Horticulturae, Volume 5, Issue 4 (December 2019) – 14 articles

Climate change is increasing drought events and decreasing water availability. Tomato is commonly transplanted to an open field after seedling production in a nursery, requiring large volumes of water. Arbuscular mycorrhizal (AM) fungi help plants cope with drought stress; however, their effects depend on plant genotype and environmental conditions. In this study, we assessed the interactions among different tomato seedling genotypes and two AM fungi, Funneliformis mosseae and Rhizophagus intraradices, under two water regimes, full and reduced. Our results showed that F. mosseae was more effective than R. intraradices in the mitigation of drought stress both in old and modern genotypes. However, seedlings inoculated with R. intraradices recorded the highest values of leaf area. ‘Pearson’ and ‘Everton’ genotypes inoculated with F. mosseae recorded the highest values of root, leaf, and total dry weights under reduced and full irrigation regimes, respectively. In addition, ‘Pearson’ and ‘H3402’ genotypes inoculated with F. mosseae under a reduced irrigation regime displayed high values of water use efficiency. Our results highlight the importance of using AM fungi to mitigate drought stress in nursery production of tomato seedlings. However, the development of ad hoc AM fungal formulations, which consider genotype x AM fungi interactions, is fundamental for achieving the best agronomic performances. Full article

The bacterial wilt pathogen (Ralstonia solanacearum) is a highly pathogenic soil-borne bacterium that invades the vascular system of a host plant leading to plant wilting and death. In agricultural systems, tolerant rootstocks are usually used to enhance disease resistance and tolerance in crop plants to soil-borne pathogens. Here, two distinct eggplant cultivars with different tolerances to R. solanacearum infection, the disease-tolerant cultivar ‘S21′ and the disease-susceptible cultivar ‘Rf’, were used to investigate if scion tolerance level can affect tolerance of rootstock upon an infection of the same pathogen. Three scion/rootstock grafted combinations were considered: Rf/S21, S21/S21, and Rf/Rf. Plants that resulted from the combination Rf/S21, composed of the susceptible scion grafts, showed weak tolerance to R. solanacearum infection, and exhibited the poorest growth compared to the tolerant scion grafts (S21/S21). As expected, the combination Rf/Rf showed the lowest level of disease tolerance. Furthermore, a high level of exopolysaccharides (EPSs) and cell wall degrading enzymes (CWDEs) were detected in susceptible scion grafts. These factors are involved in plant growth inhibition due to blocking transport between scion and rootstock and damage of vascular tissues in the plant. A high level of reactive oxygen species (ROS) and active oxygen scavenging enzymes were also detected in susceptible scion grafts. Excess accumulation of these substances harms the dynamic balance in plant vascular systems. These results indicated that the use of a susceptible scion in scion/rootstock eggplant grafts contributed to a reduction in rootstock tolerance to Ralstonia solanacearum. Full article

Knowledge of carbon (C) and nitrogen (N) dynamics under different irrigation practices in pomegranate orchards is novel and essential to develop sustainable production systems. The aim of this research was to determine the effect of high-frequency drip irrigation and different rates of N fertilizer on C and N distribution in the soil and N uptake by pomegranate fruit and leaves. The main treatments were surface drip irrigation (DI) and subsurface drip irrigation (SDI), and the sub-treatments used were three initial N rates (N1, N2, and N3). As trees grew larger, the N application rate increased. From 2013–2015, trees received the following rates of N: 62–113 (N1), 166–263 (N2), or 244–342 kg/ha (N3). Soil and leaf total C (TC) and N (TN), soil dissolved organic C (DOC), soil nitrate (NO₃⁻), and total N uptake by fruit were evaluated between 2012 and 2015. Soil samples were collected to 120 cm depth at 15 cm increments. DI resulted in higher concentrations of TN, TC, NO₃⁻, and DOC in the upper 75 cm depth than SDI. The N3 treatment resulted in higher concentrations of TN, TC, NO₃⁻, and DOC under both DI and SDI. Neither DI nor SDI at the N1 or N2 levels increased TN and NO₃⁻ concentrations at 105–120 cm soil depth, indicating reduced leaching risk using high-frequency drip irrigation. Higher N uptake by fruit was observed in SDI than in DI in 2014 and 2015, and in N2 and N3 treatments compared with N1 in 2013 and 2014. The data indicate that the application rate at 166–263 kg/ha (N2) provided sufficient N for a 4–6-year-old pomegranate orchard and that high-frequency SDI is a promising technology for achieving higher N use efficiency and minimizing leaching loss of NO₃⁻ and DOC. Full article

