p‐aminobenzoic acid and vitamin B9 enhance rice defence against sheath blight disease caused by Rhizoctonia solani

Abstract

AbstractSheath blight is one of the most important rice diseases and its control is generally achieved by the use of fungicides, but the economic and environmental costs involved have led to a search for alternative management approaches. In this study, we evaluated the efficacy of eight defence inducers against the rice sheath blight pathogen, Rhizoctonia solani AG1‐IA. The results showed that 10 mM p‐aminobenzoic acid (PABA) and 3 mM vitamin B9 (VB9)‐treated plants had significantly lower disease indices, at 2.56 and 3.49, respectively, compared to the control at 5.36 in growth room conditions. The direct effect studies showed that PABA significantly suppressed fungal mycelial growth, sclerotial formation and hyphal regeneration ability. However, VB9 showed no effect on mycelial growth but promoted sclerotial formation and hyphal regeneration. Histological observation showed a decreased lesion size and lower amount of hyphal DNA in inducer‐treated leaves. Reverse transcription‐quantitative PCR revealed that OsPR1b was significantly induced by VB9 and the expression of OsPR5 was potentiated by PABA, which indicates that the salicylic acid pathway is possibly involved in VB9‐induced resistance, and the antifungal protein OsPR5 probably contributes partially to PABA protection against R. solani. Immediate control effects of PABA and VB9 were also found after disease establishment. Under greenhouse conditions, the control effects of PABA and VB9 were 29.8% and 40.5%, respectively. These findings reveal that the application of PABA and VB9 to complement plant resistance to sheath blight appears to be an effective strategy.