Effects of Leaf Wetness Duration and Temperature on Infection Efficiency, Latent Period, and Rate of Pustule Appearance of Rust in Alfalfa

ABSTRACT Dew and growth chamber tests were conducted on the alfalfa cultivar Ranger to determine the effect of duration of leaf wetness and temperature on several components of the alfalfa rust (Uromyces striatus) monocycle. Duration of leaf wetness and temperature both had significant effects on pustule development. Infection efficiency (number of alfalfa rust pustules per leaf) increased linearly as duration of leaf wetness was increased from 4 to 24 h after inoculation. There was an inverse linear relationship between temperature and infection efficiency as indicated by the slope (-5.73) of the regression line relating the number of pustules per leaf to increasing temperatures between 17.5 and 28°C. Infection efficiency was approximately 20 times greater at 17.5°C than at 28°C. Inoculated alfalfa plants exposed to constant temperatures of 15, 18, 21, 24, 27, or 30°C after an initial 24-h leaf wetness period (19°C) did not significantly affect infection efficiency (P ≤ 0.05), but did affect the time (fr...