Larry D. Robertson

Diversity for abiotic and biotic stress resistance in the wild annual Cicer species

Data on 228 accessions of eight annual wild Cicer species and 20 cultivated chickpea check lines were evaluated for diversity in response to six of the most serious biotic and abiotic stresses which reduce crop yield and production stability of chickpea, i.e., ascochyta blight, fusarium wilt, leaf miner, bruchid, cyst nematode, and cold. Relative frequencies of score reactions to the above six stresses were recorded from all the annual wild Cicer species and the cultivated taxon. Patterns of distribution and amount of variation of the resistance reactions differed between stresses and species. C. bijugum, C. pinnatifidum and C. echinospermum showed accessions with at least one source of resistance (1 to 4 score reactions) to each stress. Overall, C. bijugum showed the highest frequencies of the highest categories of resistance. Next in performance was C. pinnatifidum followed by C. judaicum, C. reticulatum and C. echinospermum. Furthermore, C. bijugum had the highest number of accessions with multiple resistance to the six stresses; two accessions were resistant to five stresses and 16 to four. According to the Shannon-Weaver diversity indices (H′), five species showed discrete mean diversity indices which varied from 0.649 in C. pinnatifidum to 0.526 in C. judaicum, whereas C. chorassanicum, C. cuneatum and C. yamashitae showed the lowest H′s, which were respectively 0.119, 0.174 and 0.216. Pair-wise correlations among the six biotic and abiotic stresses showed the possibility of combining these resistances. Interestingly, multiple resistant accessions were predominantly of Turkish origin.

Genetic diversity and phylogenetic relationships among the annual Cicer species as revealed by isozyme polymorphism

SummaryThere are few estimates of genetic variability within and among populations of the nine annual Cicer species and for the wild species this information is based on few accessions. The present study was undertaken to examine genetic variation within and between annual Cicer species. One hundred and thirty-nine accessions of nine annual Cicer species were used for electrophoretic analysis at ICARDA. High levels of polymorphism in all eight wild annual Cicer species was found. This is in contrast to earlier research which had shown high polymorphism only in C. reticulatum. Cicer reticulatum had the highest proportion of polymorphic loci. However, for the cultigen, among 14 loci assayed, only two were polymorphic, ADH and PGD2. The nine species formed four phylogenetic groups based on the neighbor-joining method. The first group comprised C. arietinum, C. Reticulatum and C. echinospermum, the second C. bijugum, C. judaicum and C. pinnatifidum, the third C. chorassanicum and C. yamashitae; and the fourth group consisted of one species, C. cuneatum. The phylogenetic tree developed from the neighbor-joining technique illustrated that C. reticulatum is the probable progenitor of C. arietinum and that C. echinospermum split off from a common ancestor at an earlier stage in the evolutionary history of Cicer. Genetic diversity data showed that the greatest diversity was within C. reticulatum and the lowest with the cultigen, C. arientinum. With the exception of C. reticulatum, genetic diversity increased with genetic distance from the cultigen. Little geographic variation in genetic diversity was found.

Present status and future strategy in breeding faba beans (Vicia faba L.) for resistance to biotic and abiotic stresses

Progress is being made, mainly by ICARDA but also elsewhere, in breeding for resistance to Botrytis, AScochyta, Uromyces, and Orobanche; and some lines have resistance to more than one pathogen. The strategy is to extend multiple resistance but also to seek new and durable forms of resistance. Internationally coordinated programs are needed to maintain the momentum of this work.

Morphological variation in wild annual Cicer species in comparison to the cultigen

Wild species have been exploited for the transfer of useful genes in most of the major crops, but little has been done in chickpea improvement. Therefore, 228 accessions of eight annual wild Cicer species plus 20 domesticated kabuli chickpea lines were evaluated for 23 vegetative, flower, fruit and seed descriptors at the International Center for Agricultural Research in the Dry Areas (ICARDA), Syria, during 1993/94 to identify useful variations. Large differences between the cultivated and the annual wild taxa were found, especially for leaf area, growth habit, plant height, first pod height, pod dehiscence and 100-seed weight. These findings suggest that these traits underwent major changes during domestication. Although only a small sample of the cultigen was included in this study, C. arietinum showed greater morphological variability compared with the wild taxa. Among the wild taxa, C. reticulatum, C. echinospermum and C. bijugum had the largest variability and were also morphologically closest to the cultigen. Overall, the annual wild Cicer species were of no advantage for direct genetic improvement of agronomic traits in chickpea. Nevertheless, interesting variability was found for a few descriptors: wide leaflets in C. chorassanicum; many branches in C. bijugum and C. reticulatum; and early flowering in C. judaicum.

