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Biometric Analyses of the Inheritance of Resistance to Didymella rabiei in Chickpea

First and fifth authors: Department of Field Crops, Vegetables and Genetics, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 76100, Israel; second author: Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel; third author: Department of Soil and Crop Sciences, Crop Biotechnology Center, Texas A&M University, College Station 77843; and fourth author: Department of Field Crops and Natural Resources, Agricultural Research Organization, Gilat Experimental Station, MP Negev 85280, Israel

Historically, the response of chickpea (Cicer arietinum L.) to Didymella rabiei (causal agent of Ascochyta blight) has been mainly related to as complete resistance and it was commonly assayed with qualitative (nonparametric) scales. Two reciprocal populations, derived from intra-specific crosses between a moderately resistant late flowering Israeli cultivar and a highly susceptible early flowering Indian accession, were tested at F₃ and F₄ generations in 1998 and 1999, respectively. A quantitative (parametric) assessment (percent disease severity) was used to evaluate the chickpea field response to Ascochyta blight. The transformed relative area under the disease progress curve (tRAUDPC) was calculated for each experimental unit for further analyses. Heritability estimates of the tRAUDPC were relatively high (0.67 to 0.85) in both generations for both reciprocal populations. The frequency distributions of tRAUDPC of the populations were continuous and significantly departed from normality (Shapiro-Wilk W test; P of W < 0.0001), being all platykurtic and skewed toward either the resistant or the susceptible parental lines. The presence of major genes was examined by testing the relationship between the F₃ and F₄ family means and the within-family variances (Fain's test). Analyses of these relationships suggested that segregation of a single (or few) quantitative trait locus with major effect and possibly other minor loci was the predominant mode of inheritance. The correlation estimates between the resistance and days to flower (r = -0.19 to -0.44) were negative and significantly (P = 0.054 to 0.001) different from zero, which represents a breeding constraint in the development of early flowering cultivars with Ascochyta blight resistance.