Relationship between oxalate, oxalate oxidase activity, oxalate sensitivity, and white mold susceptibility in Phaseolus coccineus

Sclerotinia sclerotiorum is a necrotrophic pathogen that devastates the yields of numerous crop species, including beans. The disease in common bean and pea is referred to as white mold. We examined the relationship between oxalate, an established virulence factor of S. sclerotiorum, and partial white mold resistance of scarlet runner bean (Phaseolus coccineus). P. coccineus genotypes PI 255956 ('Mayan White Runner') and PI 535278 (Tars-046A) were more resistant than susceptible 'Wolven Pole'. Sensitivity to oxalate ranked highest for Wolven Pole, lowest for PI 255956, and intermediate for PI 535278. Oxalate concentrations were similar in infected stem tissues of the partially resistant lines and lower than Wolven Pole. Moreover, oxalate oxidase and superoxide dismutase activities were absent in the more resistant lines but induced in Wolven Pole. Collectively, these results suggest that genetic differences in susceptibility to S. sclerotiorum among different P. coccineus lines are partially dependent on oxalic acid.