In this work, we examine the impact of elevated temperature during blueberry fruit ripening on the production and accumulation of anthocyanins, a key antioxidant. We profiled anthocyanins and the expression of their respective biosynthetic genes during ripening in two blueberry cultivars, Biloxi (Southern highbush) and Titan (Rabbiteye), across two seasons at controlled ripening temperatures (20 °C / 30 °C). We characterized 21 anthocyanins with diverse degrees of conjugation that remained largely stable in Titan between the two conditions. In Biloxi, cyanidin- and peonidin-derived anthocyanin signals were consistently reduced at 30 °C compared to 20 °C, corresponding with gene expression. Moreover, we found downregulation of VcF3′H, associated with delphinidin-derived flux, and of VcA3GT and VcBAHD, corresponding to reduced glycosylation and acylation. In Titan, compensatory regulation between VcF3′H and VcF3′5′H, suggesting pathway resilience. Correlation analysis suggested co-regulation within anthocyanin subclasses and inverse relationships between acylated and non-acylated forms. Overall, Titan displayed greater transcriptional and metabolic plasticity under thermal stress, highlighting temperature regulation of anthocyanins in blueberries. Our findings emphasize the need to select thermally resilient genotypes to cope with global warming scenarios.

High ripening temperatures alter blueberry fruit chemistry, yet the underlying metabolite shifts remain poorly defined. In this study, two blueberry cultivars, southern highbush (Vaccinium corymbosum cv. Biloxi) and rabbiteye (Vaccinium virgatum cv. Titan™), were grown under two controlled day/night temperature regimes, 20.0/16.0 °C and 30.0/24.0 °C, for two consecutive seasons. The negative impact of higher temperatures on fruit weight, with reductions of up to 34 %, and the sugar-to-acid ratio was more significant in Biloxi than in Titan, highlighting Titan’s relative advantage in maintaining fruit quality and taste under heat stress. Higher temperatures also impacted total volatile organic compounds in Biloxi, but not in Titan. Still, changes in key volatile organic compounds, including geraniol, linalool, and methyl 2-methylbutanoate, were detected in both cultivars that could impact the berry flavor. Our results demonstrate how temperature affects blueberry physiology and flavor traits and the adaptability of specific cultivars, i.e., Titan, to higher temperatures. The finding stresses the importance of adapting and optimizing genetic traits to environmental factors under climate change.

Application of nitrification inhibitor (NI) is considered as an efficient tool for optimization of N management. The main purpose of this study was to examine the combined effects of N-NH4 level and NI on the performance of blueberry plants grown in low and high pH-buffered substrates. Three levels of N-NH4 (20, 40 or 80 mg L−1) were applied, with or without NI, to southern highbush blueberry plants (Vaccinium corymbosum, cv. Springhigh) grown in sandy substrate with or without CaCO3 (5

The appropriate soil pH for blueberry production is <5.5. However, the exact factors involved in the retardation of blueberry growth at higher pH levels have not yet been completely identified. In this study, we examined the short- and long-term combined effects of pH level and Ca concentrations on root morphology and development in relation to blueberry plant performance. Southern highbush blueberry (Vaccinium corymbosum, cv. Windsor) plants were grown in solutions of pH 4.5 or 7.5 that contained 0, 5, 10, 50 or 100 mg L-1 of Ca. The dimensions of the epidermal cell walls of the roots and the levels of pectin and hemicellulose 1 and 2 in those cells were determined after 1 and 3 days. Concentrations of essential macro and micro-elements in the plant organs, chlorophyll concentrations in the leaves and whole-plant biomass production were measured after 12 weeks. The results demonstrate a rapid (3 days) negative response of root tips at pH 7.5 expressed as reduced dimensions and deformation of the epidermal cell walls. This response was accompanied by reduced concentrations of pectin and hemicellulose 1 in those cell walls. These negative effects of pH 7.5 were amplified by a 100 mg L-1 of Ca over the long term (12 weeks), where the concentrations of P and Ca on the epidermal cell of the root were increased. Additionally, the translocation of Mn from the root to the shoot was retarded. The negative effect of the pH level on roots development and on the Mn translocation were associated with significant reductions in chlorophyll concentrations and biomass production. The results presented in this study demonstrate, for the first time, the negative effect of the combination of slightly alkaline pH and a high Ca concentration on root development, which associated with retarding blueberry plants performance.

