Alternaria on cruciferous plants. 4. Alternaria species on seed of some cruciferous crops and their pathogenicity

The incidence of Alternaria spp. on seed samples of cruciferous vegetable crops was surveyed between 1990 and 1992. Some commercial seed lots of crucifers which are commonly grown in Japan were infested with Altemaria species. Three Alternaria species were encountered on the seed samples of Brassica campestris, B. orelacea, and Raphanus sativus, The most frequently detected species were A. japonica and A. a/ternata on B. campestris, A. brassicicola on B. oleracea, and A, japonica and A. alternata on R. sativus, respectively. Alternaria brassicae was not detected in this study. Alternaria brassicicola isolates from these crops produced necrotic lesions on all of the crucifer seedlings inoculated, while A. japonica induced different reactions in different plants or plant parts depending on isolates used in inoculation tests. In contrast, most isolates of A. alternata could not produce necrotic lesions on foliage leaves of crucifers inoculated, although some of them produced clear lesions only on cotyledons. Alternaria alternata associated with these cruciferous crop seeds was considered to he an oppotunistic parasite of these crops.