Genetic analyses and conservation of QTL for ascochyta blight resistance in chickpea (Cicer arietinum L.)

Ascochyta blight (AB) caused by Ascochyta rabiei (teleomorph, Didymella rabiei) Pass. Lab. is an important fungal disease of chickpea worldwide. Only moderate sources of resistance are available within the cultivated species and we hypothesized that the available sources may carry different genes for resistance, which could be pyramided to improve field resistance to AB. Four divergent moderately resistant cultivars CDC Frontier, CDC Luna, CDC Corinne, and Amit were each crossed to a highly susceptible germplasm ICCV 96029. Parents, F₁ and F₂ generations were evaluated under controlled conditions for their reactions to AB. A total of 144 simple sequence repeat (SSR) markers were first mapped to eight linkage groups (LG) for the CDC Frontier x ICCV 96029 population. Then based on the evidence from this population, 76, 61, and 42 SSR markers were systematically chosen and mapped in CDC Luna, CDC Corinne, and Amit populations, respectively. Frequency distributions of the AB rating in the F₂ generation varied among the four populations. Composite interval mapping revealed five QTLs (QTL1-5), one on each of LG 2, 3, 4, 6, and 8, respectively, distributed across different sources, controlling resistance to AB. CDC Frontier contained QTL2, 3, and 4 that simultaneously accounted for 56% of phenotypic variations. CDC Luna contained QTL 1 and 3. CDC Corinne contained QTL 3 and 5, while only QTL 2 was identified in Amit. Altogether these QTL explained 48, 38, and 14% of the estimated phenotypic variations in CDC Luna, CDC Corinne, and Amit populations, respectively. The results suggested that these QTLs could be combined into a single genotype to enhance field resistance to AB.