Wednesday, November 7, 2007 - 10:15 AM
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Unraveling the Molecular Bases of Resistance to Pink Snow Mold in Annual Bluegrass (Poa annua L.).

Annick Bertand1, Yves Castonguay1, Tom Hsiang2, Luc Couture1, and Julie Dionne3. (1) Agriculture and Agri-Food Canada, 2560 Hochelaga Blvd, Quebec City, QC G1V 2J3, Canada, (2) Dept. Environmental Biology, University of Guelph, Guelph, ON N1G 2W1, Canada, (3) Royal Canadian Golf Assoc., Royal Canadian Golf Association, Suite 1 - 1333 Dorval Drive, Oakville, ON L6M 4X7, CANADA

Freezing stress and infection of cool season grasses by snow molds (SM) often result in widespread damage to golf greens in the spring. The development of plant material less susceptible to SM and, at the same time, more tolerant to freezing is the most sustainable approach to improve winter survival and quality of golf course grasses. We first screened 30 annual bluegrass genotypes and selected 4 genotypes with low susceptibility and 4 other with high susceptibility to pink snow mold (Microdochium nivale). The evolution of biochemical compounds typically associated with resistance to SM and the acquisition of freezing tolerance was monitored in plants of the two groups after inoculation with the SM fungus, Microdochium nivale. For this purpose, clones of each genotype were cold acclimated under environmentally-controlled conditions. Half of the plants were then inoculated with a mixture of 4 isolates of M. nivale and incubated for up to 43 days at 2°C at >99% R.H. while the remaining plants were left un-inoculated under the same conditions. Plants were sampled before and 11, 17, 30 and 43 days after inoculation. Crown extracts were analysed by HPLC for soluble sugars and amino acids composition. Soluble sugars progressively declined during incubation with more extensive mobilization in inoculated plants. Highly polymerised fructans, previously reported as potential activators of host defence genes, accumulated to higher levels in SM tolerant as compared to SM sensitive genotypes. The concentration of free amino acids increased during incubation and was highest in inoculated plants of SM tolerant genotypes. Two amino acids showed particularly noteworthy patterns: glutamine for which the concentration was related to SM tolerance, and tyrosine, a precursor of secondary defence metabolites, for which the concentration increased rapidly following inoculation and was higher in crowns of SM tolerant genotypes at the end of the experiment.