Genetic System for the Reaction of Field Beans to Beta, Gamma, and Delta Races of Colletotrichum Iindemuthianum1

Abstract

Five cultivars and one breeding line of field bean ( Phaseolus vulgaris L.) were evaluated for their differential reactions to beta, gamma, and delta races of anthraenose ( Collectotrichum lindemuthianum [Sacc. and Magn.] Scrib.). Parental, F 1 and F 2 plants from 10 crosses involving anthraenose resistant and susceptible parents were inoculated with the 3 races. Inoculated plants were maintained in a mist chamber for 8 to 10 days until plants could be classified into resistant and susceptible groups on the basis of their reactions to the pathogen. The F 2 segregation patterns suggested that independent and complementary gene action at 1 or 2 different loci produced a resistant reaction to all races of the pathogen. In addition, an allelomorphic series of three alleles was assumed to be controlling resistance to the beta race. A breeding scheme, involving alternate generations of back-crossing to the recurrent parent and selfing is an effective method to develop resistant cultivars.