Studies on sclerotium-forming fungi: I. Sclerotium cepivorum Berk and S. tuliparum Klebahn Part 2. Symptoms, mode of infection and host range

Abstract

1. Symptoms on the natural hosts and the modes of infection of S. cepivorum and S. tuliparum are described. While S. cepivorum appears to be able to penetrate the surface of uninjured roots, it does so relatively slowly and uncertainly whereas it freely enters at the stem base. The port of entry has been found the natural wound caused by the emerging root. In case ofS. tuliparum it was the shoot bases and not the roots which were attacked. 2. S. cepivorum is able to attack onion seedlings over the whole range of soil moisture at which ready germination takes place-the greatest development of the disease being near about 40 to 60 per cent, soil moisture. As regards temperature effect, the optimum attack is somewhere in the neighbourhood of 13° to 18° C. 3. Under conditions which were sufficiently favourable to enable S. tuliparum to produce nearly 100 per cent, infection on tulips, S. cepivorum had no ascertainable effect whatsoever. 4. Neither S. cepivorum nor S. tuliparum is able to attack the host of the other. 5. S. tuliparum caused 80-100 per cent, infection of Tulips, Scilla sibirica, Hyacinth, Chionodoxa luciliœ, Iris hispanica; 40-60 per cent, of Gladiolus, Narcissus, Daffodil, Crocus, Snowdrop; 20 per cent, of rhizomes of winter Aconite; and produced no attack on onions, shallots and leek.S. cepivorum on the other hand attacked vigorously most of the onion types, leeks, shallots and red-onions only up to an extent of 20-25 per cent., while it could not attack the hosts ofS. tuliparum. 6. It was noticed with both fungi that moist atmospheric conditions and autoclaved soil increased the pathogenicity on almost all the hosts.