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Chickpea wilt incited by Fusarium oxysporum f. sp. ciceris is one of the most important constraints to chickpea production worldwide and best managed through host plant resistance. The aim of this work was to find new sources of resistance to wilt disease and validate their stability across different environments. One-hundred and twenty three lines with wilt incidence <10% were selected from preliminary evaluation of 948 lines including germplasm and breeding lines from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) for wilt resistance in the sick plot during 2003/2004 crop season at ICRISAT, Patancheru, India. Sixty lines were selected for second round of evaluation (2005/2006) and from those 57 lines were selected for third round of evaluation (2006/2007). In order to validate resistance stability, a Chickpea Wilt Nursery was constituted with 27 lines (7 germplasm accessions, 19 breeding lines and a highly susceptible check) and further tested in multi-location experiment for wilt resistance at 9 locations in India for three years (2007/2008-2009/2010). Variability in wilt incidence due to genetic differences among the genotypes, among the environments, and that due to genotype × environment interaction was highly significant (P < 0.001). Although complete resistance across the locations was not found, the genotype and genotype × environment (GGE) biplot analyses allowed the selection of three breeding lines (ICCV 05527, ICCV 05528 and ICCV 96818) and one germplasm accession (ICC 11322) with moderate level of disease resistance and stable performance across the environments. Genotype × environment (G × E) interaction contributed 36.7% of total variation of the multi-environment evaluation, revealing instability of the phenotypic expression across environments. The identified resistant sources should be useful to chickpea disease resistance breeding programs.

Thirty two pathogenic isolates of Fusarium udum from different pigeonpea growing areas in India were studied for pathogenic and molecular variability. Pathogenic variability was tested on 12 pigeonpea differential genotypes, which revealed prevalence of five variants in F. udum. The amount of genetic variation was evaluated by Polymerase Chain Reaction (PCR) amplification with 20 random amplified polymorphic DNA (RAPD) markers and nine microsatellite markers. All amplifications revealed scorable polymorphisms among the isolates, and a total of 137 polymorphic fragments were scored for the RAPD markers and 16 alleles for the simple sequence repeat (SSR) markers. RAPD primers showed 86% polymorphism. Genetic similarity was calculated using Jaccard's similarity coefficient and cluster analysis was used to generate a dendrogram showing relationships between them. Isolates could be grouped into three subpopulations based on molecular analysis. Results indicated that there is high genetic variability among a subpopulation of F. udum as identified by RAPD and SSR markers and pathogenicity on differential genotypes.

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