A gradient of water depths, obtained with the line source irrigation system, and two bean (Phaseolus vulgaris) cultivars, under the conventional and the no-tillage cropping systems, demonstrated increases in white mold intensity caused by Sclerotinia sclerotiorum and sclerotium production with larger water depths. With an initial inoculum concentration of 0.2 sclerotia/kg of soil, the percentage of infected plants varied from 0 to 100% (1998) and from 0 to 12% (1999). A higher and more severe incidence of white mold was verified in plots planted with the cultivar of more prostrate habit, in the conventional cropping system. In both years, disease intensity, production of sclerotia and development of apothecia were lower in the no-tillage cropping system. Finally, in both experiments, about four times more sclerotia was present in the residue of grain collected from conventional tillage plots, than in the no-tillage plots, showing that the production of inoculum for the next crop is much larger in the former than in the latter. This is especially relevant, considering the importance of initial inoculum for monocyclic diseases, such as in the case of white mold, with direct implications for the sustainability of winter bean production in the dry season in Brazil.
Sclerotinia sclerotiorum; sclerotia production; carpogenic germination
