Induction of resistance mechanisms in barley by yeast-derived elicitors

Yeast cell-wall extracts (YE) had high phytoalexin elicitor activity on soybeans and induced resistance against barley powdery mildew in the normally highly susceptible cv. Golden Promise. Following treatment with YE there was rapid stimulation of phenylalanine ammonia-lyase (PAL) activity and faster formation of papillae in response to attempted fungal penetration. The spray adjuvants Agral and LI-700 each had poor phytoalexin elicitor activity and caused a slight enhancement of papilla formation and a low level of mildew control. The addition of the adjuvant to YE did not affect phytoalexin elicitation on soybeans but significantly enhanced the speed and the extent of PAL activity, papilla formation and mildew control. It is proposed that this is due to greater coverage and improved persistence enabling increased uptake of YE into the barley leaves.