Mc Saxena

Genotyping with RAPD and microsatellite markers resolves pathotype diversity in the ascochyta blight pathogen of chickpea

Abstractu2002The poor definition of variation in the ascochyta blight fungus (Ascochyta rabiei) has historically hindered breeding for resistance to the chickpea (Cicer arietinum L.) blight disease in West Asia and North Africa. We have employed 14 RAPD markers and an oligonucleotide probe complementary to the microsatellite sequence (GATA)4 to construct a genotype-specific DNA fragment profile from periodically sampled Syrian field isolates of this fungus. By using conventional pathogenicity tests and genome analysis with RAPD and microsatellite markers, we demonstrated that the DNA markers distinguish variability within and among the major pathotypes of A. rabiei and resolved each pathotypes into several genotypes. The genetic diversity estimate based on DNA marker analysis within pathotypes was highest for the least-aggressive pathotype (pathotype I), followed by the aggressive (pathotype II) and the most-aggressive pathotype (pathotype III). The pair-wise genetic distance estimated for all the isolates varied from 0.00 to 0.39, indicating a range from a clonal to a diverse relationship. On the basis of genome analysis, and information on the spatial and temporal distribution of the pathogen, a general picture of A. rabiei evolution in Syria is proposed.

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.

DNA fingerprinting of Ascochyta rabiei with synthetic oligodeoxynucleotides

SummaryThe ascomycete fungus Ascochyta rabiei, an important pathogen of the grain legume crop chickpea (Cicer arietinum L.) in the Mediterranean region, has not been adequately characterized in molecular terms. We therefore used DNA fingerprinting, with synthetic oligodeoxynucleotides complementary to simple repetitive sequences, to pathotype different isolates of the fungus. Six single-spored A. rabiei isolates were first categorized using a host differential set of nine chickpea genotypes. Seedlings were inoculated under controlled environmental conditions, and disease severity was recorded 9 days after inoculation. DNA was extracted from in vitro-grown mycelia of the six purified fungal isolates, restricted with EcoRI, HinfI, MboII and TaqI, and fingerprinted with radiolabeled (GATA)4, (GTG)5, (CA)8, and (TCC)5, respectively. High levels of polymorphism were detected with optimal enzyme/probe combinations that allow one to discriminate between the isolates. The potential of DNA fingerprinting with simple repetitive sequences can thus be expanded to the identification of fungal races and pathotypes. The characterization of the geographic distribution and genetic variability of pathotypes will facilitate the selection of suitable host cultivars to be grown in specific regions.

ADAPTATION OF LENTIL TO THE MEDITERRANEAN ENVIRONMENT. I. FACTORS AFFECTING YIELD UNDER DROUGHT CONDITIONS

Lentil frequently suffers from drought stress towards the end of the growing season in rainfed Mediterranean farming systems. This study aimed to quantify the contribution of yield potential under irrigated conditions and of drought escape to the adaptation of lentils to drought, and to identify traits of value in selection for adaptation to a rain-fed Mediterranean environment. Twenty-five diverse lentil lines were sown under both irrigated and rainfed conditions in the 1987/88 and 1988/89 seasons in northern Syria. In 1987/88 the total seasonal rainfall was 403 mm and average rainfed biomass and seed yields were 5.0 and 1.8 t ha 1 , respectively. In contrast, in 1988/89 the total season rainfall was 180 mm and average biomass and seed yields were only 0.67 and 0.12 t ha~, respectively. Early vigour (estimated as a visual score) and percentage ground cover were strongly associated with final biomass, and were of value in predicting economic yield (seed + straw). Early maturity was correlated with seed yield. In the dry season 1988/89, 49% of the variation in seed yield among lines was accounted for by variation in flowering time. Drought escape was clearly the key response to drought. For severely drought-prone areas, selection for early flowering is therefore required. Variation in flowering time and seed yield under irrigated conditions accounted for 62% of seed yield variation under drought stress. Adaptation de la lenteja a la sequia

Iron deficiency in lentil: Yield loss and geographic distribution in a germplasm collection

Iron deficiency symptoms are observed on some genotypes of lentil (Lens culinaris Medikus) grown in calcareous soil. A germplasm collection of 3512 accessions originating from 18 countries was characterized for iron deficiency in a Calcic Rhodoxeralf soil at ICARDA, Tel Hadya, Syria in the 1979/80 season. At 105 days after sowing, 592 accessions, representing 16.9% of the collection, showed chlorosis symptoms characteristic of iron (Fe) deficiency. The Fe deficiency was verified by foliar application of Fe-chelate. Germplasm from different countries showed differences in iron deficiency, with those accessions exhibiting symptoms of iron deficiency mostly originating from relatively warm climates such as India (37.5% accessions showing Fe deficiency) and Ethiopia (30%). Populations from those Mediterranean countries where lentil originated (Syria and Turkey) exhibited Fe-deficiency symptoms only at very low frequencies. Fe-deficiency induced chlorosis was positively correlated with cold susceptibility. Fe chlorosis was transient, the deficiency symptoms largely disappearing during reproductive growth at a time, coinciding with increases in soil temperature and daylength-conditions favorable for plant growth. In Indian germplasm, mild deficiency symptoms did not lead to reduced seed yield, but there was a major yield reduction of 47% in those accessions with the most severe symptoms. Straw yields was reduced commensurately with the severity of symptoms. ei]Section editor: B G Rolfe

Adaptation of spring-sown chickpea to the Mediterranean basin. II. Factors influencing yield under drought

