Fusarium wilt (Fusarium udum Butler) is an important biotic constraint to pigeonpea (Cajanus cajan L.) production worldwide. Breeding for fusarium wilt resistance continues to be an integral part of genetic improvement of pigeonpea. Therefore, the study was aimed at identifying and validating resistant genotypes to fusarium wilt and determining the magnitude of genotype × environment (G × E) interactions through multi-environment and multi-year screening. A total of 976 genotypes including germplasm and breeding lines were screened against wilt using wilt sick plot at Patancheru, India. Ninety two genotypes resistant to wilt were tested for a further two years using wilt sick plot at Patancheru. A Pigeonpea Wilt Nursery (PWN) comprising of 29 genotypes was then established. PWN was evaluated at nine locations representing different agro-climatic zones of India for wilt resistance during two crop seasons 2007/08 and 2008/09. Genotypes (G), environment (E), and G × E interactions were examined by biplot which partitioned the main effect into G, E, and G × E interactions with significant levels (p ≤ 0.001) being obtained for wilt incidence. The genotype contributed 36.51% of resistance variation followed by the environment (29.32%). A GGE biplot integrated with a boxplot and multiple comparison tests enabled us to identify seven stable genotypes (ICPL 20109, ICPL 20096, ICPL 20115, ICPL 20116, ICPL 20102, ICPL 20106, and ICPL 20094) based on their performance across diverse environments. These genotypes have broad based resistance and can be exploited in pigeonpea 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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Twelve Fusarium oxysporum f. sp. ciceri isolates were isolated from chickpea infected samples collected across different states of India. Pathogenic variability of twelve isolates was observed on seven chickpea cultivars viz., JG 62, Annigeri-1, Chaffa, CPS-1, K 850, L 550 and DCP 92-3. Among the twelve isolates APFOC-1 showed lowest wilt incidence 71.43 per cent and the isolate MPFOC-9 showed 100 per cent wilt incidence in all cultivars. The variability in morphological characters like size, shape, color of conidia and size, shape, color of chlamydospore were observed in all the isolates. The size of macroconidia varied from 9.23X2.53 ìm (WBFOC-12) to 19.3X5.52 ìm (MHFOC-8) with 2-4 septation. The size of microconidia varied from 4.4X2.93 ìm (MPFOC-9) to 8.26X4.2 ìm (MHFOC-8) with 0-1 septation. Macroconidia were sickle shaped and blunt ends with hyaline color. Microconidia were round to oval with hyaline color. Size of chlamydospore varied from 2.67 (UPFOC-11) to 8.24 (JKFOC-5). Chlamydospores did not show much variation with respect to shape and color. Based on the total number of spores observed per microscopic field, the twelve isolates categorized into four groups viz., poor sporulants, moderate sporulants, good sporulants and very good sporulants.

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