Inhibitory effect of sirolimus against white rot of Brassica juncea var. tumida

Abstract

White rot, caused by Sclerotinia sclerotiorum (Lib.) de Bary, has recently become a serious threat to tuber mustard (Brassica juncea var. tumida) cultivation in Hangzhou and other mustard growing parts of Zhejiang province, China. This study was conducted to evaluate the inhibitory effect of sirolimus, a natural macrolide compound, against white rot of mustard tuber caused by S. sclerotiorum in vitro and in vivo. The results showed that sirolimus was able to reduce the mycelial growth, sclerogenesis as well as myceliogenic and carpogenic germinations of three isolates of the pathogen. Application of sirolimus markedly increased activity of β-N-acetyl hexosaminidase, endochitinase and β -1,3-glucanase in plant leaves. Moreover, a significant increase was observed in the level of polyphenoloxidase and peroxidase in plant leaves two and four days after application of sirolimus. The results of in vitro tests showed that sirolimus at the concentration of 100 nM completely inhibited disease severity. The treatment with sirolimus enhanced relative conductivity of S. sclerotiorum mycelia over time compared with control. An increase of carbohydrate leakage was observed in the pathogen mycelia incubated with sirolimus. The content of methane dicarboxylic aldehyde (MDA) markedly increased at 5 h and the highest MDA content was observed after 20 h. Due to exposure to sirolimus, a decrease percentage of catalase activity was observed in pathogen mycelia. In conclusion, this study showed that sirolimus can be considered as an effective substance against white rot of tuber mustard caused by S. sclerotiorum.