Phalaenopsis orchid has become one of the most important potted plants in flower markets. However, the timing at which flowers reach the saleable stage can be very important since the demand may be larger for specific holidays. The regulation of stem growth could serve as an opportunity for regulation of flowering. The purpose of this study was to evaluate the effect of temperature on stem elongation. In this study, a stem elongation model established by a statistical technique was used to evaluate the effect of temperature. The stem lengths of four named Phalaenopsi varieties and 15 unnamed Phalaenopsi hybrids were measured under different temperature regimes. The three parameters of the logistic growth model, the maximum stem length, growth rate, and inflection point at which the growth rate reached a maximum value were estimated by using nonlinear regression analysis. Then, the differences among varieties in these three parameters were assessed by categorical testing. The results of this study indicated that stem growth rate was positively affected only by day temperature. The maximum stem length was negatively affected by the day temperature and positively influenced by the temperature difference between day and night. The results of this study could provide a practical method to regulate stem elongation by adjusting the temperatures, thus helping growers time the flowering of their potted orchids to meet market demand. Full article

This study evaluated the effect of antioxidant application on quality and physiological aspects of minimally-processed escarole (Cichorium endivia var. latifolia L.) stored at 0 °C and 90–95% relative humidity for 21 d. After minimal processing, leaves were immersed for 5 min in the following solutions: deionized water-control (CT), 1% ascorbic acid (AA), 1% citric acid (CA), 1% oxalic acid (OA), and 2% ethylenediamine-tetraacetic acid (EDTA). Excess water was removed and they were then packed in trays of expanded polystyrene and stored at 0 °C and 90–95% relative humidity for 21 d. Analyses were performed on day 0, after 1 h of processing, and then at intervals of 3 d. The 1% CA treatment maintained the highest levels of endogenous ascorbic acid and pigment content, as well as the lowest values of weight loss and Browning Index (BI). Microbiological development was within the limits established during storage for all treatments. Total phenolic compound content and the activity of polyphenol oxidase and peroxidase enzymes showed variations among treatments. Observing all results, it was concluded that 1% CA was the best antioxidant for the maintenance of the quality attributes of minimally-processed escarole for up to 21 d in cold storage at 0 °C. Full article

The Fiji Islands, like many small Pacific island nations, are thought to incur high rates of postharvest loss. Little work has been undertaken to quantify the amount of loss within Pacific horticultural value chains, or identify the key determinants. This study sought to quantify postharvest loss within Fijian smallholder tomato value chains and to examine the relative importance of current on-farm practices as possible contributors to this loss. A semi-structured survey of 115 smallholder tomato farmers in Sigatoka Valley and eastern Viti Levu was undertaken, covering socio-economic and demographic parameters, production and postharvest handling practice, and postharvest loss based on farmer recall. On-farm postharvest loss for smallholder farmer tomato value chains was between 26.1% in Sigatoka Valley and 27.6% in eastern Viti Levu. This finding was consistent with quantification of postharvest loss in Fijian tomato chains by direct determination, but is relatively high when compared to smallholder tomato value chain loss in Sub-Saharan Africa. When Fijian tomato value chains were segregated according to specific postharvest handling practice, the contributors to postharvest loss were often associated with on-farm decision-making. Those value chains that only harvested once a week, or in the early morning (before 7 am) or mid-day onwards, stored harvest product in the field for more than three hours, did not sort or grade prior to on-farm ripening, or used packing sheds that had relatively open designs, all had consistently higher levels of postharvest loss. The prevalence of specific postharvest handling practice in both locations is further reported. While this study highlights the impact of current on-farm postharvest handling practices on tomato value chain loss, what remain unclear are the underlying drivers associated with current postharvest handling behaviour and the decision-making that shapes quality and logistic control activities. Full article

