthermore, significant differences were also observed from the analysis of the interaction cultivar × year, which underlines the variability of the cultivars across the years. Notably, the highest nut weight was recorded for Vialfas during the 2023 season, reaching an average value of 6.45 ± 1.19 g, followed by Supernova in both the 2023 and 2024 seasons, with average weights of 5.80 ± 0.70 and 5.74 ± 0.75 g, respectively. On the contrary, the lowest nut weights were found for Lauranne in 2023 (2.87 ± 0.35 g) and Penta in 2022 (2.78 ± 0.31 g).

The highest kernel weight values over the three-year research were found for the Supernova and Genco cultivars, with mean values of 1.33 ± 0.24 and 1.29 ± 0.23 g, respectively, while Penta showed the significantly lowest trait among all the cultivars tested, showing values of 0.88 ± 0.14 g. Referring to the trait expressed as the mean of the cultivars, the highest value was recorded in 2022, with mean values of 1.33 ± 0.31 g; whereas the lowest mean emerged in the 2023 growing season (mean values of 1.06 ± 0.28 g). As a whole, Penta appeared to be the most penalized cultivar for this trait, showing significantly lower weights in two of the three seasons analyzed, achieving 0.84 ± 0.15 in 2023 and 0.84 ± 0.16 in 2024. Nevertheless, the lowest value recorded during the entire study period was observed in 2023 for the Lauranne cultivar, with a mean weight of 0.73 ± 0.10 g. On the contrary, Guara showed the highest kernel weight in 2022, with a mean value of 1.64 ± 0.40.

Regarding shell weight, the average value over the three-year research was highest for Vialfas and Supernova, which achieved 4.08 ± 1.11 and 3.93 ± 0.92 g, respectively, while the lowest mean values of 2.39 ± 0.57 g were recorded by Penta. Considering the effect of the year, shell weights were significantly lowest in 2022 (2.90 ± 0.72 g), in comparison to those of 2023 (3.47 ± 0.94 g) and 2024 (3.63 ± 1.05 g). Overall, the highest shell weight was recorded for Vialfas in 2024, with mean values of 5.18 ± 0.97 g. Conversely, the lowest values were found for Penta in 2022 and Lauranne in 2023, standing at 1.84 ± 0.24 and 2.14 ± 0.28 g, respectively.

The kernel/nut weight ratio, considered to be one of the most relevant technological traits for market, highlighted a remarkable variability among the cultivars investigated. Genco had a higher significant kernel percent when considered as the mean of the three-research years, with values of 28.89 ± 5.08%, whereas the lowest mean values were recorded for Vialfas (23.18 ± 3.78%). The best kernel/nut weight ratio expressed as a mean of the cultivars was recorded during the 2022 growing season, with values of 31.81 ± 3.73%, while the lowest ratio was recorded in 2023 (23.50 ± 2.98%). In general, the Genco, Guara, Penta, and Soleta cultivars showed the significantly highest values in 2022, all exceeding 34%.

The incidence of the ‘double kernel’, one of the main defects for market [27], which is influenced by several factors, such as genotype, temperature before flowering and plant position in the orchard, was absent in the almonds tested during the 2022 growing season. In the following research years, Guara stood out with the highest double kernel incidence, achieving 8.33% in 2023 and 1.67% in 2024. In addition, in 2023, Tuono and Supernova recorded incidences of 3.33% and 5%, respectively.

4. Discussion

The almond tree needs a Mediterranean climate with slightly warm summers (30–35 °C) and cool winters and for its cultivation; deep, loamy, and well-drained soils are ideal, but medium soils may be suitable if supplemented with adequate irrigation [29]. Almond cultivation has undergone a steady expansion in recent years, often involving new areas whose soil and climate conditions remain largely unknown [30]. This expansion has been driven not only by increasing consumer demand, but by the recognition of the product’s high nutritional and nutraceutical value [31]. Its cultivation enlargement into unfamiliar environments has been facilitated using new rootstocks, which have made it possible to overcome those challenges associated with incomplete soil suitability [10].

The effects of climate change, such as rising average temperatures, are increasingly affecting the Mediterranean basin, considered to be highly vulnerable to global warming [32].

For these reasons, studies focused on the agronomic and physiological adaptation of the almond cultivars for new Italian growing areas are crucial in order to properly settle varietal choice and cultivation techniques in the new orchards [28].

As a temperate nut species, the almond tree is characterized by an early flowering stage which has limited its expansion in geographic regions where the risk of damage from late frost was effective [33].

In order to counteract this issue, some breeding programs have focused on releasing new self-compatible cultivars characterized by late or very late flowering able to reduce the risk of late frost damage [34,35].

Generally, most almond cultivars are characterized by a flowering stage that slightly anticipates leaf emission, due to the lower chilling and heat requirements of fertile buds compared to vegetative ones, as pointed out in the literature [33].

These phenomena also emerged in our study, where most of the cultivars analyzed showed inflorescence emergence slightly earlier than the sprouting time. However, a different condition was observed for the Vialfas cultivar, as leafing overlapped with the onset of flowering during the research years. Additionally, Lauranne showed yearly alternations between the flowering and vegetative phase, and Penta highlighted an early vegetative phase during the 2023 growing season and an overlap of leafing and flowering in the other two research years.

