William Erskine

A genetic linkage map of lentil (Lens sp.) based on RAPD and AFLP markers using recombinant inbred lines

Abstract A genetic linkage map of Lens sp. was constructed with 177 markers (89 RAPD, 79 AFLP, six RFLP and three morphological markers) using 86 recombinant inbred lines (F6:8) obtained from a partially interspecific cross. The map covered 1073 cM of the lentil genome with an average distance of 6.0 cM between adjacent markers. Previously mapped RFLP markers were used as anchor probes. The morphological markers, pod indehiscence, seed-coat pattern and flower-color loci were mapped. Out of the total linked loci, 8.4% showed segregation distortion. More than one-fourth of the distorted loci were clustered in one linkage group. AFLP markers showed more segregation distortion than the RAPD markers. The AFLP and RAPD markers were intermingled and clustering of AFLPs was seldom observed. This is the most extensive genetic linkage map of lentil to-date. The marker density of this map could be used for the identification of markers linked to quantitative trait loci in this population.

Screening techniques and sources of resistance to abiotic stresses in cool-season food legumes

SummaryThe adaptability and productivity of cool-season food legumes (chickpea, faba bean, lentil, pea) are limited by major abiotic stresses including drought, heat, frost, chilling, waterlogging, salinity and mineral toxicities. The severity of these stresses is unpredictable in field experiments, so field trials are increasingly supplemented with controlled-environment testing and physiological screening. For drought testing, irrigation is used in dry fields and rain-out shelters in damp ones. Carbon isotope discrimination (Δ13C) is a well-established screen for drought tolerance in C3 cereal crops which is now being validated for use in grain legumes, but it is relatively expensive per sample and more economical methods include stomatal conductance and canopy temperature. Chickpea lines ICC4958 and FLIP87-59C and faba bean line ILB938 have demonstrated good drought tolerance parameters in different experiments. For frost tolerance, an efficient controlled-environment procedure involves exposing hardened pot-grown plants to sub-zero temperatures. Faba beans Cote d’Or and BPL4628 as well as lentil ILL5865 have demonstrated good freezing tolerance in such tests. Chilling-tolerance tests are more commonly conducted in the field and lentil line ILL1878 as well as derivatives of interspecific crosses between chickpea and its wild relatives have repeatedly shown good results. The timing of chilling is particularly important as temperatures which are not lethal to the plant can greatly disrupt fertilization of flowers. Salinity response can be determined using hydroponic methods with a sand or gravel substrate and rapid, efficient scoring is based on leaf symptoms. Many lines of chickpea, faba bean and lentil have shown good salinity tolerance in a single article but none has become a benchmark. Waterlogging tolerance can be evaluated using paired hydroponic systems, one oxygenated and the other de-oxygenated. The development of lysigenous cavities or aerenchyma in roots, common in warm-season legumes, is reported in pea and lentil but is not well established in chickpea or faba bean. Many stresses are associated with oxidative damage leading to changes in chlorophyll fluorescence, membrane stability and peroxidase levels. An additional factor relevant to the legumes is the response of the symbiotic nitrogen-fixing bacteria to the stress.

CURRENT AND FUTURE STRATEGIES IN BREEDING LENTIL FOR RESISTANCE TO BIOTIC AND ABIOTIC STRESSES

Lentil production is limited by lack of moisture and unfavorable temperatures throughout its distribution. Waterlogging and salinity are only locally important. Progress has been made in breeding for tolerance to drought through selection for an appropriate phenology and increased water use efficiency and in breeding for winter hardiness through selection for cold tolerance.The diseases rust, vascular wilt, and Ascochyta blight, caused by Uromyces viciae-fabae, Fusarium oxysporum f. sp. lentis, and Ascochyta fabae f. sp. lentis, respectively, are the key fungal pathogens of lentil. Cultivars with resistance to rust and Ascochyta blight have been released in several countries and resistant sources to vascular wilt are being exploited. Sources of resistance to several other fungal and viral diseases of regional importance are known. In contrast, although the pea leaf weevil (Sitona spp.) and the parasitic weed broomrape (Orobanche spp.), and to a lesser extent the cyst nematode (Heterodera ciceri), are significant yield reducers of lentil, no sources of resistance to these biotic stresses have been found. Directions for future research in lentil on both biotic and abiotic stresses are discussed.