Mapping the geographical distribution of genetic variation in the genus Lens for the enhanced conservation of plant genetic diversity

Plant genetic resource conservation strategies, informed by an understanding of the geographical distribution of genetic variation within species, are likely to result in a wider representation of conserved diversity in ex situ gene banks and in situ genetic reserves. The main objective of this study was to map the geographical distribution of genetic variation, as revealed by randomly amplified polymorphic DNA (RAPDs), in four wild relatives of the cultivated lentil, namely Lens culinaris ssp. orientalis, L. odemensis, L. ervoides and L. nigricans. Areas of high diversity and unique diversity were located for each taxon, and regions where further germplasm collection was most likely to yield novel genetic variation were identified. There were centres of diversity for L. culinaris ssp. orientalis in southeast Turkey and northwest Syria, and in south Syria and Jordan. A centre of diversity was found to exist in Sweida province, south Syria, for L. odemensis, and for L. ervoides along the coastal border region between Syria and Turkey stretching down along the Syrian coast. There was a centre of diversity for L. nigricans in west Turkey. Analytical techniques previously used at the species level were found to be useful at the genotypic level to objectively target areas for future collection missions, to increase diversity in ex situ collections and to target areas for in situ conservation.

Useful genetic diversity in germplasm collections of food and forage legumes from West Asia and North Africa

The germplasm collections at ICARDA of faba bean, chickpea, lentil and forage legumes have been exploited by breeding programmes in the West Asia and North Africa region for production of improved cultivars. The first lines distributed were taken directly from the germplasm collections after initial evaluation. This formed the first flush of releases by national programmes, with 56 of 106 cultivars emanating from germplasm.A systematic evaluation of the food legumes for a wide range of morpho-agronomic characters based on the IBPGR/ICARDA descriptors has led to publication and widespread distribution of catalogues which, in turn, have led to an extensive use of the germplasm by national breeding programmes. In the period of 1990–1994, more than 5000 accessions of food legumes and more than 1900 accessions of forage legumes have been distributed per year.The most important use made of the germplasm collections has been their exploitation as a source for resistances and tolerances to biotic and abiotic stresses. These legumes often suffer severe yield loss due to disease and environmental stress; consequently, screening procedures were developed for the major biotic and abiotic stresses and were successfully applied in selecting sources of resistances and tolerances.The germplasm collections have also been used to improve the nutritional quality of these crops, both for human and animal consumption. Most of the food legume collections have been screened for protein content. The Lathyrus spp. collections have yielded lines with low levels of the neurotoxin ODAP (β-N-Oxalyl-L-α,β-Diaminopropionic Acid), which causes Lathyrism in humans and animals. These lines are being used extensively in the breeding programme.In addition to maintaining collections of the cultigens, ICARDA has also assembled large collections of wild relatives and progenitors of lentil and chickpea; and wild and weedy forms of the forage legume species. In the past five years the wild Lens and Cicer collections have been evaluated for resistances to biotic and abiotic stresses. These have been useful in providing sources of new, improved or multiple-stress resistance. They have also been useful in increasing yield potential and adaptation of the cultigens.

Contrasting genetic variation amongst lentil landraces from different geographical origins

Lentil landraces from South Asia exhibit a low diversity and discordance with landraces from other countries according to a combination of qualitative and quantitative agromorphological characters. They exhibit specific phenological adaptation to the South Asian environment which precludes the direct use of alien germplasm in breeding programs in South Asia. An understanding of the genetic relationships and diversity of South Asian lentil landraces, in relation to landraces from other countries, is important in attempting to widen the genetic base of germplasm in the region. The objectives of this study were to investigate the genetic relationships between lentil landraces from 3 South Asian countries (India, Nepal and Pakistan) and those from 13 other countries and to determine their relative genetic diversities, using both isozyme electrophoresis and random amplified polymorphic DNA (RAPD) analysis. Polymorphisms were observed for 7 isozyme loci (16 alleles) and 22 RAPD loci. According to Neis genetic distance, germplasm from Afghanistan clustered with that from the South Asian countries. The germplasm from these countries was striking different to that from the other countries studied. Based on genetic distance estimates from RAPD analysis, the countries with the lowest diversity were Pakistan, Afghanistan and Nepal. These data support evidence at the morphological level of a genetic bottleneck in lentil landraces from South Asia. Genetic relationships between countries outside the South Asian group are discussed. Classification into macrosperma and microsperma types did not reflect overall country relationships.

