Genetic and pathogenic diversity within Ascochyta rabiei (Pass.) Lab. populations in Pakistan causing blight of chickpea (Cicer arietinum L.)

Pathogenic and genetic diversity in Ascochyta rabiei populations in Pakista n were evaluated. Biological pathotyping of 130 A. rabiei isolates (obtaine d from hierarchically collected samples) was conducted on a set of three ch ickpea differentials, i.e. ILC 1929 (susceptible), ILC 482 (tolerant) and I LC 3279 (resistant), under controlled conditions. Disease severity data wer e recorded 12 days after inoculation. Statistical analysis grouped the isol ates into three pathotype classes. Four isolates belonged to pathotype I (l east aggressive), 79 isolates to pathotype II (medium aggressive) and 47 is olates to pathotype-III (highly aggressive). Genetic analysis was performed using RAPDs and oligonucleotide fingerprinti ng, where HinfI-digested DNA was hybridized to the P-32-endlabled oligonucl eotide probes (CAA)(5), (GAA)(5), (GA)(8), (CA)(8) and (GATA)(4). Dendrogra ms produced by cluster analysis discriminated 46 genotypes in the A. rabiei population of Pakistan. Genetic distances and relatedness between isolates were calculated. At a genetic distance of 0.3, genotypes were divided into six distinct genotype groups A, B, C, D, E and F containing 16, 11, 2, 5, 5 and 7 isolates, respectively. Most of the genotypes were area specific or predominated in certain areas but did not belong to a distinct pathotype, while most of the aggressive isolates (pathotype III) occurred in Northern Punjab and in the North Western Frontier Province. (C) 2000 Academic Press.