Induction of resistance to <i> <scp>P</scp> hytophthora sojae </i> in soyabean ( <i> <scp>G</scp> lycine max </i> ) by salicylic acid and ethylene

Abstract

This study investigated the protective effects of various phytohormones and plant activators on soyabean resistance to P hytophthora sojae , the cause of root and stem rot. It was found that application of benzothiadiazole ( BTH , an activator of salicylic acid ( SA ) signalling) and 1‐aminocyclopropane‐1‐carboxylic acid ( ACC , a precursor of ethylene ( ET ) biosynthesis) markedly induced resistance to P. sojae . By contrast, gibberellin ( GA ) and abscisic acid ( ABA ) rendered soyabean seedlings more susceptible to P. sojae . Simultaneous application of ABA with BTH or ACC suppressed the protective effects of BTH and ACC , indicating that ABA acts antagonistically on the SA ‐ and ET ‐signalling pathways. Neither BTH nor ACC directly inhibited growth of P. sojae . The protective effect of ACC was diminished by co‐treatment with its analogue α‐aminoisobutyric acid, suggesting that ET biosynthesis is required for ACC ‐induced soyabean resistance. Expression analysis of ET ‐ and SA ‐responsive genes demonstrated the activation of ET ‐ and SA ‐signalling pathways during P. sojae infection. Furthermore, ACC treatments augmented the expression of ET ‐responsive and pathogenesis‐related genes. Taken together, the results indicate that ACC ( ET )‐induced soyabean resistance to P. sojae relies on transcriptional augmentation of defence‐related genes.