SPATIAL VARIABILITY MODELS TO IMPROVE DRYLAND FIELD TRIALS

Spatial variability in field trials is a reality. A proportion of this is accounted for as inter-block variability by using block (complete or incomplete) designs. A large amount of spatial variability still remains unaccounted for, however, and this may lead to erroneous conclusions. To capture this inexplicable variation (which is mainly due to intra-block variation), yield data from a series of variety yield trials, using cereals and legumes, were analysed using various spatial models. The most suitable of these, selected on the basis of the Akaike Information Criterion, were used to assess the relative performance of genotypes. Although incomplete-block designs have been found to be effective in variety trials, spatial models have added considerable value to trials with legumes and cereals. The ‘best’ spatial models gave efficiency values of over 330% in winter-sown chickpea ( Cicer arietinum ), 140% in lentil ( Lens esculenta ), and 150% in barley ( Hordeum spp.) trials. Furthermore, the use of these best models resulted in a change in the ranking of genotypes (on the basis of mean yield), which resulted, therefore, in a different set of genotypes being selected for high yield. It is recommended that: (i) incomplete block designs be used in variety trials; (ii) the Akaike Information Criterion be used to select the best spatial model; and (iii) genotypes be selected after the use of this model. The selected model would account most effectively for spatial variability in the field trials, improve selection of the most desirable genotypes and, therefore, improve the efficiency of breeding programmes.

Geographic distribution of variation in quantitative traits in a world lentil collection

SummaryIn a world lentil collection the distribution of variation amongst accessions from 13 major lentil-producing countries was examined on the basis of nine quantitative morphological characters by discriminant analysis and canonical analysis. Stepwise discriminant analysis revealed major differences between accessions from different countries. Three major regional groups were apparent: 1) a levantine group (Egypt, Jordan, Lebanon and Syria, 2) a more northern group composed of Greece, Iran, Turkey, and USSR, and 3) accessions from India and Ethiopia with strikingly similar quantitative morphological characters. Misclassifications of individuals within groups were frequent. Characters useful in discriminating between accessions from different countries were in descending order of importance: time to maturity, lowest pod height and 100-seed weight. The regional grouping indicates the importance of local adaptation through clusters of associated characters with phenological adaptation to the ecological environment as the major evolutionary force in the species.

The lentil: botany, production and uses.

1. Introduction 2. Global Production, Supply and Demand 3. Origin, Phylogeny, Domestication and Spread 4. Plant Morphology, Anatomy and Growth Habit 5. Agro-ecology and Crop Adaptation 6. Genetic Resources 7. Genetics of Economic Traits 8. Genetic Enhancement for Yield and Yield Stability 9. Breeding for Short Season Environments 10. Improvement in Developed Countries 11. Advances in Molecular Research 12. Breeding and Management to Minimize the Effects of Drought and Improve Water Use Efficiency 13. Soil Nutrient Management 14. Cropping Systems and Production Agronomy 15. Biological Nitrogen Fixation and Soil Health Improvement 16. Mechanization 17. Diseases and Their Management 18. Insect Pests and Their Management 19. Virus Diseases and Their Control 20. Weed Management 21. Parasitic Weeds 22. Seed Quality and Alternative Seed Delivery Systems 23. Nutritional and Health-beneficial Quality 24. Post-harvest Processing and Value Addition 25. Food Preparation and Use 26. The Impact of Improvement Research.

Lessons for breeders from land races of lentil

Using the ancient, but under-researched, lentil (Lens culinaris Medikus) as an example, the paper charts the spread of the crop from its origins in the Near East arc to its current distribution and reviews the patterns of variation found in its land races to draw lessons for crop improvement. Geographic differentiation of land races is known for sensitivity to temperature and photoperiod in flowering response, base temperature for germination and for winter survival and Fe-efficiency. Collectively such factors condition the specific adaptation in lentil. Cogniscent of this pattern of adaptation, the ICARDA breeding program has decentralized into a series of separate, but finely targeted, streams integrated with national breeding programs. Within land races of lentil there is considerable heterogeneity. To provide some heterogeneity within individual lines of second-cycle genetic material, the breeding program at ICARDA for the West-Asian lowlands is producing F3or4-derived advanced generation bulk lines.

