Fusarium oxysporum isolated from wilted seedlings and diseased bulbs of onion was pathogenic to the seedlings and bulbs of onion and to the seedlings of Welsh onion, but not to other plants. Some other formae speciales of F. oxysporum tested were scarcely pathogenic to onion. Thus the onion isolates were identified to be F. oxysporum f. sp. cepae which is specifically pathogenic to onion and Welsh onion.
