Effects of low-temperature stress on development of winter crown rot in first-year alfalfa

The effects of sub-lethal low temperatures on predisposing first-year alfal fa plants to infection by the low temperature basidiomycete (LTB), find the effects of sub-lethal winter crown rot levels on alfalfa cold hardiness we re evaluated in controlled environment and field studies. Alfalfa, subjecte d to the sublethal stress temperature of -7.5 degrees C for 1 to 5 wk and i noculated with LTB, exhibited higher mortality, lower shoot dry weights, an d higher winter crown rot levels than alfalfa similarly inoculated but non- stressed. Inoculation and incubation of alfalfa with the LTB fungus for 4 w k decreased the freezing resistance of cv. Barrier and cv. Peace alfalfa by 26 and 32%, respectively, compared with the non-inoculated controls. Follo wing inoculation and incubation with LTB, stress temperatures between -6 an d -15 degrees C increased LTB induced mortality in Barrier by 17-54% and in Peace by 10-75%. These results demonstrate that sub-lethal low-temperature stress can act synergistically with winter crown rot pathogen to reduce su rvival and yield in first-year alfalfa.