The Number of Genes Controlling Resistance in Beans to Common Blight
Ten crosses were made between resistant (R), susceptible (S), RxS susceptible and Intermediate (I), SxI and RxR bean lines to common bacterial blight. The F1 were advanced to F2 and in each cross over 250 F2 plants were used to evaluate for the number of genes controlling resistance using Mendelian genetics and Stanifield’s formula. The plants were inoculated by razor blade method on the leaves and by needle scratch on the pods and evaluated at V3 (3rd trifoliate leaf stage), R6 (flowering stage) and on pods. Using Mendelian genetics mono to polygenic resistance was found to control resistance to common blight in the crosses evaluated at the three growth stages of the bean plant. At V3, two to many genes were found to control resistance with segregation ratios that were significantly (P≤0.05) different from that of three gene pairs. In some crosses transgressive segregation was observed. By application of appropriate variances to the equation provided by Stanisfield’s formula, the number of genes in the ten crosses was one to four at V3 one to three at R6 and one or two for pod resistance.
Keywords: Common blight, genes, phaseolus beans, resistance