INHERITANCE OF THE RESISTANCE TO MACROPHOMINA-PHASEOLINA AND IDENTIFICATION OF RAPD MARKERS LINKED TO THE RESISTANCE GENES IN BEANS

The inheritance of resistance to Macrophomina phaseolina was determine d using traditional approaches and molecular markers. Inheritance stud ies were based on a cross between the resistant accession BAT-477 and the susceptible accession A-70. Resistance to M. phaseolina was examin ed by inoculating bean seeds with soil infested with sclerotia of M. p haseolina. The ratio of resistant to susceptible plants in the F-2 pop ulation was close to 9:7. Bulked segregant analysis identified two ran dom amplified polymorphic DNA (RAPD) markers linked to M. phaseolina r esistance. The first RAPD marker (B459(1600)) was a 1.6-kb band presen t in the susceptible and absent in the resistant plants. The second RA PD marker (B386(900)) was a 0.9-kb band present in the resistant, but absent in the susceptible plants. Each of the RAPD markers segregated in a 3:1 ratio as expected, and the segregation of both markers follow ed a 9:3:3:1 ratio expected for two unlinked loci. In 15 of the 16 F-3 families examined, the genotype of the markers correctly predicted th e genotype (heterozygous or homozygous) for disease resistance. The on e exception could be attributed to recombination between B459(1600) an d the linked susceptible gene. These data were consistent with the hyp othesis that, in BAT-477, resistance to M. phaseolina is controlled by two dominant complementary genes. The symbols Mp-1 and Mp-2 (Macropho mina phaseolina) were proposed for these genes.