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Title: Effect of temperature and period of high relative humidity on white mold resistance of selective germplasm from the Pisum core collection

Author
item Porter, Lyndon
item Coffman, Virginia

Submitted to: ARS Sclerotinia Initiative Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 12/1/2007
Publication Date: 1/23/2008
Citation: Porter, L., Coffman, V.A. 2008. Effect of temperature and period of high relative humidity on white mold resistance of selective germplasm from the Pisum core collection. ARS Sclerotinia Initiative Annual Meeting. Bloomington, MN January 23-25. p. 26.

Interpretive Summary:

Technical Abstract: White mold, caused by Sclerotinia sclerotiorum, is a common foliar pathogen of peas that can causes serious disease in both irrigated and dryland peas in the Pacific Northwest and pea production areas in the Midwest of the United States. Fungicides effective in managing white mold in peas are not economical, therefore the development of resistant cultivars is essential. The present research assessed the resistance of eleven pea lines, ten of which had previously been identified as having potential resistance to S. sclerotiorum. The lines were inoculated with an isolate of S. sclerotiorum and incubated at six temperatures (60, 65, 70, 75, 85 ºF) and four incubation periods (12, 24, 48, 72 hours) and maintained in a incubator at 90-100% RH. Resistance to S. sclerotiorum was identified in these lines based on lesion expansion, incubation period, and nodal or internodal stem resistance at different temperatures. Lesion expansion at incubation periods of 24, 48 and 72 hours was greatest at temperatures of 75-85, 70 and 70 ºF for 11, 8 and 10 of the eleven pea lines tested, respectively, indicating that the rate of lesion expansion is greater at higher temperatures (75-85 ºF) during the first 24 hours, and then favored by 70 ºF at incubation periods of 48 to 72 hours. All of the pea lines tested except lines 1204-3, 166084 and the susceptible control, Bolero, were highly resistant (mean nodal resistance score less than 1, 1 = lesion did not expand beyond the initial inoculation point) to S. sclerotiorum at all the temperatures tested when incubated for a 12-hour period. At the 24 hour incubation period only three lines (PI103709, PI164972, and PI169603) were highly resistant and these lines were only highly resistant at 85 ºF. Line PI169603 was the only line that was highly resistant at an incubation period of 24 hours and a temperature of 75 ºF. There were no pea lines that were highly resistant to S. sclerotiorum at any of the temperatures when the incubation periods were greater than 24 hours. The pea lines PI169603 and PI240515 appear to have the best resistance to S. sclerotiorum across all the temperatures and incubation periods based on lesion expansion and nodal resistance values.