COMPARISON OF CULTURE CONDITIONS FOR THREE ALTERNARIA SPECIES CAUSING BLACK SPOT OF CABBAGE

Three species of Alternaria, A. brassicicola,A. brassicae and A. japonica, can cause black spot of cabbage. Based on domestics and foreign strains belonging to these three species, a comparative study was conducted to evaluate the effect of temperature, pH, light duration and medium on mycelial growth rate and colony characteristics. The results indicated that the optimum growth temperatures of the three species ranged from 20C to 25C, and those of A. brassicicola and A. japonica increased 5癈 as compared with previous reports. The pH range of mycelial growth was from 4 to 8 for domestic strains of A. japonica while from 3 to 11 for all others. Light duration had little effect on the growth rate of A. brassicicola. However, the growth rate of A. brassicae was significantly higher under 24h light or 12h alternate light than that under 24h darkness. For A. japonica, incubation under 24h light or 24h darkness was more efficient than that under 12h alternate light. PDA was the optimum medium whereas SNA could be a selective medium for Alternaria. The three species could be differentiated on different media based on colony diameter and color. This study indicates the Alternaria species causing black spot of cabbage are notably different in their basal culture conditions.