Potential of thaxtomin A for the control of the Asian soybean rust

Abstract

Several strategies are required to achieve satisfactory control of Asian soybean rust (ASR) caused by the fungus Phakopsora pachyrhizi. The use of resistance inducers represents a helpful alternative for management of this disease, since they can present good results when included in an integrated ASR management programme. The aim of this study was to investigate the effect of the partially purified phytotoxin thaxtomin A (PPT) in the induction of resistance to P. pachyrhizi in soybean plants and the direct effect on urediniospore germination. Detached soybean leaves were used to test the induction of resistance. They were treated with PPT 72 h before inoculation with the fungus. The disease severity was evaluated after 12 days. For gene expression analysis, leaf samples were collected 24 h after the application of the inducer. The results showed that PPT had a direct effect on spore germination. A concentration of 100 µg PPT mL−1 inhibited the germination of P. pachyrhizi urediniospores by 64.7%. The phytotoxin was also able to reduce the severity of ASR in detached leaves, possibly through the activation of defence mechanisms related to the jasmonate/ethylene pathways. The application of PPT resulted in upregulation of the expression of the ACC gene, the precursor of ethylene biosynthesis, which is involved in one of the three signalling pathways of defence in plants. Thus, these results suggest that the partially purified thaxtomin A is a potential agent for the control of ASR.