title: Expression of systemic resistance in Hordeum vulgare against Erysiphe graminis by treatment with abiotic elicitors
Creators: name: Mitchell, Anne Farquhar
Publisher: name: University of Glasgow
Year: 1998
Subjects: subject: Plant pathology.

description: The effects of 7 chemicals, each at 4 concentrations, were examined to determine their ability to elicit resistance in Hordeum vulgare to Erysiphe graminis. The 3 chemicals and concentrations selected for further investigation were 15mM Sodium Salicylate, 25niM Potassium Phosphate and 20mM Methyljasmonate. Each of these compounds gave significant levels of disease control. A lag period of 48 hours between treatment of the lower leaf with the elicitor and challenge-inoculation of the second leaf was found to give greatest control of powdery mildew. A constant temperature of 22°C and a 16 hour photoperiod were found to be the regimes which gave greatest control of mildew. Each of the 3 chemicals was found to possess antifimgal properties in vitro to the pathogens Pyrenophora avenae and Crinipellis pemiciosa. In vivo only 20mM MJ exhibited antifungal properties against E. graminis. Significant levels of resistance were observed up to 42 days post challenge-inoculation. Significant reductions in infection were still observed when challenge-inoculation of the second leaf was delayed by as much as 28 days. Two alternative methods of eliciting systemic resistance, seed treatment and root drench, were evaluated. They did not provide the level of disease control observed by elicitor treatment of the aerial portion of the plant. Methyljasmonate vapour was evaluated as a potential elicitor of resistance. The vapour from undiluted MJ and the vapour from 20mM MJ were examined. Both were found to give significant reductions in the level of mildew development observed in the second leaf when the lower leaf was vapour treated and tire second leaf was challenge-inoculated with mildew conidia. The optimal lag period between exposure of the first leaf to MJ vapour and challenge-inoculation was found to be 24 hours. The vapour from both undiluted MJ and 20mM MJ displayed antifungal properties in vitro and in vivo against powdery mildew. The MJ precursors Linoleic acid and Linolenic acid were screened at four concentrations for their ability to elicit resistance. Linoleic acid displayed no activity at any of the concentrations screened, but all concentrations of Linolenic acid were effective elicitors of resistance, with 5mM being the most significant. Again, in vitro, both compounds exhibited antifungal properties. The activity of three defence related enzymes, phenylalanine ammonia lyase, peroxidase and lipoxygenase were monitored in the lower 3 leaves of elicitor treated plants and also in elicitor treated plants which had been subsequently challenge-inoculated. This was carried out for the 3 elicitor chemicals selected from the initial screening., 15mM NaSA, 25mM PP and 20mM MJ. In general terms both sets of plants exhibited elevated levels of enzyme activity, in all 3 leaves. Field scale trials of the elicitors 15mM NaSA and 25mM PP showed significant reductions in powdery mildew development and significant increases in plant height, plant dry weight and grain weight. A second field scale trial with 15mM NaSA and 20mM MJ showed superior control with both chemicals relative to commercial standards. 15mM NaSA gave significant increases in plant height, plant dry weight and grain weight. 20mM MJ exhibited a significant decrease in plant height, but significant increases in plant dry weight and grain yield.