Agricultural potential of Mediterranean grain and forage legumes: 2) Anti-nutritional factor concentrations in the genus Vicia

As part of an investigation into the agricultural potential of under-exploited Mediterranean Viceae, anti-nutritional factor concentrations were measured in the seed of 7 species. These included: V. sativa(subsp. amphicarpa(L.) Batt., subsp. macrocarpa(Moris) Arcang, subsp. nigra(L.) Ehrh., subsp. sativa), V. ervilia L., V. faba L. (var. faba, var. minor Peterm.), V. narbonensis L. (var. aegyptiaca Kornhuber ex Asch. et Schweinf., var. affinis Kornhuber ex Asch. et Schweinf., var. jordanica H. Schaef., var. narbonensis, var. salmonea(Mout.) H. Schaef.), and relatives, including V. johannis Tamamsch., (var. johannis, var. procumbens H. Schaef.), V. hyaeniscyamus Mout., and V. serratifolia Jacq. Both quantitative and qualitative differences in seed chemistry were observed. Condensed tannins, phenolics and proteinase inhibitors were found in varying concentrations in all taxa. The highest concentrations of phenolic secondary metabolites (0.8–1.4% leucocyanidin equivalents, 9.5–16.4 mg/g phenolics) were found in V. faba, the V. narbonensis relatives and V. sativa subsp. macrocarpa. These taxa also tended to contain low levels of proteinase inhibitors (0.25-0.55 mg trypsin/mg protein), whereas the opposite was the case for V. ervilia(2.1 mg t/mg p). V. narbonensis was intermediate both in terms of tannin and proteinase inhibitor levels. In contrast, the non-protein amino acids tended to be more specific in their distribution. Concentrations of canavanine varied from 0.04-0.11% in the seed of V. ervilia, and may constrain the end-use of the grain, given that pigs are sensitive to concentrations as low as 0.08% in their diet. In V. sativa variation of γ-glutamyl-β-cyanoalanine within and between subspecies (0.41–1.36%) is not sufficient to make the grain palatable to monogastrics, since > 0.075% inclusion in the diet causes mortality in chicks. In V. narbonensis, there was no significant variation between most varieties for γ-glutamyl-S-ethenyl cysteine (GEC), a non-protein amino acid peptide which reduces grain palatability. However, lower concentrations were found in V. n. var. jordanica and its near relatives, V. johannis, V. hyaeniscyamus and V. serratifolia(1.3-1.6%, compared with 1.9+/−0.02% in all remaining V. narbonesis sub-species). Anti-nutritional factor concentrations were used to visualize taxonomic relationships using hierarchical cluster analysis. The V. narbonensis varieties were closely aligned with their near relatives, V. johannis, V. hyaeniscyamus and V. serratifolia. In contrast V. faba was positioned closer to the V. sativa subspecies than either to V. narbonesis or its near relatives. V. ervilia was the most distantly related species. Across all taxa proteinase inhibitors and condensed tannins or total phenols were negatively correlated (r=− 0.72, P < 0.009). This may be a mechanism which minimizes wasteful resource allocation to chemical defense, because the 2 anti-nutritional factors are functionally substitutable, since they both reduce the availability of protein in plant material. Thus taxa investing in high concentrations of proteinase inhibitors do not duplicate chemical defense mechanisms by simultaneously producing large amounts of tannins and phenolics.

