Evaluating Genetic Association between Fusarium and Pythium Root Rots Resistances in the Bean Genotype RWR 719

Resistance to Fusarium root rot (Fusarium solani f.s.p phaseoli) has been reported in common bean (Phaseolus vulgaris L.) sources and is usually associated with Pythium root rot resistance. Pythium root rot (Pythium ultimum var ultimum) resistance is controlled by a single dominant gene, marked by a SCAR marker PYAA19800. It remains unclear whether the inheritance to resistance of these two bean root rots is genetically independent. We evaluated the association of Fusarium root rot resistance with the Pythium root rots resistance gene and/or the molecular marker PYAA19800 in genotype RWR 719. Two populations; F2 and F2:3 lines, generated from RWR 719 (resistant) × K132 (susceptible) were respectively screened with Fusarium solani and Pythium ultimum isolates, and root damages were scored based on the CIAT 1 – 9 scale. Additionally, the F2:3 lines were screened with PYAA19800. The F2 segregation ratio deviated from a single gene model for reaction to Fusarium solani. The F2:3 lines fit the model for a single dominant gene that confers resistance to Pythium ultimum. Fusarium solani and Pythium ultimum resistances were inherited independently. There was lack of association between PYAA19800 and Fusarium solani resistance, but the PYAA19800 was strongly associated with Pythium ultimum resistance. This contradicts the assertion of linkage of the two resistances that was deduced based on the joint occurrence of both resistances in the available donor genotypes.