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Effect of temperature on latent period of wheat stem rust (Puccinia graminis subsp. graminis f. sp. tritici) isolates across different wheat cultivars.
J. HERNANDEZ NOPSA (1), W. F. Pfender (1). (1) USDA-ARS, Corvallis, OR, U.S.A.

Experiments were conducted to describe the effect of temperature on duration of latent period (LP<sub>50</sub>, time to reach 50% pustules erumpent) of wheat stem rust (WSR). LP<sub>50</sub> of 744, 271, 251, 136, 183, and 275 h were observed for cv. Stephens at 5, 15, 20, 26, 29, and 33.5°C, respectively. LP<sub>50</sub> for cv. McNair were 787, 206, 124, and 253 h at 5,15, 26, and 33.5°C, respectively. Data from both cultivars fit a similar polynomial model. A factorial experiment using four races of WSR (GCCNC, GCCSC, QFCSC, and GFCDC), and four wheat cultivars (Stephens, McNair, Scout 66, and Kingbird) that differ in level of resistance, was conducted at 15°C and 33.5°C. Averaged across cultivars, LP<sub>50</sub> of the races at 15°C ranged from 206 h (QFCSC) to 280 h (GCCNC). LP<sub>50</sub> at 33.5°C ranged from 183 h (GCCNC) to 261 h (GFCDC). Averaged across races, McNair consistently had the shortest LP<sub>50</sub> at 15°C and 33.5°C (221 and 194 h), whereas Stephens (266 h at 15°C) and Kingbird (262 h at 33.5°C) had the longest. Of the 16 race-by-cultivar combinations, at 15°C Kingbird/QFCSC had the shortest LP<sub>50</sub> (194 h) and Stephens/GCCNC the longest (314 h). At 33.5°C McNair/GCCSC had the shortest LP<sub>50</sub> (167 h) and Stephens/GFCDC the longest (275 h). Kingbird was infected only by GCCSC at 33.5°C, whereas it was infected by all four races at 15°C. Across the 16 combinations, infection type was not related to LP<sub>50</sub> duration. Data obtained will be useful in creating an epidemiological model to predict and mitigate WSR.<p><p>Keywords: Fungus, Cereals-Grains, Wheat

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