Calcareous soils are not suitable for blueberry cultivation. Our aim was to improve the performance of blueberry plants in calcareous soils by using pits filled with growth media in combination with high levels of RNH4+ (proportion of N-NH4+ among the total applied N). Rabbiteye blueberry (Vaccinium virgatum Ait. cv. Ochlockonee) plants were grown in pits filled with a tuff/peat mixture (TP), a sandy soil (S) or a calcareous (CC), in full factorial combination with three levels of RNH4+: 33%, 66% or 100%. The two higher RNH4+ treatments decreased the pH of the low-CaCO3 (S) and no-CaCO3 (TP) media to ≤6.0 over 250 days of fertilization, but did not affect the pH of the CC soil over 650 days. Plant performance was superior in the TP and S media, as compared to the CC soil. The type of growth medium was the dominant factor accounting for the improved plant performance. The plants were sensitive to Mn deficiency in leaves during the spring period. The current results suggest that growing blueberry in pits filled with good aeration and low pH buffering capacity medium in combination with a high level of RNH4+ is a positive approach for its cultivation in calcareous soils.

The increased demand for blueberries and limited availability of low-pH soils have led to the increased use of soilless culture systems. The objective of this study was to evaluate the effect of a wide range of RNH4+ [RNH4+ = 100*N-NH4+/(N-NH4++N-NO3−)] values on the acidification of the growth medium and the nutrient status and performance of blueberry plants. RNH4+ treatments of 25% (AN25, control), 50% (AN50) and 100% (AN100) and a 25% N-NH4+ plus concentrated sulfuric acid (AN25-acid) treatment were applied by fertigation to southern highbush blueberry plants (Vaccinium corymbosum, cv. Sunshine Blue) grown in a soilless substrate (50% tuff, 25% peat, 25% coconut coir). The original solution for the AN25-acid treatment was adjusted to a constant pH of 4.5. The pH and mineral concentrations in the leachate, pH of the growth medium and mineral and chlorophyll concentrations in the leaves were monitored periodically. Plant water uptake was monitored periodically and foliage volumes were calculated at the end of the growing season. Application of high levels of RNH4+ decreased the pH of the leachate and medium to below 5.5 and increased the concentrations of Fe, Mn and Zn in the leachate, as compared to the control treatment. Those treatments also increased the chlorophyll concentrations, total plant water uptake, foliage volumes and leaf Mn concentrations relative to the control treatment. The effects of the high-RNH4+ treatment on acidification and plant performance were not significantly different from the effects of the commonly used AN25-acid treatment. It seems, therefore, that the increased RNH4 reduced the pH of the growth medium to the required level for blueberry production, providing a safer and more environmentally friendly alternative to the use of sulfuric acid.

In natural and agricultural ecosystems, plants are often simultaneously or sequentially exposed to combinations of stressors. Here we tested whether limited water availability (LWA) affects plant response to insect herbivory using two populations of Eruca sativa from desert and Mediterranean habitats that differ in their induced defenses. Considering that such differences evolved as responses to biotic and possibly abiotic stress factors, the two populations offered an opportunity to study ecological aspects in plant response to combined stresses. Analysis of chemical defense mechanisms showed that LWA significantly induced total glucosinolate concentrations in the Mediterranean plants, but their concentrations were reduced in the desert plants. However, LWA, with and without subsequent jasmonate elicitation, significantly induced the expression of proteinase inhibitor in the desert plants. Results of a no-choice feeding experiment showed that LWA significantly increased desert plant resistance to Spodoptera littoralis larvae, whereas it did not affect the relatively strong basal resistance of the Mediterranean plants. LWA and subsequent jasmonate elicitation increased resistance against the generalist insect in Mediterranean plants, possibly due to both increased proteinase inhibitor expression and glucosinolate accumulation. The effect of LWA on the expression of genes involved in phytohormone signaling, abscisic acid (ABA-1) and jasmonic acid (AOC1), and the jasmonate responsive PDF1.2, suggested the involvement of abscisic acid in the regulation of defense mechanisms in the two populations. Our results indicate that specific genotypic responses should be considered when estimating general patterns in plant response to herbivory under water deficiency conditions.

