Effects of exudate depletion on sclerotial development of Sclerotinia sclerotiorum and of oxalic acid on the synthesis of phenolic acids in egg plant (Solanum melongena L.)

Abstract

Exudate depletion from Sclerotinia sclerotiorum sclerotia caused poor development of sclerotia, causing reduced sclerotial size and less compactness of the peripheral cell layers. Exudate also showed antifungal activity against some parasitic as well as saprophytic fungi. Aspergillus flavus, Cercospora blumea, Colletotrichum capsici and Fusartum udum showed maximum sensitivity to exudate in undiluted form where less than 40 % conidial germination was recorded. High performance liquid chromatographic (HPLC) analysis of the ethyl acetate fraction of exudate showed that it consisted of tannic, gallic, ferulic and cinnamic acids along with many other unidentified compounds. The exudate-depleted sclerotia were able to cause infection in egg plants (Solanum melongena) in glasshouse. Foliar application of oxalic acid and sclerotial exudate of S. sclerotiorum induced the synthesis of phenolic acids (gallic and cinnamic acid) in treated egg plant leaves. Maximum induction of gallic acid was seen in leaves treated with 0.1 % oxalic acid after 96 h, whereas maximum induction of cinnamic acid was observed in leaves treated with undiluted exudate after 48 h. The lesser amount of cinnamic acid synthesis in leaves in presence of mycelia of S. sclerotiorum indicates the operation of some other resistant reactions other than the phenyl propanoid pathway.