Shahal Abbo

Modified CTAB Procedure for DNA Isolation from Epiphytic Cacti of the Genera Hylocereus and Selenicereus (Cactaceae)

We present a simple protocol for DNA isolation from climbing cacti, genera Hylocereus and Selenicereus. The abundant polysaccharides present in Hylocereus and Selenicereus species interfere with DNA isolation, and DNA extracts, rich in polysaccharides, are poor templates for amplification using polymerase chain reaction (PCR). We used roots as the source tissue due to the lower viscosity of the extracts relative to that of other tissues. The extraction and isolation procedure we devised consists of the following steps: (1) three washes of ground tissue with the extraction buffer to remove the polysaccharides; (2) extraction with high-salt (4 M NaCl) cetyltrimethylammonium bromide (CTAB) buffer to remove the remaining polysaccharides; (3) removal of RNA by RNase; (4) phenol:chloroform extraction to remove proteins; (5) chloroform extraction to remove remaining phenols. The yields ranged from 10 to 20 μg DNA/g fresh roots. DNA samples prepared by our method were consistently amplifiable in the RAPD reaction and gave reproducible profiles.

Genetics of flowering time in chickpea and its bearing on productivity in semiarid environments

Chickpea (Cicer arietinum L.),a grain legume of Near-East origin has a unique natural history. The crop cycle in most of its traditional growing areas is completely different from the autumn germination, spring flowering, and summer maturation of its wild progenitor Cicer reticulatum Ladiz., in eastern Turkey. Millennia of summer cropping in the Near-East and later dissemination into the lower latitude growing areas of eastern Africa and the Indian subcontinent ,as a postrainy season crop, had profound effects on allelic variation in major adaptive loci of chickpea. In this chapter we discuss the consequences of the traditional cropping practices on the flowering time genes of chickpea. The recently identified genes for flowering time are described with special reference to their effect on chickpea adaptation, seed weight, seed yield, and stability under semiarid Near-East and Indian subcontinental growing environments. It is suggested that the genetic research on flowering time of this species and its wild relatives needs much attention, as only two genes affecting this trait are identified so far. Genes allowing a reduced crop cycle will provide pathways for new cropping systems and increased population density. Reduced crop duration may also help chickpea escape damage by the major biotic and abiotic stresses that mostly affect the crop at flowering and podding stages. It is concluded that the relatively simple inheritance of flowering time opens up new possibilities for breeding high yielding and stable chickpea cultivars for the semiarid and arid regions globally.

Viewpoint: Evolution of cultivated chickpea: four bottlenecks limit diversity and constrain adaptation

Chickpea (Cicer arietinum L.) is characterised by a different adaptation profile from the other crops of West Asian origin such as pea, barley, and wheat. In this paper we suggest that a series of four evolutionary bottlenecks occur in chickpea: (1) the scarcity and limited distribution of the wild progenitor, C. reticulatum Ladiz., (2) the founder effect associated with domestication, (3) the shift, early in the crops history, from winter to spring sowing, and the attendant change from using rainfall as it occurs to a reliance on residual soil moisture, and (4) the replacement of locally evolving landraces by elite cultivars produced by modern plant breeding. While two of the bottlenecks are common to all species, the limited distribution of the wild progenitor and shift of cropping from utilisation of current rainfall to stored soil moisture is unique to chickpea. In this paper we suggest that in order to widen the genetic base of cultivated chickpea it is imperative to reintroduce traits from across the primary gene pool. Moreover, a comparative physiological approach to the study of adaptation among the annual wild relatives of chickpea may reveal adaptive strategies within the genus currently obscured by monomorphic loci. The poor state of the world collection of annual wild Cicer species severely constrains the implementation of both these imperatives. We suggest that an extensive collection of annual wild Cicer species, based on ecogeographic principles to maximise the probability of collecting diverse ecotypes, should provide a better understanding of the biology and adaptation in this ancient crop and lead to improved productivity.

Genomic dissection of drought resistance in durum wheat × wild emmer wheat recombinant inbreed line population.