Variation in shoot and root characteristics and their association with drought tolerance in lentil landraces

Lentil (Lens culinaris Medikus subsp. culinaris), generally grown as a rainfed crop, is often subjected to drought. Drought tolerance is closely related to the distribution of root systems in the soil. We studied seedling shoot and root characters in a set of eight randomly selected lentil genotypes collected from Ethiopia, India, Iran, Syria and ICARDA. Each group of genotypes represents a specific adaptation to the environmental conditions associated with its area of origin. The genotypes were evaluated during two seasons (1997 –1999) under field conditions. Thirty-five-day-old seedlings grown in pots in the open air were assessed for stem length, stem weight, taproot length, lateral root number, total root length and total root weight. Combined analyses over 2 years showed that these characters exhibited significant genotypic variability. Stem length, taproot length and lateral root number were highly correlated, both amongst themselves and with yield. High heritability estimates provided reliability in screening based on these traits. Regression analysis showed that stem length alone accounted for 85% of the variance that occurred in seed yield per plant. Cluster analysis showed that the landraces that originated in Iran and Syria, and the breeding lines developed at ICARDA are distinctly different from the lentil accessions that originated in countries at more southerly latitudes (India and Ethiopia). However, of the total of 40 genotypes, only one line (ILL 6002) was strikingly different from all other test genotypes. This line exhibited significantly superior root and shoot traits and yield, and, therefore, is a valuable germplasm for breeding drought tolerant cultivars.

A bottleneck in lentil: widening its genetic base in South Asia

This paper introduces the concept of a bottleneck in lentil (Lens culinaris Medikus) in South Asia and then reviews its rupture. South Asia is the largest lentil growing region in the world and where indigenous lentils show a marked lack of variability. This results from its introduction from Afghanistan around 2000 B.C. and it limits breeding progress. Three approaches to widening the genetic base in the region have been tried, namely plant introduction, hybridization and mutation breeding. Introductions from West Asia flower as indigenous material matures. The asynchrony in flowering has isolated the local pilosae ecotype reproductively. However, the introduction of ILL 4605, an early, large-seeded line, has resulted in its release as ‘Manserha 89’ for wetter areas of Pakistan and its widespread use as a parent in breeding programs in the region. Hybridization between pilosae and exotic germplasm, primarily at International Center for Agricultural Research in the Dry Areas (ICARDA) followed by selection in the sub-continent has resulted in cultivars with improved disease resistance and yield in Bangladesh and Pakistan. Mutation breeding has given new morphological markers and several promising lines. These examples illustrate not only the widening of the genetic base of the lentil in South Asia, but also the evolution of a breeding program of an international center and national programs targeted toward specific adaptation.

Response of wild lentil to Ascochyta fabae f.sp. lentis from Syria

SummaryAscochyta blight induced by Ascochyta fabae f.sp. lentis is a major foliar disease affecting lentil. Screening 248 accessions of the ICARDA wild lentil germplasm collection for resistance to a Syrian isolate of this fungus was conducted under artificial inoculation in a plastic house. The reaction of resistant accessions was confirmed in a second trial. Twenty-four out of 86 accessions of Lens culinaris ssp. orientalis were resistant, as were 12 of 35 accessions of L. culinaris ssp. odemensis, 3 of 35 accessions of L. nigricans ssp. nigricans, 36 of 89 accessions of L. nigricans ssp. ervoides, and all 3 accessions of Vicia montbretii. Sixty-four per cent of resistant sources were from Syria and southeastern Turkey. Disease reaction was uncorrelated both to the altitude of collection and its annual average rainfall. A significant correlation (r = 0.281) between leaflet width and disease reaction was due more to the frequency of the resistant reaction within the narrow-leaved L. nigricans ssp. ervoides than as a function of small leaf area. Disease reaction was uncorrelated with a range of other morphological traits.