Genetics of resistance to leaf spot disease caused by and in yardlong bean ( ssp. ) × grain cowpea ( ssp. ) populations.

Yardlong bean ( ssp. ), a type of cowpea, is an important vegetable legume of Asia. Cercospora leaf spot (CLS) caused by and is an important phytopathological problem of the yardlong bean grown in tropical regions. The objectives of this study were to (i) determine mode of inheritance of resistance to CLS caused by and , (ii) estimate the heritability of the resistance, (iii) estimate genetic effects on the resistance using six basic populations generated from the cross between the susceptible yardlong bean 'CSR12906' and the resistant grain cowpea ( spp. ) 'IT90K-59-120'. Segregation for the resistance to both fungi in the F population fitted both 3 : 1 ratio and 13 : 3 ratio of susceptible:resistant, while that in the BC2 ((CSR12906×IT90K-59-120)×IT90K- 59-120) population fitted a 1 : 1 ratio, suggesting one recessive gene or two genes with inhibitory gene action control the resistance. Generation mean analysis showed that a simple additive-dominance model was adequate to explain the genetic control of CLS disease resistance, indicating that a single gene controls the resistance. The average number of major genes (effective factors) controlling the resistance was estimated to be 1.05 and 0.92 for and , respectively. The broad-sense heritability calculated for resistance to both diseases was higher than 0.90. Altogether, these results indicated that the resistance to CLS disease caused by and in grain cowpea IT90K-59-120 is a highly heritable trait governed by a single major recessive gene.