Drought is the major factor limiting wheat productivity worldwide. The gene pool of wild emmer wheat, Triticum turgidum ssp. dicoccoides, harbours a rich allelic repertoire for morpho-physiological traits conferring drought resistance. The genetic and physiological bases of drought responses were studied here in a tetraploid wheat population of 152 recombinant inbreed lines (RILs), derived from a cross between durum wheat (cv. Langdon) and wild emmer (acc# G18-16), under contrasting water availabilities. Wide genetic variation was found among RILs for all studied traits. A total of 110 quantitative trait loci (QTLs) were mapped for 11 traits, with LOD score range of 3.0-35.4. Several QTLs showed environmental specificity, accounting for productivity and related traits under water-limited (20 QTLs) or well-watered conditions (15 QTLs), and in terms of drought susceptibility index (22 QTLs). Major genomic regions controlling productivity and related traits were identified on chromosomes 2B, 4A, 5A and 7B. QTLs for productivity were associated with QTLs for drought-adaptive traits, suggesting the involvement of several strategies in wheat adaptation to drought stress. Fifteen pairs of QTLs for the same trait were mapped to seemingly homoeologous positions, reflecting synteny between the A and B genomes. The identified QTLs may facilitate the use of wild alleles for improvement of drought resistance in elite wheat cultivars.

Mapping quantitative trait loci in chickpea associated with time to flowering and resistance to Didymella rabiei the causal agent of Ascochyta blight.

Drought is the major constraint to chickpea (Cicer arietinum L.) productivity worldwide. Utilizing early-flowering genotypes and advancing sowing from spring to autumn have been suggested as strategies for drought avoidance. However, Ascochyta blight (causal agent: Didymella rabiei (Kov.) v. Arx.) is a major limitation for chickpea winter cultivation. Most efforts to introgress resistance to the pathogen into Kabuli germplasm resulted in relatively late flowering germplasm. With the aim to explore the feasibility of combining earliness and resistance, RILs derived from a cross between a Kabuli cultivar and a Desi accession were evaluated under field conditions and genotyped with SSR markers. Three quantitative trait loci (QTLs) with significant effects on resistance were identified: two linked loci located on LG4 in epistatic interaction and a third locus on LG8. Two QTLs were detected for time to flowering: one in LG1 and another on LG2. When resistance and time to flowering were analyzed together, the significance of the resistance estimates obtained for the LG8 locus increased and the locus effect on days to flowering, previously undetected, was significantly different from zero. The identification of a locus linked both to resistance and time to flowering may account for the correlation observed between these traits in this and other breeding attempts.

Agricultural Origins: Centers and Noncenters; A Near Eastern Reappraisal

Understanding the evolutionary history of crop plants is fundamental to our understanding of their respective adaptation profiles, which in turn, is a key element in securing future yield and quality improvement. Central topics in this field concern the mono- or polyphyletic origin of crop plants, and our ability to identify the geographic location where certain crop plants have originated. Understanding the geographical pattern of domestication may also assist in reconstructing the cultural processes underlying the Neolithic (agricultural) Revolution. Here we review prevailing views on the geographic pattern of Near Eastern plant domestication, and highlight the distinction between genetic domestication events and independent cultural events. A critical evaluation of the wealth of newly published geobotanical, genetic, and archaeological data provides strong support in favor of a specific core area in southeastern Turkey where most, if not all, founder Near Eastern crops were likely domesticated.

Genetic analysis of wheat domestication and evolution under domestication

Wheat is undoubtedly one of the worlds major food sources since the dawn of Near Eastern agriculture and up to the present day. Morphological, physiological, and genetic modifications involved in domestication and subsequent evolution under domestication were investigated in a tetraploid recombinant inbred line population, derived from a cross between durum wheat and its immediate progenitor wild emmer wheat. Experimental data were used to test previous assumptions regarding a protracted domestication process. The brittle rachis (Br) spike, thought to be a primary characteristic of domestication, was mapped to chromosome 2A as a single gene, suggesting, in light of previously reported Br loci (homoeologous group 3), a complex genetic model involved in spike brittleness. Twenty-seven quantitative trait loci (QTLs) conferring threshability and yield components (kernel size and number of kernels per spike) were mapped. The large number of QTLs detected in this and other studies suggests that following domestication, wheat evolutionary processes involved many genomic changes. The Br gene did not show either genetic (co-localization with QTLs) or phenotypic association with threshability or yield components, suggesting independence of the respective loci. It is argued here that changes in spike threshability and agronomic traits (e.g. yield and its components) are the outcome of plant evolution under domestication, rather than the result of a protracted domestication process. Revealing the genomic basis of wheat domestication and evolution under domestication, and clarifying their inter-relationships, will improve our understanding of wheat biology and contribute to further crop improvement.