Referring to the flowering time, some authors [36,37] have detected a negative correlation between the earliness of flowering and its duration. However, this relationship was not always respected in our study, as in the case of the Tuono cultivar during the 2023 and 2024 seasons; although the full bloom was recorded in early March (one of the earliest), its time window, which extended for about two weeks, was found to be one of the shortest of the entire study.

Vialfas has been recently released as a late-flowering cultivar valuable both for market and fresh consumption [38]. It is able to escape late frosts without suffering damage and yield losses. This phenological behavior was also found in our study, in which Vialfas stood out as one of the later cultivars, along with Penta, with flowering recorded between the second half of March and the first week of April.

In general, the cultivars tested showed a slight variability in blooming over the years, probably influenced by seasonal climatic trends, as confirmed in the literature [39].

In almond trees, bearing, vigor, branching pattern, and yield are strongly influenced by the genotype as well as the soil and climatic conditions, orchard age, and agronomic management. Regarding yield per plant, some authors [40,41] have ranked several almond cultivars according to their performance, using a scale of 0 to 9. For instance, Guara was awarded with the highest yield (score of 9), while Vialfas was given a slightly lower value of 7.5. However, in our study Vialfas showed the lowest yield among all the cultivars tested, while Guara showed intermediate–high productivity. The lower yield for Guara observed in our study, compared to other findings [41], may be due to differences in the pedoclimatic conditions between sites, highlighting how cultivar yield performances are firmly influenced by site specificity.

The plant yields obtained in our study for Supernova, Lauranne, and Tuono were slightly lower than those observed for the same cultivars in the Sardinia region [42]. Nevertheless, Supernova stood out as having the second highest yield per plant in the trial, whereas Penta was distinguished for its good nut production, achieving 2.44 kg plant⁻¹ as the average value of the three-year research, which is in agreement with the literature for this cultivar [30].

The Soleta cultivar stood out for higher vigor, highlighted by the highest TCSA values. However, these results disagree with those recorded by Llompart et al. [19], in which the same cultivar was described to have a low vigor variety; whereas, for the Lauranne cultivar, an intermediate vigor was recorded, confirming what was observed by the same authors. Moreover, Penta stood out over the three-year research as a cultivar with high vigor, in slight disagreement with Dicenta et al. [30], who described it as having intermediate vigor. Vialfas, characterized by low TCSA values, as also reported in the literature [41], confirmed its aptitude for HD or SHD plantations.

Nut and kernel traits of the tested cultivars revealed outputs fairly in line with those reported in the literature [27].

Regarding kernel/nut weight ratio, all cultivars recorded average values below 30%, with Lauranne and Tuono reaching 26.78 and 25.35%, respectively. However, these findings were confirmed to be slightly lower than those reported in the literature [42,43], for which Lauranne, Supernova, and Tuono recorded kernel percent values of about 35%. The observed discrepancy in the kernel/nut weight ratio might be attributed to higher nut weights recorded in our study than those reported by Lovicu et al. [42], which resulted in a reduction in the kernel percent.

Chlorophyll, flavonols, and anthocyanins are metabolites that play crucial roles in the primary and secondary metabolism in plants [44]. Nitrogen availability, in turn, influences the content of flavonols, carbon-based secondary metabolites [45,46] which are generally inversely related to the chlorophyll content. In addition, a sensitive indicator of plant nitrogen status, known as NBI, is obtained from their ratio [47]. In our study, the increased flavonol and anthocyanin leaf content, mainly recorded in the last survey date (late July 2024), resulted in a reduction in leaf nitrogen content evidenced by the decrease in chlorophyll and NBI, as also confirmed in the literature [48].

Generally, high levels of chlorophyll and NBI are linked to increased plant productivity and reflect the plant’s more efficient nitrogen use and photosynthesis activity. This is the case for the Genco and Penta cultivars, which showed an interesting association between stable levels of chlorophyll, and NBI with high yields, unlike Supernova, where inferior levels of chlorophyll and NBI did not reflect increased productivity.

5. Conclusions

This study provides preliminary insights for establishing a new almond sector within a new environment that could hold great opportunities for its expansion, like the Latium coastline area. The three-year trial offers indicative data on the phenological, ecophysiological, and agronomical performance of some commercially relevant and late-blooming almond cultivars.

Specifically, the Penta and Vialfas cultivars were of great interest for their late flowering, a requested trait to avoid production losses due to late frosts, making them a valuable choice for growers settled in new cultivation areas. However, the tendency towards low-to-medium production, already observed in other experiments [38], remains to be verified for Vialfas in the local environment.

In terms of yield per plant, the best performances over the three-year research were observed in the Genco, Penta, and Supernova cultivars. However, it is important to note that both Penta and Supernova exhibited moderate-to-low kernel/nut weight ratios which could negatively impact the potential revenue for producers. Vialfas demonstrated the lowest vigor among all cultivars, making it a suitable choice for HD and SHD almond plantations [43], although its productive aptitude must be verified in depth. Furthermore, although Genco showed an intermediate–late flowering time, exposing the cultivar to potential frost damage in the punctual environment, it stood out for excellent environmental adaptation, especially when considering yield and ecophysiological performance.

The findings of our study, despite the lack of repeated measurement across multiple sites and long-term data, could open an interesting opportunity for further research to assess the almond cultivars potential. Moreover, focusing on the evaluation of different orchards management practices could provide valuable insights for growers, especially in terms of economic viability.