Ascochyta blight of chickpea: present status and future priorities

Abstract

A size-selected genomic library comprising 280,000 colonies and representing approximate to 18% of the chickpea genome, was screened for (GA)(n), (GAA)(n) and (TAA)(n) microsatellite-containing clones, of which 389 were sequenced. The majority (similar to 75%) contained perfect repeats; interrupted, interrupted compound and compound repeats were only present in 6%-9% of cases. (TAA)-microsatellites contained the longest repeats, with unit numbers from 9 to 131. For 218 loci primers could be designed and used for the detection of microsatellite length polymorphisms in six chickpea breeding cultivars, as well as in C. reticulatum and C. echinospermum, wild, intercrossable relatives of chickpea. A total of 174 primer pairs gave interpretable banding patterns, 137 (79%) of which revealed at least two alleles on native polyacrylamide gels. A total of 120 sequence-tagged microsatellite site (STMS) markers were genetically mapped in 90 recombinant lines from an inter-species cross between C. reticulatum and the chickpea cultivar ICC 4958. Markers could be arranged in 11 linkage groups (at a LOD score of 4) covering 613 cM. Clustering as well as random distribution of loci was observed. Segregation of 46 markers (39%) deviated significantly (P greater than or equal to 0.05) from the expected 1:1 ratio, The majority of these loci (73%) were located in three distinct regions of the genome. The present STMS marker map represents the most advanced co-dominant DNA marker map of the chickpea genome.