Vertical farming is one of the suggested avenues for producing food for the growing world population. Concentrating the cultivation of crops such as herbs in large indoor farms makes food production susceptible to technical, biological or other problems that might destroy large amounts of food at once. Thus, there is a trend towards locally, self-sufficient food production in vertical systems on a small scale. Our study examined whether conventional knitted fabrics, such as patches of worn jackets, can be used for hydroponics instead of the specialized nonwoven materials used in large-scale indoor systems. To this end, seed germination and seedling growth of 14 different crop plant species on knitted fabrics with three different stitch sizes were compared. Our results showed that hydroponic culture on knitted fabrics are indeed possible and allow for growing a broad spectrum of plant species, suggesting recycling of old textile fabrics for this purpose. Among the 14 plant species studied, differences in germination success, average fresh and dry masses, as well as water contents were found, but these parameters were not affected by knitted fabric stitch size. Full article

A greenhouse research study was conducted at Eastern New Mexico University, Portales, NM, USA, in 2019 to examine the effects of different nutrient solutions on the growth and weight of two lettuce cultivars grown in a floating hydroponic system. Two lettuce cultivars, Buttercrunch and Black Seeded Simpson, were subjected to one of four different nutrient concentrations of N, K and Ca at 150, 100, and 150 ppm (N1), 210, 235, and 200 ppm (N2), 250, 300 and 250 ppm (N3), and 300, 350, and 350 ppm (N4), respectively. The Buttercrunch cultivar and N3 treatment proved significantly more productive than the other cultivar/treatment combinations. The greatest fresh weights were recorded in the N3 nutrient solution, 115.33 and 93.17 g/plant for Buttercrunch and Black Seeded Simpson, respectively. Buttercrunch had the greatest fresh weight, leaf number, and leaf and root length in all nutrient solutions. The nitrogen content of the solutions showed a significant positive relationship with chlorophyll content for both cultivars. It is expected that the development of a cheap and easy-to-use hydroponic system will help growers produce high-quality organic vegetables including lettuce. Full article

Datasets containing information on seed size have been published and are currently available. Nevertheless, there is a lack in the literature of a dataset dedicated to seed shape. We present a preliminary version for a dataset on seed morphology based on a comparison of seed shape with geometric figures. Similarity of the outline of seed images with geometric models is considered as a basis to classify seeds according to the geometric figures they resemble (e.g., ellipse, oval, cardioid). This allows, first, the classification of plant species according to their geometric type of seed, and second, seed shape quantification. For each seed image, the percent of similarity of their outline with a geometric figure can be calculated as a J index. Similarity in absolute terms is considered only when the J index >90. This criterion is important to avoid ambiguity and increase discrimination. The dataset opens the possibility of studying the relationship between seed shape and other variables such as seed size, genome complexity, life form or adaptive responses. Full article

Nineteen amides (three of them unpublished) were synthesized and tested on Tuta absoluta Meyrick (Lepidoptera: Gelechiidae), an important pest of Solanaceae plants worldwide. Three of these compounds (14, 15 and 16) presented high acute toxicity toward the pest, with LD₅₀s of 3.68 (CI₉₅ = 2.83 − 4.47), 6.46 (CI₉₅ = 5.85 − 7.20), and 13.52 μg/mg (CI₉₅ = 11.06 − 15.95), respectively. Amide 14 presented the fastest action (LT₅₀ = 1.2 minutes, CI₉₅ = 1.03 − 1.37), followed by amide 16 (LT₅₀ = 18 minutes, CI₉₅ = 9.96 − 26.04), and amide 15 (LT₅₀ = 3.7 hours, CI₉₅ = 0.69 − 6.71). When applied at a sublethal dose, they did not affect weight gain and leaf consumption of the pest. Bioassays were also conducted using the ant Solenopsis saevissima (Hymenoptera: Formicidae) and wasp Polybia ignobilis (Hymenoptera: Vespidae) to assess the toxicity of the amides against T. absoluta predators. Amides 14, 15, and 16 were harmless to S. saevissima but presented high toxicity toward P. ignobilis. Amides 14, 15 and 16 are potential hit compounds for the development of insecticides for T. absoluta control. However, their use should be carried out following the principles of ecological selectivity to mitigate potential adverse effects on non-target organisms. Full article

Grape (Vitis vinifera L.) marc has long been utilized as a compost feedstock. However, this process takes an extended period of time due to the phytotoxic chemical composition of the marc. Removal of these compounds presents an opportunity to utilize the grape marc as a growing medium. Following a water-based extraction procedure to remove polyphenolic compounds of interest, analysis of the depleted marc showed a decrease in the content of these compounds, and in nutrient and trace element levels. Carrot (Daucus carota L.) and corn (Zea mays L.) seedling emergence in the depleted marc and blends with compost were not adversely affected, demonstrating its effectiveness for growing plants at all ratios. A 50:50 blend of compost and depleted grape marc resulted in plant growth equivalent to the compost alone. This combined with the observed water holding capacity suggests that depleted grape marc, when blended with compost, can be a suitable alternative to peat or coconut coir for seedlings. Full article

