Author
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Pfender, William |
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Seguin, Sheila |
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Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/12/1999 Publication Date: N/A Citation: N/A Interpretive Summary: In Oregon's Willamette Valley, a major production area for cool-season grass seed, the stem rust pathogen survives over winter on its grass hosts, and causes epidemics in spring. Stem rust is the area's major disease on perennial ryegrass and tall fescue. To determine the possible importance of freezing temperature on rust survival, infected plants taken from the field were subjected to controlled freezing across a range of temperatures representative of those that can occur in the region. Compared to the nontreated check, there was no significant reduction in rust survival after exposure to -3 deg C or -6 deg C. Exposure of infected plants to -10 deg C caused a 75-90% reduction in rust survival, and exposure to -13 deg C killed all rust infections in tall fescue, and over 99% in perennial ryegrass. Survival of rust infections appeared to be primarily a function of host tissue survival. Between 1960 and 1997, years with winter temperatures as low as -10 deg C and -13 deg C have occurred in the Willamette Valley with frequencies of approximately 39% and 8%, respectively. We conclude that year-to-year variation in winter temperature could have a significant effect on the survival, and consequently the amount of initial spring inoculum, of the grass stem rust pathogen. Technical Abstract: In Oregon's Willamette Valley, Puccinia graminis subsp. graminicola survives over winter on its grass hosts as uredinial infections and causes epidemics of stem rust, the area's major disease on perennial ryegrass and tall fescue. To determine the possible importance of freezing temp. on rust survival, infected plants were subjected to controlled freezing across a range of temps. representative of those that occur in the region. After treatment, plants were placed in a warm greenhouse and the number of actively sporulating pustules was recorded at 3-day intervals for 21 days. The pathogen responded similarly to freezing treatments whether in perennial ryegrass to tall fescue. Compared to the nontreated check, there was no significant reduction in pustule numbers after exposure to -3 deg C or -6 deg C. Exposure to infected plants to -10 deg C caused a 75-90% reduction in rust survival and exposure to -13 deg C killed all rust infections in tall fescue, and over 99% in perennial ryegrass. The decline in rust survival with temperature was slightly steeper for perennial ryegrass than for tall fescue, but the higher absolute number of infections in perennial ryegrass than in tall fescue resulted in higher numbers of surviving infections on perennial ryegrass. Survival of rust infections appeared to be primarily a function of host tissue survival. Between 1960 and 1997, years with winter temperatures as low as -10 deg C and -13 deg C have occurred in the Willamette Valley with frequencies of approx. 39% and 8%, respectively. We could conclude that year-to-year variation in winter temps could have a significant effect on survival, consequently the amount of initial spring inoculum, of the grass stem rust pathogen. |
