Aims: The present study describes the detection and quantification of the Sarocladium oryzae metabolites, helvolic acid and cerulenin in extracts of rice grains collected from plants infected with sheath rot. It also describes the phytotoxicity of these metabolites on rice seedlings.
Methods and results: Helvolic acid and cerulenin in sheath rot-infected rice grains were detected using thin layer chromatography (TLC) and nuclear magnetic resonance (NMR) analyses. On the TLC plates helvolic acid and cerulenin moved as brownish yellow spots and showed R(F) values of 0.61 and 0.49, respectively. A standard assay curve was developed on the basis of selective toxicity of helvolic acid towards Calvibacter michiganensis ATCC 2140 and cerulenin towards Candida albicans 1150. The amounts of helvolic acid and cerulenin on the basis of standard assay curve were 2.2 and 1.75 microg g(-1) of infected seeds. Treatment of IR 36 rice seedlings with metabolites induced chlorosis and reduced shoot length by 20%, root length by 30% and root number by 7% relative to control.
Conclusions: Helvolic acid and cerulenin were detected in infected rice grains and these metabolites induced chlorosis and reduced the seed viability and seedling health of rice.
Significance and impact of the study: Antimicrobial and phytotoxic metabolites, helvolic acid and cerulenin are present in infected grains and reduce the seed viability and seedling health. These metabolites may increase the pathogenic potential and survival of S. oryzae in rice seed by competing with other seed-borne fungi.