Inheritance of ashy stem blight resistance in Andean common bean cultivars ‘Badillo’ and ‘PC 50’ and genetic relationship between Andean A 195 and ‘PC 50’

Abstract

Ashy stem blight (ASB) caused by Macrophomina phaseolina (Tassi) Goidanich is a severe disease in common bean (Phaseolus vulgaris L.). Partial resistance has been identified in common and tepary (P. acutifolius A. Gray) bean. However, the genetics of ASB resistance in common bean genotypes within the Andean race is unknown. Our objectives were to determine: (1) the inheritance of ASB resistance in Andean ‘Badillo’ and ‘PC 50’, and (2) the genetic relationship between Andean genotypes A 195 and PC 50. Ashy stem blight resistant (R) Badillo and PC 50 (scores ≤ 3) was crossed with susceptible (S) (scores > 6) breeding line PR1144-5 and pinto ‘Othello’, respectively. Also, crosses between resistant A 195 and PC 50 were conducted. The four parents and their F1 and F2 were inoculated with the PRI16 M. phaseolina isolate and evaluated at 50 d after inoculation in the greenhouse. All F1 plants were susceptible in Badillo/PR1144-5 and PC 50/Othello populations, and the F2 segregated into 3S:1R and 15S:1R, respectively. Thus, one recessive gene and two independent complementary recessive genes were involved in ASB resistance in these populations. In contrast, the F2 derived from F1 resistant plants of A 195/PC 50 population segregated into 3R:1S suggesting that the resistance to ASB was controlled by one dominant gene. The F3 results corroborated the segregation ratios observed in the F2 in all populations. These novel resistant genes could be introgressed or pyramided in common bean cultivars and germplasm breeding lines to increase the levels of ASB resistance.