The Chickpea, Summer Cropping, and a New Model for Pulse Domestication in the Ancient Near East

The widely accepted models describing the emergence of domesticated grain crops from their wild type ancestors are mostly based upon selection (conscious or unconscious) of major features related either to seed dispersal (nonbrittle ear, indehiscent pod) or free germination (nondormant seeds, soft seed coat). Based on the breeding systems (self‐pollination) and dominance relations between the allelomorphs of seed dispersal mode and seed dormancy, it was postulated that establishment of the domesticated forms and replacement of the wild ancestral populations occurred in the Near East within a relatively short time. Chickpea (Cicer arietinum L.), however, appears as an exception among all other “founder crops” of Old World agriculture because of its ancient conversion into a summer crop. The chickpea is also exceptional because its major domestication trait appears to be vernalization insensitivity rather than pod indehiscence or free germination. Moreover, the genetic basis of vernalization response in wild chickpea (Cicer reticulatum Ladiz.) is polygenic, suggesting that a long domestication process was imperative due to the elusive phenotype of vernalization nonresponsiveness. There is also a gap in chickpea remains in the archaeological record between the Late Prepottery Neolithic and the Early Bronze Age. Contrary to the common view that Levantine summer cropping was introduced relatively late (Early Bronze Age), we argue for an earlier (Neolithic) Levantine origin of summer cropping because chickpea, when grown as a common winter crop, was vulnerable to the devastating pathogen Didymella rabiei, the causal agent of Ascochyta blight. The ancient (Neolithic) conversion of chickpea into a summer crop required seasonal differentiation of agronomic operation from the early phases of the Neolithic revolution. This topic is difficult to deal with, as direct data on seasonality in prehistoric Old World field crop husbandry are practically nonexistent. Consequently, this issue was hardly dealt with in the literature. Information on the seasonality of ancient (Neolithic, Chalcolithic, and Early Bronze Age, calibrated 11,500 to 4,500 years before present) Near Eastern agriculture may improve our understanding of the proficiency of early farmers. This in turn may provide a better insight into Neolithic agrotechniques and scheduling. It is difficult to fully understand chickpea domestication without a Neolithic seasonal differentiation of agronomic practice because the rapid establishment of the successful Near Eastern crop package which included wheats, barley, pea, lentil, vetches, and flax, would have preempted the later domestication of this rare wild legume.

Cytology and mating systems in the climbing cacti Hylocereus and Selenicereus

Chromosome numbers and meiotic behavior are reported for the climbing cacti species Hylocereus undatus, Hylocereus polyrhizus, and Selenicereus megalanthus. The Hylocereus spp. are diploid (2n = 22), while S. megalanthus is a tetraploid (2n = 44). Irregular chromosome disjunction at anaphase I in pollen mother cells of S. megalanthus is probably the major cause of its reduced pollen viability and may contribute to low seed set, low number of viable seeds and, consequently, low fruit mass. A pollination study confirmed self-incompatibility in H. polyrhizus and a weakened incompatibility reaction in H. undatus and S. megalanthus. Major crossability barriers do not exist between the Hylocereus spp. investigated. Reciprocal intergeneric crosses were successful between Hylocereus spp. and S. megalanthus, suggesting that an Hylocereus sp. might be one of the diploid progenitors of the tetraploid S. megalanthus. The implications of the results on cacti nomenclature and systematics are briefly discussed.

Reconsidering Domestication Of Legumes Versus Cereals In The Ancient Near East

In this paper, we discuss, from both biological and cultural perspectives, the ancient human-plant liaison that gave rise to Near Eastern agriculture. We explain the biological aspects of Near Eastern plant domestication by a comparative analysis of legume vs. cereal crop evolution. This comparison is illustrated by the natural distribution, ecological affinity, physiology, population structure, floral biology, growth habit, plant stature, seed dispersal mode, and seed dormancy of both wild and domesticated plants of these crop groups. We discuss the differences between Near Eastern legumes and cereals with regard to each of the above aspects, and we highlight the relevance of these differences with regard to Neolithic decision-making, adoption for farming, and subsequent evolution under domestication. We reached the following conclusions: (1) Near Eastern legumes underwent different evolutionary trajectories under domestication as compared with their companion cereals, despite apparent similarities between selection under domestication of both crop groups. (2) Careful comparison of pea, lentil, and chickpea shows that each of the Near Eastern legume crops has a unique evolutionary history in its own right, and this also holds true for the cereal crops. (3) The evolutionary history of each of the Near Eastern crops, prior to as well as after domestication, is well-reflected in its adaptation profile in present-day cropping systems, which determines each crops relative economic importance in different world regions (e.g., chickpea is a major pulse in the Indian subcontinent, and pea is a more important crop in temperate regions, while barley has the widest adaptation, extending from high-latitude temperate regions to semi-arid Mediterranean systems). (4) Ancient choice-making, as reflected in the founder crops repertoire, involved nutritional considerations that may have outweighed grain yield per area and/or time unit criteria.