1992 Volume 58 Issue 5 Pages 734-740
Attempts were made to examine whether the strawberry pathotype of A. alternata could inhabit in the orchards of Japanese pear cv. Nijisseiki as a causal agent of black spot of the pear. First, black necrotic lesions that naturally occurred on Nijisseiki leaves were collected from the 3 pear orchards in Aichi Prefecture in 1983 and 1984. Field isolates from the 1219 lesions were assayed for their pathogenicity to leaves of Japanese pear and strawberry, but no isolate identified as the strawberry pathotype was detected. Secondly, the pathogen-free nursery plants of strawberry cv. Morioka-16, which were from the meristem-tip cultures, were transplanted in a Nijisseiki pear orchard as effective traps of air-borne spores of the strawberry pathotype during May, 1983 to September, 1984. From lesions that appeared on some leaves of the strawberry plants, an Alternaria fungus was isolated and identified as the strawberry pathotype, suggesting that the strawberry pathotype is inhabiting in Nijisseiki pear orchards at much lower density than the Japanese pear pathotype. In a simulation model experiment, parasitic fitness of the two pathotypes to the pear leaves was compared using highly virulent strains of the respective pathotypes. The results showed that the strawberry pathotype was inferior to the Japanese pear pathotype in parasitic fitness, judged by lesion number and lesion size, on the pear leaves under laboratory, phytotron and field conditions.