Effects of Temperature and Light on Development of Anthracnose on Alfalfa

Abstract

WELTY, R. E., and J. 0. RAWLINGS. 1980. Effects of temperature and light on development of anthracnose on alfalfa. Plant Disease 64:476-478. Anthracnose was more severe in susceptible plants incubated at 24 C than at 16 C. Differences in disease severity were not significant among susceptible plants incubated at light/dark temperatures ranging from 14/10 C to 30/26 C after a 3-day infection period at 16 C or 2 and 3 days at 24 C. The severity of anthracnose was similar in susceptible cultivars Team and Saranac infected at either 16 or 24 C. Anthracnose severity was similar in resistant cultivars Arc, Vangard, and Saranac AR when the temperature during infection was 16 C but was more severe in Saranac AR when the temperature during infection was 24 C. Disease severities of susceptible plants incubated in 1,600, 6,500, and 24,800 lux during the infection period were not statistically different. Anthracnose, caused by Colletotrichum trifolii, limits the growth and persistence of alfalfa (Medicago sativa L.) in various areas of the United States (1,2,10). Generally, Flemish alfalfas are highly susceptible to the disease (16), but procedures for screening alfalfa populations for resistance have been developed (14,18) and resistant cultivars are available (6,11). The effects of survival and dissemination of spores (2,12), age of host seedlings (14), and interaction of three species of Colletotrichum (8) on the development of the disease are known. Despite reports that this disease is severe in warm and humid areas (1,9) and is sometimes called summer decline, the effect of temperature on disease severity is not known. We evaluated disease severity of susceptible and resistant alfalfa cultivars inoculated with C. trifolii incubated at various temperatures. We also examined the effect of various light intensities during and after the infection. The infection period is the time that inoculated seedlings were in the moisture chamber, and the postinfection period is the time between removing the plants from the mist and disease scoring. A portion of these results were reported previously (19).