Macrophomina phaseolina is a soilborne fungal pathogen causing crown and root rot in strawberry worldwide. M. phaseolina is one of the most destructive soilborne pathogens of strawberry in the Mediterranean region. M. phaseolina was isolated from different cultivars of strawberry showing crown rot, foliage wilting, charcoal rot and plant mortality, cultivated in Qualubia, El Behera and Ismailia governorates in Egypt, and other regions in Israel. The most effective approach for managing the disease relies on resistant germplasm selected using reliable techniques. Pathogenicity tests using M. phaseolina isolates were conducted for virulence and viability using various methods. Various cultivars of strawberry were inoculated by inserting M. phaseolina microsclerotia-colonized toothpicks into crowns of the plants, compared to plantings into a potted soil mix containing 2.5x10(3) sclerotia mL(-1). All inoculated plants were grown at 30 degrees C under greenhouse conditions. Disease symptoms were observed 4 days after inoculation with plant mortality of all the cultivars occurring approximately 20 days post-inoculation, using the toothpick method. In contrast, the microsclerotia inoculation method appeared to be more accurate in distinguishing susceptibility/tolerance of the tested strawberry cultivars, with initial disease symptoms appearing 2 weeks after inoculation. Using the microsclerotia method, disease symptoms progressed faster in the cultivar 'Festival' that was more susceptible to the pathogen, while the 'Florida 90' cultivar showed an intermediate level of disease, with 'Fortuna' showing the least disease progress over time. Additional cultivars were tested in a screenhouse using the microsclerotia method. A differential mortality rate was observed. Thus, disease screening of resistant germplasm to M. phaseolina should rely on an accurate and reliable inoculation technique.

Macrophomina phaseolina is a soil-borne fungal pathogen infecting many important crop plants. The fungus, which can survive on crop debris for a long period of time, causes charcoal rot disease by secreting a diverse array of cell-wall degrading enzymes and toxins. M. phaseolina thrives during periods of high temperatures and arid conditions, as typically occur in Israel and other countries with a Mediterranean climate. Crop losses due to charcoal rot can be expected to increase and spread to other countries in a warming global climate. Management of this pathogen is challenging, requiring an array of approaches for the various crop hosts. Approaches that have had some success in Israel include grafting of melons and watermelons on resistant squash rootstocks and soil application of fungicide to reduce disease incidence in melons, fumigation and alterations in planting date and mulching of strawberries, and alteration in irrigation regime of cotton. Elsewhere, these approaches, as well as soil amendments and addition of organisms that are antagonistic to M. phaseolina, have had success in some crop situations. Management through host resistance would be the most sustainable approach, but it requires identifying a resistant germplasm for each crop and introgressing the resistance into the leading cultivars. Resistance to charcoal rot is under complex genetic control in most crops, posing a great challenge for its introgression into elite germplasm. Moreover, fast, reliable methods of screening for resistance would have to be developed for each crop. The toothpick-inoculation method used by us holds great promise for selecting resistant germplasm for melons and possibly for sesame, but other methodologies have to be devised for each individual crop.

Macrophomina phaseolina is a typical soilborne fungal pathogen causing crown and root rot in strawberry (Fragaria × ananassa Duch.) worldwide. M. phaseolina has become a major problem for strawberry growers parallel to the phase-out of methyl-bromide since 2004 and is considered the most destructive soilborne pathogen of strawberry since then. Global warming is characterized by extreme weather conditions, in the Mediterranean area, as reflected by long, hot, dry summers without rain and relatively short, cold rainy winters. This together with regulatory restrictions on toxic fumigants creates favorable conditions for M. phaseolina to thrive. Screening for resistant germplasm is currently the most effective and sustainable approach for managing the disease. In order to screen for susceptible/tolerant strawberry cultivars, various inoculation techniques were assessed on five strawberry cultivars. Artificial inoculation of growth medium with naturally infected plant material and the use of the ‘toothpick’ method resulted in no significant differences. However, the use of artificially produced sclerotia in a soil mix at concentrations of 2.5 × 103 sclerotia/g soil exhibited differential cultivar mortality rates. High variation was found among 32 tested strawberry varieties (Israeli and US) grown under outdoor conditions in a screenhouse. Cultivars ‘Pelican’ (US), ‘Orly’, ‘Tamir’ and ‘Rotmy’ were considered tolerant compared to cultivars ‘Florida 90’ (US) and ‘Peles’ that were the most susceptible. The overall results indicate that the choice of certain Israeli and US cultivars may provide future germplasm for resistance breeding against M. phaseolina.

