Oz Barazani

Crop wild relatives—undervalued, underutilized and under threat?

The worlds wealth of plant genetic resources has much value for world food security, but these resources are under considerable threat. Crop improvement, particularly under climate change, depends on the genetic diversity of our plant genetic resources, which are arguably inadequately conserved and poorly used. There is wide recognition that the Convention on Biological Diversitys 2010 targets to reduce the loss of biodiversity have not been met. Biodiversity is at risk from multiple threats, including climate change, and the genetic diversity contained within plant genetic resources, particularly of species that are wild relatives of our crops, faces similar threats but is essential to our ability to respond to the new stresses in the agricultural environment resulting from climate change. It is important to consider the genetic value of these crop wild relatives, how they may be conserved, and what new technologies can be implemented to enhance their use.

Back into the Wild – Apply Untapped Genetic Diversity of Wild Relatives for Crop Improvement

Deleterious effects of climate change and human activities, as well as diverse environmental stresses, present critical challenges to food production and the maintenance of natural diversity. These challenges may be met by the development of novel crop varieties with increased biotic or abiotic resistance that enables them to thrive in marginal lands. However, considering the diverse interactions between crops and environmental factors, it is surprising that evolutionary principles have been underexploited in addressing these food and environmental challenges. Compared with domesticated cultivars, crop wild relatives (CWRs) have been challenged in natural environments for thousands of years and maintain a much higher level of genetic diversity. In this review, we highlight the significance of CWRs for crop improvement by providing examples of CWRs that have been used to increase biotic and abiotic stress resistance/tolerance and overall yield in various crop species. We also discuss the surge of advanced biotechnologies, such as next‐generation sequencing technologies and omics, with particular emphasis on how they have facilitated gene discovery in CWRs. We end the review by discussing the available resources and conservation of CWRs, including the urgent need for CWR prioritization and collection to ensure continuous crop improvement for food sustainability.

A comparative analysis of genetic variation in rootstocks and scions of old olive trees – a window into the history of olive cultivation practices and past genetic variation

BackgroundPast clonal propagation of olive trees is intimately linked to grafting. However, evidence on grafting in ancient trees is scarce, and not much is known about the source of plant material used for rootstocks. Here, the Simple Sequence Repeat (SSR) marker technique was used to study genetic diversity of rootstocks and scions in ancient olive trees from the Levant and its implications for past cultivation of olives. Leaf samples were collected from tree canopies (scions) and shoots growing from the trunk base (suckers). A total of 310 trees were sampled in 32 groves and analyzed with 14 SSR markers.ResultsIn 82.7% of the trees in which both scion and suckers could be genotyped, these were genetically different, and thus suckers were interpreted to represent the rootstock of grafted trees. Genetic diversity values were much higher among suckers than among scions, and 194 and 87 multi-locus genotypes (MLGs) were found in the two sample groups, respectively. Only five private alleles were found among scions, but 125 among suckers. A frequency analysis revealed a bimodal distribution of genetic distance among MLGs, indicating the presence of somatic mutations within clones. When assuming that MLGs differing by one mutation are identical, scion and sucker MLGs were grouped in 20 and 147 multi-locus lineages (MLLs). The majority of scions (90.0%) belonged to a single common MLL, whereas 50.5% of the suckers were single-sample MLLs. However, one MLL was specific to suckers and found in 63 (22.6%) of the samples.ConclusionsOur results provide strong evidence that the majority of olive trees in the study are grafted, that the large majority of scions belong to a single ancient cultivar containing somatic mutations, and that the widespread occurrence of one sucker genotype may imply rootstock selection. For the majority of grafted trees it seems likely that saplings were used as rootstocks; their genetic diversity probably is best explained as the result of a long history of sexual reproduction involving cultivated, feral and wild genotypes.

Effect of nitrogen source in the fertilizing solution on nutritional quality of three members of the Portulaca oleracea aggregate

BACKGROUND Portulaca 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). RESULTS With 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. CONCLUSION In 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.

Environmental effects on molecular and phenotypic variation in populations of Eruca sativa across a steep climatic gradient.

