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GENETIC IMPROVEMENT OF LENTIL FOR FUSARIUM WILT RESISTANCE
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Lentil is one of the major components of low-input agriculture in the sub-tropics including parts of Indian sub-continent. It plays an important role in alleviating protein malnutrition for millions of
vegetarian peoples of these regions. The production and productivity of lentil is severely constrained by Fusarium wilt (FW). FW has been reported to cause 100% yield losses, if it affects the crop in the seedling stage. However, recent advances in the identification of races of the pathogen, screening techniques to identify resistant genotypes, genetic dissection and mapping and tagging of resistance genes through molecular markers have resulted in the release of several FW resistant varieties the world over. This has not only narrowed the gaps between potential and realized yields, but also minimized yearly fluctuations in production and productivity of lentil.
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Thirty-two isolates of Fusarium oxysporum f. sp. lentis (Fol) were obtained from wilted lentil plants collected from different lentil growing areas in north-western Algeria. A pathogenicity test was performed for all isolates. Results indicated that the Fol isolates represent a single race but differ in their aggressiveness on the susceptible lines. The amount of genetic variation was evaluated by polymerase chain (PCR) amplification with a set of 6 RAPD primers and 3 AFLP selective nucleotide primer pairs. All amplifications revealed scorable polymorphisms among the isolates, and a total of 8 polymorphic fragments were scored for the RAPD primers and 93 for the AFLP primers. Genetic similarity between each of the isolates was calculated by using the Jaccard similarity coefficient and cluster analysis was used to generate dendogram showing relationship between them. The isolates could be grouped into two subpopulations based on RAPD and AFLP analysis. Results obtained indicate that there is little genetic variability among subpopulation of Fol as identified by RAPD and AFLP markers and that there is no apparent correlation with geographical origin or aggressiveness of isolates. Also, the data suggest that Fol isolates are derived from two genetically distinct clonal lineages.
About 60,000 ha are sown annually to chickpea (Cicer arietinum L.) in Andalucia, southern Spain, approximately 66% of the total national acreage of the crop. Wilt induced by Fusarium oxysporum Schlecht. emend. Snyd. & Hans. f. sp. ciceri (Padwick) Snyd. & Hans. (Foc) severely affects chickpeas in that region causing an average 10% yield loss (Trapero-Casas and Jiménez-Díaz 1985). Control of the disease is mainly by the use of resistant cultivars (Haware and Nene 1980a; Nene and Haware 1980; Nene and Reddy 1987), the efficacy of which is curtailed by the occurrence of pathogen races. Haware and Nene (1982) were the first to show the existence of races of Foc, namely races 1,2,3 and 4, based on the differential interaction among 10 chickpea cultivars and isolates of the pathogen from India. Recent work indicates that resistance to race 1 is conferred by recessive alleles from at least two independent loci (Upadhyaya et al 1983a, 1983b; Singh et al 1987). Cultivars WR 315, CPS 1, BG 212 and JG 74, carrying recessive alleles at both loci, are completely resistant, while cultivars C 104 and K 805, which are homozygous recessive at one of the loci, show a delayed wilt (late-wilting, Haware and Nene 1980b). Cultivar JG 62, which is susceptible to all four races of Foc in India, carries neither of the recessive alleles and shows wilt symptoms within 20 days after sowing (early-wilting).
A total of 47 randomly-selected lentil fields, in the main lentil production regions of South-East Anatolia (SEA), Turkey, were surveyed during May, 1996, for incidence and severity of diseases (fungal and viral), parasitic weeds and insect pests. The lentil growth stage varied from late flowering/early podding to physiological maturity. A total of six fungal and five viral diseases, two parasitic weeds and eight harmful insects were recorded. Amongst fungal diseases, wilt (Fusarium oxysporum Schlecht. emend. Snyder et Hansen f. sp. lentis Vasud. et Srin.), phoma blight (Phoma medicaginis Malbr. et Roum.) and stem rot (Sclerotinia sclerotiorum (Lib.) de Bary) were predominant. The virus diseases detected, based on laboratory tests in samples with yellowing symptoms suggestive of virus infection, were luteoviruses (41% of the samples tested) and faba bean necrotic yellows virus (FBNYV) (15%). Additionally, three seed-borne viruses, namely broad bean stain comovirus (BBSV), pea seedborne mosaic potyvirus (PSbMV) and bean yellow mosaic potyvirus (BYMV), were detected with the former being most prevalent. Orobanche (Orobanche aegyptiaca L.) was prevalent in some production regions. Among insect pests, root aphid (Smythurodes betae West.), ground pearl (Porphyrophora polonica L.) and thrips were the most damaging. These are the first records of Sclerotinia sclerotiorum, Botrytis cinerea, luteoviruses, FBNYV, BBSV, BYMV and PSbMV on lentil in Turkey.
Twenty four isolates of Fusarium oxysporum f. sp. lentis (Fol) collected from different lentil growing areas of the Gangetic plain showed variation with respect to cultural and morphological characters. The extent of genetic diversity was evaluated using a set of 40 RAPD primers and 12 SSR primer pairs, out of which 25 RAPD primers and 9 SSR. primer pairs revealed polymorphisms among the isolates. A total of 217 polymorphic fragments for the RAPD primers and 22 for the SSR primers were scored. Genetic similarity between each the isolates was calculated using the Jaccard similarity coefficient and cluster analysis was used to generate a dendrogram showing relationship between them. The isolates could be grouped into two subpopulations based on RAPD and SSR analysis. Results obtained indicate that there is little genetic variability among a subpopulalion of Fol as identified by RAPD and SSR markers. Also, results indicated that the Fol isolates differ in their aggressiveness on the susceptible lines and that there is no apparent correlation between geographical origin and aggressiveness of isolates.