Blueberry production is limited to acidic soils (pH < 5.5) for reasons that are not thoroughly understood. The objective of this study was to examine the effects of proportion of N-NH4+ among the total applied inorganic N {N-NH4+/(N-NH4++N-NO3¯)} (RNH4+) on rabbiteye blueberry plant growth and mineral uptake under different CaCO3 soil levels. Rabbiteye blueberry (Vaccinium virgatum Ait., cv. TitanTM) plants were grown in sandy soil mixed with four levels of applied CaCO3 [0 (control, without any added CaCO3), 1%, 5%, or 10% (w/w)] in full factorial combination with three levels of RNH4+ (33%, 66%, or 100%), which were applied through a fertigation system. Leachate pH, biomass accumulation, the concentration of chlorophyll in the leaves, and the concentrations of minerals in leaves and stems were measured. Increased rates of RNH4+ induced acidification of the leachate solution, which was diminished by the increasing rates of applied CaCO3 in the soil. Biomass production decreased linearly as the leachate pH rose above 5.5. Biomass production was positively associated with increased Mn concentrations in the leaves and with decreased Ca concentrations in the stems. The current study demonstrates that the application of high levels of RNH4+ can reduce the pH of neutral and alkaline soils with moderate level of CaCO3 below the threshold (5.5), and enables the production of rabbiteye blueberry in unsuitable soils.

Furanocoumarins (FCs) are a group of related plant defense metabolites occurring in several plant families, including some species in the genus citrus, such as grapefruit and pummelo. FCs function as toxins against pathogens, insects and other plant pests and some are toxic to humans at high levels. Although the levels of FCs in grapefruits are non-toxic to humans, they inhibit the intestinal enzyme CYP3A, thus preventing degradation of medicines, such as statins, and causing dangerous overdose effects. This overdosing can cause devastating side effects, ranging from stomach bleeding to kidney problems, muscle aches and irregular heartbeats. In the present study, we utilize LC/MS to characterize the levels of FCs pathway intermediates and end products in twelve citrus cultivars, including mandarin (Citrus reticulata), orange [Citrus sinensis (L.) Osbeck], Pummelo [Citrus maxima (Burm.) Merr.], grapefruit (Citrus paradisi Macf.), and two newly selected grapefruit like varieties [(Citrus reticulate) X [Citrus maxima (Burm.) Merr]. The orange and mandarin varieties do not contain FCs or FCs precursor compounds suggesting that this biosynthetic pathway is absent or inactive in mandarins and oranges and therefore a good genetic source for null alleles to FCs biosynthesis. We report the selection and characterization of two new low FCs and seedless grapefruit-like varieties, “Aliza” and “Coocki”, developed by a cross between pummelo and mandarin. Fruits of these varieties resemble grapefruit and contain high levels of the flavanone naringin, typical of grapefruit, but contain only trace amounts of FCs (based on LCMS analysis). Based on the variability of FCs content and inheritance in citrus species, the results suggest that future development of new low-FCs grapefruit varieties is an achievable objective.

The sweet melon fruit is characterized by a metabolic transition during its development that leads to extensive accumulation of the disaccharide sucrose in the mature fruit. While the biochemistry of the sugar metabolism pathway of the cucurbits has been well studied, a comprehensive analysis of the pathway at the transcriptional level allows for a global genomic view of sugar metabolism during fruit sink development. We identified 42 genes encoding the enzymatic reactions of the sugar metabolism pathway in melon. The expression pattern of the 42 genes during fruit development of the sweet melon cv Dulce was determined from a deep sequencing analysis performed by 454 pyrosequencing technology, comprising over 350,000 transcripts from four stages of developing melon fruit flesh, allowing for digital expression of the complete metabolic pathway. The results shed light on the transcriptional control of sugar metabolism in the developing sweet melon fruit, particularly the metabolic transition to sucrose accumulation, and point to a concerted metabolic transition that occurs during fruit development.

BACKGROUNDPortulaca oleracea (purslane) is nutritious but, in addition to the essential alpha-linolenic acid, vitamin C and tocopherols, it contains undesirable oxalic acid. Knowing the effects of nitrate and ammonium on oxalate accumulation, we tested the agronomic potential of three members of the P. oleracea aggregate under various nitrogen fertilization conditions, by measuring biomass production and accumulation of fatty acids, organic acids and tocopherol in the commercial P. sativa (Pos) and two natural members: P. nitida (Pon) and P. papillato-stellulata (Pop).RESULTSWith nitrate as the sole N source, we measured differences between Pon and Pos in concentrations of the essential omega-3 fatty acid alpha-linolenic acid. Pos also gained less dry biomass under these conditions, implying a higher agronomical and nutritional value for Pon. Increasing the fertilizer ammonium concentration and reducing that of nitrate significantly decreased oxalic acid by factors of up to 1.7, 2.6 and 3.4 in Pos, Pop and Pon, respectively, significantly increased concentrations of tocopherol and malic acid, had no effect on fatty acids or ascorbic acid, but reduced biomass.CONCLUSIONIn spite of the recumbent growth habit of Pon, the present findings indicate its agronomic potential. Because early flowering and seed production may be the limiting factors in purslane agriculture, growing Pon in nitrate-poor conditions might be agriculturally favorable.