Abstract In Israel Eruca sativa has a geographically narrow distribution across a steep climatic gradient that ranges from mesic Mediterranean to hot desert environments. These conditions offer an opportunity to study the influence of the environment on intraspecific genetic variation. For this, we combined an analysis of neutral genetic markers with a phenotypic evaluation in common-garden experiments, and environmental characterization of populations that included climatic and edaphic parameters, as well as geographic distribution. A Bayesian clustering of individuals from nine representative populations based on amplified fragment length polymorphism (AFLP) divided the populations into a southern and a northern geographic cluster, with one admixed population at the geographic border between them. Linear mixed models, with cluster added as a grouping factor, revealed no clear effects of environment or geography on genetic distances, but this may be due to a strong association of geography and environment with genetic clusters. However, environmental factors accounted for part of the phenotypic variation observed in the common-garden experiments. In addition, candidate loci for selection were identified by association with environmental parameters and by two outlier methods. One locus, identified by all three methods, also showed an association with trichome density and herbivore damage, in net-house and field experiments, respectively. Accordingly, we propose that because trichomes are directly linked to defense against both herbivores and excess radiation, they could potentially be related to adaptive variation in these populations. These results demonstrate the value of combining environmental and phenotypic data with a detailed genetic survey when studying adaptation in plant populations. This article describes the use of several types of data to estimate the influence of the environment on intraspecific genetic variation in populations originating from a steep climatic gradient. In addition to molecular marker data, we made use of phenotypic evaluation from common garden experiments, and a broad GIS based environmental data with edaphic information gathered in the field. This study, among others, lead to the identification of an outlier locus with an association to trichome formation and herbivore defense, and its ecological adaptive value is discussed.

Salt-driven interactions between Pistacia lentiscus and Salsola inermis

Background, aim, and scopeIt can be learned from the Pistacia spp. germplasm collection (http://www.bgu.ac.il/pistacia) that the growth of Salsola inermis is inhibited in the vicinity of the evergreen Pistacia lentiscus, but not in the surroundings of the deciduous Pistacia atlantica and Pistacia chinensis. Irrigation of trees during the summer months increases soil salinity around the trees. It was therefore hypothesized that inhibition of S. inermis around P. lentiscus is related to depletion of salt in the vicinity of the latter species.Materials and methodsA multi-approach experimental scheme was carried out which included soil edaphic characterization and germination tests. To test salt tolerance of P. lentiscus, plants were grown in a hydroponic system for a month in medium containing NaCl, while physiological and growth parameters were measured.ResultsConductivity measurements in summer, during the growth season of S. inermis, indicated that soil salinity beneath deciduous Pistacia trees was significantly higher than that below P. lentiscus. Germination of S. inermis seeds on filter paper moistened with P. lentiscus low-conductivity soil filtrate was twice as high as that of the deciduous trees high-conductivity soil filtrates. Nevertheless, fresh and dry weights of mature S. inermis growing next to P. atlantica and P. chinensis were 2.9 to 4.8 times higher than those of plants growing in the vicinity of P. lentiscus. In a hydroponic system, no significant differences were found in growth parameters and stomatal conductance between P. lentiscus growing in control and salt treatments. It was therefore proposed that salt depletion in the vicinity of P. lentiscus inhibits the growth, but not germination, of S. inermis thus confirming the halophylic characteristics of this plant.DiscussionThe nature of Salsola–Pistacia interactions cannot be explained by allelopathic effects; hence, plausible salt-driven interactions were considered. Our data showed that S. inermis accumulated salt and has halophytic characteristics. Interestingly, germination of S. inermis was inhibited in medium containing salt, but the salt was obligatory for further growth, development, and fast biomass production. These results explained the observation of large biomass accumulation in the more saline soil around the deciduous P. atlantica and P. chinensis and the lack of development in the salt-depleted soil around the salt-tolerant accumulator P. lentiscus.ConclusionsSoil salinity around Pistacia trees critically affects the growth of S. inermis. Inhibition of S. inermis growth, but not germination, around the evergreen P. lentiscus, stems from the latter’s ability to deplete salt from its surroundings. The results indicated that P. lentiscus is able to tolerate and accumulate salt, which we assume contributes to its wide distribution along the Mediterranean coast in Israel.Recommendations and perspectivesWhile the phytoremediation potential of Salsola spp. has been explored to some extent, this of P. lentiscus has not been tested and proven before. The results suggest that the evergreen perennial salt-tolerant P. lentiscus can be recommended for horticulture purposes and soil stabilization in relatively saline environments.

Local old olive landrace varieties in Israel—Valuable plant genetic resources in olive cultivation

It is assumed that the cultivation of olive trees started in the East Mediterranean in the third millennia BCE. Throughout history and until recently, successful olive clones were maintained vegetatively and were grafted either on seedlings or on spheroblasts removed from the base of the trunk. It therefore can be hypothesized that local old olive trees, older than 500 years might represent an ancient gene pool. Modern terminology categorizes local genotypes into four main variety groups. However, in traditional terminology these were further differentiated into 27 cultivars according to their phenotypic traits. This genetic diversity, along with the fact that olive trees have been cultivated in a wide range of environmental conditions, might also suggest that adaption to specific conditions played a major role in the selection of rootstocks and scions. We therefore consider it important to start a conservation program of this valuable genetic resource that can be used in future breeding programs.

