Abstract
Reactions of alfalfa varieties of diverse origin to southern blight (Corticium rolfsii), which is an important disease in warm region of Japan, were tested in the inoculated field of Aichi-ken Agricultural Research Center. Ten varieties and strains were tested twice in space planted conditions in 1972 and in 1973. Seven varieties and strains were common to the first and the second tests. The hypha of southern blight were inoculated repeatedly on the crown of the plants in June and July. Mean percentages of the dead plants by southern blight were 20.6% in the first test and 56.3% in the second test. The dead plants by southern blight were more numerous in 1973 when high temperature continued longer, than in 1972. Cherokee was the highest in the percentage of dead plants by southern blight, followed by du Puits and Europe. The varieties of flemish type seemed more susceptible to the disease than others. The varieties with the lowest dead plant percentage were Moapa and Aikei No.4 throughout the two tests. The varieties adapted to warm region seemed less susceptible to southern blight. The correlation coefficient in percentage of the dead plants between the first and the second test was 0.930, and the varietal difference in analysis of variance for the dead plant percentage was highly significant. It was clearly recognized from these results that alfalfa varieties reacted differently to southern blight, and the difference was mainly caused by genetic variations.