A genetic map of melon enriched for fruit traits was constructed, using a recombinant inbred (RI) population developed from a cross between representatives of the two subspecies of Cucumis melo L.: PI 414723 (subspecies agrestis) and 'Dulce' (subspecies melo). Phenotyping of 99 RI lines was conducted over three seasons in two locations in Israel and the US. The map includes 668 DNA markers (386 SSRs, 76 SNPs, six INDELs and 200 AFLPs), of which 160 were newly developed from fruit ESTs. These ESTs include candidate genes encoding for enzymes of sugar and carotenoid metabolic pathways that were cloned from melon cDNA or identified through mining of the International Cucurbit Genomics Initiative database (http://www.icugi.org/). The map covers 1,222 cM with an average of 2.672 cM between markers. In addition, a skeleton physical map was initiated and 29 melon BACs harboring fruit ESTs were localized to the 12 linkage groups of the map. Altogether, 44 fruit QTLs were identified: 25 confirming QTLs described using other populations and 19 newly described QTLs. The map includes QTLs for fruit sugar content, particularly sucrose, the major sugar affecting sweetness in melon fruit. Six QTLs interacting in an additive manner account for nearly all the difference in sugar content between the two genotypes. Three QTLs for fruit flesh color and carotenoid content were identified. Interestingly, no clear colocalization of QTLs for either sugar or carotenoid content was observed with over 40 genes encoding for enzymes involved in their metabolism. The RI population described here provides a useful resource for further genomics and metabolomics studies in melon, as well as useful markers for breeding for fruit quality.

Resistance to Powdery mildew (PM) disease causes major economic losses in strawberries. Yet, the genetic basis of PM resistance has not been well studied and, as a result, the introduction of new resistant cultivars has been limited. In this study, we aimed to reveal the genetic basis for PM resistance in the octaploid strawberry. Resistant and susceptible accessions were selected and hybridized to produce seven PM-segregating populations. In an effort to develop genetic markers associated with PM resistance, we screened 30 SSR markers, which co-segregate with PM resistance in different populations. In addition, we tested resistance gene analogs (RGAs) as candidate genes for PM disease resistance. The predicted protein alignments of 20 RGAs showed a wide range of sequence identity (35-99%) and were classified into five groups belonging to the Toll and interleukin-1 receptor (TIR) and non-TIR NBS-LRR classes.

Strawberries are grown in Israel during the winter season, with fruit being harvested from early November to May. Most of the strawberry cultivars grown commercially in Israel originate from the national breeding program of the Volcani Institute. Israeli growers have a very narrow window of opportunity in the international market, exporting their premium berries to the European markets before yields arrive from Egypt, Morocco and Spain. Approximately 20% of Israeli fresh strawberry yields (2,000 tons) are exported before, during and after the New Year holidays and bring very high prices. ARO's cv. 'Herut', which was selected in 1998, is an infra short-day, anthracnose-resistant cultivar. It produces an attractive sweet fruit over an extended period in Mediterranean subtropical climates and similar environments. The 'Herut' cultivar is preferred for its early production of high percentage marketable uniform fruits. 'Herut' has large (similar to 24 g) conical fruits with a medium to deep red color. These fruits are moderately firm and have an excellent aromatic, sweet (TSS = 8.5-9.5) flavor. ARO's cv. 'Tamir', is an infra short-day cultivar developed for the Israeli growers as the earliest harvested cultivar in Israel, producing high quality berries for the English and continental European markets from early November. 'Tamir' has recently been released for commercial cultivation and its agronomical adaptation to different environments and its susceptibility to crop diseases are being tested in extensive field trials. 'Tamir' has large (similar to 25 g), firm, conical fruits that exhibit a bright red color with minor blotching variations. The fruit achenes, which are yellow to light red and slightly protruded, give the fruit its nice appearance and, together with its sweet taste, make it a premium berry. These two new ARO strawberry cultivars will provide Israeli growers with added benefits and should increase their profits.