Comparative in vitro and in planta analyses of extracellular enzymes secreted by the pathogenic fungus Sclerotinia sclerotiorum

Abstract

Dry bean (Phaseolus vulgaris L.) is an important economic crop in Brazil but its yield can be significantly reduced by white mold, a disease caused by Sclerotinia sclerotiorum (Lib.) de Bary, a necrotrophic, highly destructive, and non-host-specific fungus. This fungus secretes numerous cell wall-degrading enzymes such as polygalacturonases, exo-β-1,3-glucanases, xylanases, and cellulases that have been detected during the early stages of infection. In this study, the activities of these enzymes were detected in all carbon sources tested (citrus pectin, cell wall extract from P. vulgaris, carboxymethyl cellulose, and glucose), but the highest levels were found when using citrus pectin and cell wall extract from P. vulgaris. Regardless of the carbon source, pH decreased throughout the culture time. During pathogenesis in dry bean stems, increased enzyme activities were also observed. Reverse transcriptase-polymerase chain reaction experiments showed that the induction of polygalacturonases (sspg1, sspg3, sspg5, sspg6, and sspg7), exo-β-1,3-glucanases, and endo-β-1-4-glucanase in S. sclerotiorum occurred during the early stages of colonization.