Seed-borne fungi on genebank-stored cruciferous seeds from Japan

A total of 2160 cruciferous seeds stored in the National Institute of Agrobiological Sciences Genebank in Japan were evaluated for the presence of seed-borne fungi and their impacts on seed germination examined. We isolated 1598 fungal cultures belonging to 21 genera from seeds of cruciferous plants (Japanese radish, broccoli, cabbage, kale and Chinese cabbage). Alternaria spp. were commonly found (706 isolates in total), but the dominant species differed among plant species and with the length of storage of the seeds. On Japanese radish and Brassica oleracea seeds, Alternaria brassicicola was frequently detected (19.5 and 11.5 isolates / seed sample, respectively); A. japonica was absent on B. oleracea seeds. In contrast, A. japonica and A. alternata were more commonly (1.9 and 16.8 isolates) detected on Chinese cabbage than on B. oleracea. A. brassicicola and A. japonica apparently inhibited seed germination and caused seed rot. Moreover, Fusarium spp. and Rhizopus stolonifer on Japanese radish seeds and Curvularia inaequalis on cabbage seeds were germination inhibitors. These results suggest that cruciferous germplasm seed lots are frequently affected by pathogenic fungi and especially by Alternaria spp. Seed treatment before storage can be recommended to avoid seed-borne dispersal of fungal diseases and seed infection during seed production.