INTERACTION OF TEMPERATURE AND LIGHT ON THE SEEDLING REACTION OF McMURACHY WHEAT TO RACE 15B OF STEM RUST

Abstract

The reactions of seedlings of McMurachy wheat to stem rust (Puccinia graminis Pers. f. sp. tritici Erikss. & Henn.) race 15B were determined in growth chambers under various combinations of temperature and light. Experiments in continuous light on seedlings kept at temperatures alternating between 62° F. and 72° F. showed that the critical period determining reaction to rust was the time at which symptoms of infection (i.e. flecking) became visible. Experiments involving temperatures of 60°, 70°, and 75° F. at a photoperiod of 16 hr., with 8 hr. of darkness, showed that a 16-hr. period of low temperature (60° F.) and light induced resistance to the rust if this period fell between 51 and 115 hr. after inoculation but was most effective if it occurred between 75 and 91 hr.