Association between auxins and plant growth-promoting bacteria can stimulate root growth and development of fruit crop nursery plants, and can be a promising biological alternative to increase the rooting of cuttings. The objective of this study was to assess the viability of producing ‘Powderblue’ blueberry nursery plants from cuttings using different doses of indolebutyric acid (IBA) in association with Azospirillum brasilense. The following treatments were tested: 0 (control); 500 mg L⁻¹ of IBA; 1000 mg L⁻¹ of IBA; A. brasilense; 500 mg L⁻¹ of IBA + A. brasilense; and 1000 mg L⁻¹ of IBA + A. brasilense. The experimental design was completely randomized, with six treatments and four replicates, and each plot (box) consisted of 10 cuttings. The boxes were arranged in a mist chamber with an intermittent regimen controlled by a timer and solenoid valve. After 90 days, the following variables were assessed: rooted cuttings; survival of cuttings; foliar retention; sprouting; cuttings with callus; root dry mass per cutting; number of roots per cutting; and root length. It was observed that the application of IBA with the A. brasilense rhizobacteria increased the number of roots of ‘Powderblue’ blueberry cuttings, while the treatments with IBA alone and IBA 1000 mg L⁻¹ + A. brasilense increased the root length of cuttings. However, treatments with IBA and A. brasilense had no impact on % rooted cuttings and % survival of cuttings. Full article

The yield and quality of horticultural crops mainly depend on genotype, environmental conditions, and cultivation management. Abiotic stresses, such as adverse environmental conditions, can strongly reduce crop performance, with crop yield losses ranging from 50% to 70%. The most common abiotic stresses are represented by cold, heat, drought, flooding, salinity, nutrient deficiency, and high and low light intensities, including ultraviolet radiation. These abiotic stresses affect multiple physiological and biochemical processes in plants. The ability of plants to face these stresses depends on their adaptation aptitude, and tolerant plants may express different strategies to adapt to or avoid the negative effects of abiotic stresses. At the physiological level, photosynthetic activity and light-use efficiency of plants may be modulated to enhance tolerance against the stress. At the biochemical level, several antioxidant systems can be activated, and many enzymes may produce stress-related metabolites to help avoid cellular damage, including such compounds as proline, glycine betaine, amino acids, etc. This special issue gathers eight papers; three are reviews and five are research papers. Two reviews are focused on the application of appropriate agronomic strategies for counteracting the negative effects of abiotic stresses. The third review is based on ornamental plant production under drought stress conditions and the effect on their ornamental quality. The research papers report the effect of climate change on crop development, yield, and quality. Abiotic stresses have been proven to reduce crop performance and yield. Research studies are essential for understanding the key adaptation strategies of plants that can be exploited for improving the crop stress tolerance. Full article

Borage (Borago officinalis L.) is a wild vegetable appreciated as a folk medicine and for culinary preparations. The introduction of borage as a specialized cultivation would allow for the diversification of vegetable crops and would widen the offerings of raw and minimally processed leafy vegetables. Thus, the aim of the research was to evaluate the quality and shelf-life of fresh-cut borage stored at different temperatures. Borage plants were grown during the autumn–winter season and immediately minimally processed after harvest. Fresh-cut borage leaves packed in sealed bags were stored at 2 or 6 °C for 21 d. Weight loss, total soluble solids (TSS), titratable acidity (TA), ascorbic acid, nitrates, leaf color characteristics and overall quality were determined through the storage period. Borage plants were deemed suitable for minimal processing. Storage temperature significantly influenced the rate of quality loss. Borage leaves had an initial nitrate content of 329.3 mg kg⁻¹ FW that was not affected by temperature or storage. TSS and TA were higher in leaves stored at 6 °C. TSS, TA and ascorbic acid content increased during storage. Minimally processed borage leaves stored at 2 °C had lower weight loss and leaf color modifications during storage and a longer shelf life than those stored at 6 °C, so were still marketable after 21 d of storage. Full article