Drought during the late vegetative and reproductive stages of development i the major constraint to the productivity of spring-sown chickpea in the rainfed farming systems of West Asia and North Africa. This paper examines the contribution of crop traits to yield under drought and determines the relative contributions of drought escape, yield potential and a drought response index (DRI) to such yield. n nIn years with mild drought (1986/87 and 1987/88), high biomass, high yield potential and high harvest index were highly correlated with grain yield. During the severe drought of 1988/89, early flowering and low straw yield, high harvest index, yield potential, pod and seed number and seed mass were correlated with rainfed grain yield. n nDifferences among chickpea cultivars in rainfed (drought) yield were partitioned into drought escape, yield potential and DRI. Drought escape accounted for 41% in 1986/87, 37% in 1987/88 and 69% in 1988/89; yield potential accounted for 47%, 37% and 1%, respectively; and DRI accounted for 4%, 17% and 17% of the variations, respectively. The three factors combined explained an average of 90% of the variability in grain yield. The DRI was used to quantify tolerance or susceptibility of a cultivar independently of drought escape (early flowering) and yield potential. Of the traits which were significantly associated with drought yield, high harvest index, large number of pod and high seed mass were associated with drought escape (early flowering), while deep root system, high leaf water potential at dawn and large number of seeds were associated with drought tolerance (DRI).

Adaptation of lentil to the Mediterranean environment. II. Response to moisture supply

Lentil is generally grown as a rainfed crop in areas of West Asia and North Africa where rainfall is highly variable. This study aimed to measure genetic responses to variation in moisture supply in the yield of seed and straw, evapotranspiration and water use efficiency, to guide the lentil breeding programme. The response of 25 diverse lentil lines to a soil water gradient was studied in 1987/88 and 1988/89 at Breda, northern Syria, using a line-source sprinkler system. The coefficient of determination between rainfed and irrigated seed yield in the dry 1988/89 season was r2 = 0.26, and the genotypes that were well adapted to dry conditions were different from those well adapted to wet conditions. However, there were also widely adapted genotypes that yielded well under both wet and dry conditions. The selection of such genotypes might be appropriate for the region receiving 300–400 mm annual rainfall, in contrast with the approach to selection suggested for drier areas (less than 300 mm annual rainfall) in a companion article. Soil moisture extraction from the time of maximum profile recharge to maturity in 1987/88 and cumulative crop evapotranspiration in the 1987/88 rainfed crop did not differ among lentil lines. In the irrigated treatment, however, evapotranspiration in the medium to late maturing lines exceeded that in the early maturing lines towards maturity.

Screening techniques and sources of tolerance to salinity and mineral nutrient imbalances in cool season food legumes

A large global land area is affected by saline, alkali (sodic), and acid soil conditions. Cool season food legumes are important crops in many countries with such adverse soils. Tolerant genotypes have been identified in many crops, including legumes. However, very little has been published on selection of tolerant cool season food legume crops. The inadequate knowledge and understanding of the responses of cool season food legume crops to these abiotic stresses, necessitates action by a collaborative network of interdisciplinary teams to make rapid progress in identifying tolerant germplasm and developing cultivars better adapted to unfavorable soil conditions.

Variation in resistance of some forage legumes species to Orobanche crenata Forsk.

Abstract Parasitic weeds of the family Orobanchaceae threaten many forage legumes in the Mediterranean region. Laboratory and field screening of five lines each of six forage legumes (Vicia narbonensis L., V. sativa L., V. villosa ssp. dasycarpa (Ten.) Cavill., Lathyrus sativus L., L. ochrus (L.)D.C., and L. cicera L.) for resistance to the parasitic weed Orobanche crenata Forsk. revealed high interspecific and intraspecific variation. Lathyrus ochrus lines were free of emerged O. crenata shoots while those of L. sativus and L. cicera were highly susceptible to the parasite. Intraspecific variation in reaction to O. crenata was high within V. narbonensis and V. sativa, with several lines being free of Orobanche parasitism whereas others were highly susceptible. Lines with high resistance to Orobanche can reduce the build-up of a seed bank of the parasite in areas where mainly food legumes are grown and can be of value for developing integrated Orobanche control systems. The laboratory screening, which is faster and cheaper, reliably predicted the field performance and hence retesting in the field can be restricted to those lines found resistant in the laboratory.

Effect of vesicular-arbuscular mycorrhiza on vegetative growth and harvest index of chickpea grown in northern Syria

Abstract Determination of the contribution by vesicular-arbuscular mycorrhizal fungi (VAMF) to crop growth under field conditions requires the comparison of non-mycorrhizal or ‘low mycorrhizal’ to ‘high mycorrhizal’ plants. In the Mediterranean region of northern Syria, chickpea ( Cicer arietinum L. cv. ILC 482) plants were grown on a calcareous soil low in NaHCO 3 0extractable phosphorus (P). The indigenous VAMF population was reduced by the fumigant dazomet. Growth and nutrient uptake of non-inoculated chickpea (‘low mycorrhizal’) plants were compared to growth and nutrient uptake of VAMF-inoculated (‘high mycorrhizal’) and P-fertilized chickpea plants. At flowering in ‘high mycorrhizal’ plants, mycorrhizal root length, total P uptake and shoot biomass were significantly higher than in ‘low mycorrhizal’ plants. At maturity, however, shoot biomass was similar, and harvest index was higher in ‘low mycorrhizal’ plants than in ‘high mycorrhizal’ plants. This negative effect on reproductive growth was related to a more shallow root distribution in the soil profile and a lower root: shoot ratio in the ‘high mycorrhizal’ plants. Although chickpea had a benefit from the mycorrhiza in terms of P uptake and vegetative growth, high infection with VAMF reduced reproductive growth, most probably due to higher water consumption and thus drought stress under the Mediterranean conditions.