Genetic variation of naturally growing olive trees in Israel: from abandoned groves to feral and wild?

BackgroundNaturally growing populations of olive trees are found in the Mediterranean garrigue and maquis in Israel. Here, we used the Simple Sequence Repeat (SSR) genetic marker technique to investigate whether these represent wild var. sylvestris. Leaf samples were collected from a total of 205 trees at six sites of naturally growing olive populations in Israel. The genetic analysis included a multi-locus lineage (MLL) analysis, Rousset’s genetic distances, Fst values, private alleles, other diversity values and a Structure analysis. The analyses also included scions and suckers of old cultivated olive trees, for which the dominance of one clone in scions (MLL1) and a second in suckers (MLL7) had been shown earlier.ResultsThe majority of trees from a Judean Mts. population and from one population from the Galilee showed close genetic similarity to scions of old cultivated trees. Different from that, site-specific and a high number of single occurrence MLLs were found in four olive populations from the Galilee and Carmel which also were genetically more distant from old cultivated trees, had relatively high genetic diversity values and higher numbers of private alleles. Whereas in two of these populations MLL7 (and partly MLL1) were found in low frequency, the two other populations did not contain these MLLs and were very similar in their genetic structure to suckers of old cultivated olive trees that originated from sexual reproduction.ConclusionsThe genetic distinctness from old cultivated olive trees, particularly of one population from Galilee and one from Carmel, suggests that trees at these sites might represent wild var. sylvestris. The similarity in genetic structure of these two populations with the suckers of old cultivated trees implies that wild trees were used as rootstocks. Alternatively, trees at these two sites may be remnants of old cultivated trees in which the scion-derived trunk died and was replaced by suckers. However, considering landscape and topographic environment at the two sites this second interpretation is less likely.

A Mixed Bag: The Plant Growth-Promoting Sebacina vermifera Impairs Defense Mechanisms Against Herbivores

Belowground interactions of plants with beneficial plant growth-promoting microorganisms (PGPM) enhance plant growth and fitness and can alter a plant’s ability to cope with its environment. By increasing plant nutritional uptake, PGPM may indirectly enhance a plant’s ability to withstand harsh conditions. However, very often the mode of action of PGPM involves interference with a plant’s hormonal balance, which may have either positive or negative effects on a plant’s interactions with biotic and abiotic stressors. Here we discuss the possibility that the outcome of associating with the genetically similar Sebacina vermifera and Piriformospora indica fungi involves increases in a plant’s susceptibility to herbivores. Defense mechanisms against herbivores are mainly regulated by jasmonic acid and its fine-tuned cross talk with other phytohormones. Thus, the ability of the Sebacinales fungi to produce IAA and shut down defenses against microorganisms by interfering with ethylene synthesis can result in promoting growth effects but at a cost to defense-related signaling pathways. That growth promotion comes at the expense of resistance to herbivore attack calls into question the mutualistic nature of the interaction with these fungi.

Intraspecific variation in defense against a generalist lepidopteran herbivore in populations of Eruca sativa (Mill.)

Abstract Populations of Eruca sativa (Brassicaceae) from desert and Mediterranean (Med) habitats in Israel differ in their defense against larvae of the generalist Spodoptera littoralis but not the specialist Pieris brassicae. Larvae of the generalist insect feeding on plants of the Med population gained significantly less weight than those feeding on the desert plants, and exogenous application of methyl jasmonate (MJ) on leaves of the Med plants significantly reduced the level of damage created by the generalist larvae. However, MJ treatment significantly induced resistance in plants of the desert population, whereas the generalist larvae caused similar damage to MJ‐induced and noninduced plants. Analyses of glucosinolates and expression of genes in their synthesis pathway indicated that defense in plants of the Med population against the generalist insect is governed by the accumulation of glucosinolates. In plants of the desert population, trypsin proteinase inhibitor activity was highly induced in response to herbivory by S. littoralis. Analysis of genes in the defense‐regulating signaling pathways suggested that in response to herbivory, differences between populations in the induced levels of jasmonic acid, ethylene, and salicylic acid mediate the differential defenses against the insect. In addition, expression analysis of myrosinase‐associated protein NSP2 suggested that in plants of the desert population, glucosinolates breakdown products were primarily directed to nitrile production. We suggest that proteinase inhibitors provide an effective defense in the desert plants, in which glucosinolate production is directed to the less toxic nitriles. The ecological role of nitrile production in preventing infestation by specialists is discussed.