Induced resistance on the management of leaf blight in yam

ABSTRACT The aim of this study was to evaluate the effect of both the extract from Allamanda blanchetti (Ab) and the resistance inducer acibenzolar-S-methyl (ASM) on the control of Curvularia eragrostidis and on the induction of resistance mechanisms in seedlings of yam cv. São Tomé (Dioscorea alata). The isolate of C. eragrostidis was obtained from yam leaves with disease symptoms. Mycelial growth and sporulation were evaluated by adding treatments [extract of A. blanchetti 100, 500 and 1000 ppm, ASM (200 mg.L-1), fungicide Mancozeb® (200 g.ha-1), and control consisting of distilled water] to PDA medium. In a greenhouse, 60-day-old seedlings were sprayed with the treatments on both sides of their leaves to the point of runoff, at 0, 24, 48, 96 and 192h intervals, followed by spraying with a spore suspension (1x105 conidia.mL-1). The activity of peroxidases, phenylalanine ammonia lyase (PAL) and β-1,3-glucanase was analyzed in relation to the time of application of treatments. There was no in vitro fungitoxic action of treatments on C. eragrostidis. Extract of Ab and ASM reduced the disease incidence and severity and increased the activity of peroxidases, PAL and β-1,3-glucanase, when applied prior to inoculation with the pathogen. These results indicate the potential of A. blanchetti for C. eragrostidis control in yam plants by the activation of defense mechanisms.