Population genetic structure in Lens taxa revealed by isozyme and RAPD analysis

An understanding of the genetic structure of populations is vital for the formation of optimum collection, conservation and utilization strategies for plant genetic resources. This is of particular importance in the case of in-situ conservation, a strategy gaining in popularity. The population genetic structures of five wild lentil taxa, Lens culinaris subsp. orientalis, L. odemensis, L. ervoides, L. nigricans and L. lamottei were investigated using isozyme electrophoresis and random amplified polymorphic DNA (RAPD). Approximately 20 plants from each of 5 populations per taxon were screened for variation at 11 isozyme loci and using three RAPD primers. Levels of variation were generally low, although considerable variation existed in the levels of diversity found within populations of L. culinaris subsp. orientalis and L. lamottei. Comparison of the results obtained in this study with the results obtained in a previous study indicate that this is a trend occurring across all species. It implies that levels of diversity within populations must be measured and considered prior to targeting of specific populations for in-situ conservation. Analysis of molecular variance of both isozyme and RAPD data revealed that between 78% and 99% of the variation was attributable to between-population differences. Isozyme results from L. lamottei populations were, however, contradictory. Possible explanations for this difference are discussed.

Agricultural potential of Mediterranean grain and forage legumes: Key differences between and within Vicia species in terms of phenology, yield, and agronomy give insight into plant adaptation to semi-arid environments

In order to identify key adaptive traits which affect productivity in Mediterranean grain and forage legumes and simultaneously determine the agricultural potential of a wide range of Vicia species, germplasm collected from the wild throughout the eastern Mediterranean was grown under semi-arid conditions in Tel Hadya, Syria (313 mm growing season rainfall). These included species currently in use in Mediterranean agriculture, such as V. sativa L., as well as those more widely used in the past-such as V. ervilia L., but also a broad selection from Section Narbonensis (B. Fedtsch. ex Radzhi) Maxted, including V. narbonensis L, V. johannis Tamamsch., V. hyaeniscyamus Mout., V. serratifolia Jacq., and V. kalakhensis Khattab et al. V. faba, a near relative of the taxa in Section Narbonensis, was included as a domesticated control. Where applicable, a representative range of subspecies was used. Accessions were chosen from a wide range of habitats in terms of latitude (31.02–40.72 decimalo), longitude (27.1–43.17 decimalo), altitude (20–1510 m), rainfall (180–1700 mm/yr) and soil depth (5–50 cm) in order to maximise diversity within species. Agricultural potential was determined by measuring seed, hay and biological yield, as well as agronomic traits such as harvest index, standing crop height, and seed size. The comparative influence of phenology and key agronomic traits such as plant habit and seed size on productivity varied tremendously between species, depending on their reproductive strategies. In V. sativa and V. ervilia, the smaller seed species which rely on long vegetative phases and growing seasons to accumulate sufficient biomass to set seed, and in which there was comparatively little agronomic variation, phenology had a large impact on yield. In early emerging taxa such as V. ervilia and V. s. subsp. sativa, with ‘built-in’ long vegetative phases and growing seasons, seed yield was negatively correlated with flower ing (r = −0.86 to −0.88), whereas the opposite was the case for later emerging taxa such as V. s. subsp. nigra (L.) Ehrh. (r = 0.95). Within V. narbonensis and relatives, the larger seeded Vicia species which rely on more conservative reproductive strategies where high seedling vigour associated with large seeds enables the species to enter reproductive phases relatively early, phenology had a much smaller impact on yield than did variation of key traits such as seed weight, plant habit and pod shattering. Among the undomesticated germplasm harvest indices ranged from 0.09–0.31, hay yields from 0.1–3.4 t/ha, seed yield from 0–2.0 t/ha, and dry matter at maturity from 1.6–6.5 t/ha. Sub-specific taxonomy was crucial in determining agronomic potential. V. narbonensis var. aegyptiaca Kornhuber ex Asch. et Schweinf. showed the most potential, combining an upright habit, large seeds (212 mg) and tendency to retain intact pods after maturity, with the highest yield, harvest index and crop height of all the wild Vicia species. V. sativa subsp. sativa, V. ervilia and V. narbonensis var. narbonensis were less productive, but still showed agricultural potential. The smaller seeded V. narbonensis, var. affinis, var. jordanica H. Schäf. and var. salmonea (Mout.) H. Schäf., and their close relatives V. johannis, V. hyaeniscyamus, V. serratifolia and V. kalakhensis have little to offer Mediterranean agriculture on the basis of poor agronomy.