Genetic marker discovery, intraspecific linkage map construction and quantitative trait locus analysis of ascochyta blight resistance in chickpea (Cicer arietinum L.)

Ascochyta blight, caused by the fungus Ascochyta rabiei (Pass.) Labr., is a highly destructive disease of chickpea (Cicer arietinum L.) on a global basis, and exhibits considerable natural variation for pathogenicity. Different sources of ascochyta blight resistance are available within the cultivated species, suitable for pyramiding to improve field performance. Robust and closely linked genetic markers are desirable to facilitate this approach. A total of 4,654 simple sequence repeat (SSR) and 1,430 single nucleotide polymorphism (SNP) markers were identified from a chickpea expressed sequence tag (EST) database. Subsets of 143 EST-SSRs and 768 SNPs were further used for validation and subsequent high-density genetic mapping of two intraspecific mapping populations (Lasseter x ICC3996 and S95362 x Howzat). Comparison of the linkage maps to the genome of Medicago truncatula revealed a high degree of conserved macrosynteny. Based on field evaluation of ascochyta blight incidence performed over 2 years, two genomic regions containing resistance determinants were identified in the Lasseter x ICC3996 family. In the S95362 x Howzat population, only one quantitative trait locus (QTL) region was identified for both phenotypic evaluation trials, which on the basis of bridging markers was deduced to coincide with one of the Lasseter x ICC3996 QTLs. Of the two QTL-containing regions identified in this study, one (ab_QTL1) was predicted to be in common with QTLs identified in prior studies, while the other (ab_QTL2) may be novel. Markers in close linkage to ascochyta blight resistance genes that have been identified in this study can be further validated and effectively implemented in chickpea breeding programs.