Inheritance of White Mold Resistance in an Andean Common Bean A 195 and its Relationship with Andean G 122

Abstract

ABSTRACTWhite mold caused by Sclerotinia sclerotiorum (Lib.) de Bary is a devastating disease of common bean (Phaseolus vulgaris L.) in cool and wet production regions of the Americas and elsewhere. Partial resistance is found in common bean, wild bean, and Phaseolus species of the secondary gene pool such as P. coccineus L. The objectives were to determine (i) the inheritance of white mold resistance in a large‐seeded Andean common bean breeding line A 195 in response to contrasting S. sclerotiorum isolates and (ii) the genetic relationship between A 195 and an Andean germplasm accession G 122. White mold resistant (scores ≤ 4) A 195 was crossed with susceptible (scores > 7) pinto ‘Othello’ and resistant G 122. The F1 and the three parents were inoculated with an aggressive S. sclerotiorum isolate ND710 in 2011. Parents and F2 from resistant F1 plants were inoculated with the less aggressive isolate ARS12D at the fifth internode on the main stem and reinoculated (primary branch) with ND710 and evaluated at 35 d in 2012. Two independent complementary dominant genes controlled resistance in the F2 of A 195/Othello in response to either isolate. There was no segregation in A 195/G 122 F2 in response to ARS12D. But a single dominant gene controlled the difference in resistance between A 195 and G 122 to ND710. The F3 results corroborated the F2 segregation ratios in both populations. This information should help introgress and pyramid higher levels of white mold resistance into common bean cultivars of different market classes.