Volume 26, Issue 3
September 1947, pages 77-124
pp 77-92 September 1947
A species ofFusarium was found parasitising pupae ofEpipyrops which in its larval stage is a parasite onPyrilla, a pest of sugarcane.
A remarkable variability between the isolates of the fungus was noticed. One set of isolates produced only microconidia in culture, while the rest of the cultures produced both micro- and macro-conidia. In the natural state both the micro- and macro-conidia were present.
The morphological features are given in detail.
The conidial character bring the culture producing only the microconidia nearest toF. moniliforme (Sheld.) var.subglutinans but blue sclerotia, however, are absent. But as this is stated to be a variable character in literature the fungus is regarded asFusarium moniliforme var.subglutinans.
pp 93-107 September 1947
Brief accounts of the literature dealing with the fungiSclerotium cepivorum Berk, andSclerotium tuliparum Klebahn are given.
Morphology of the two fungi has been described. The only spores produced byS. cepivorum are microconidia on certain media only. Attempts to germinate these microconidia almost uniformly failed as only 14 spores altogether germinated on 20 per cent, tulip juice.
A comparative cultural study ofS. cepivorum andS. tuliparum showed that while both grew well on a great variety of media, nevertheless there was in the case of each a certain amount of specific reaction to the juice of its own host plant. In particular, crude onion juice is markedly inhibitory to the growth ofS. tuliparum. Boiling of the juice largely removes this effect.S. cepivorum does not grow well in tulip juice, boiled or unboiled.
Sclerotium cepivorum is favoured by an acid reaction of the culture medium whileSclerotium tuliparum by a neutral or slightly alkaline reaction.
The temperature range of growth for both fungi is approximately l°-35° C., with an optimum near 20° C.
There is no significant difference by light factor either in growth rate or in the general appearance of the cultures of the two fungi.
pp 108-116 September 1947
Symptoms on the natural hosts and the modes of infection ofS. cepivorum andS. tuliparum are described. WhileS. 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.
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.
Under conditions which were sufficiently favourable to enableS. tuliparum to produce nearly 100 per cent, infection on tulips,S. cepivorum had no ascertainable effect whatsoever.
NeitherS. cepivorum norS. tuliparum is able to attack the host of the other.
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.
It was noticed with both fungi that moist atmospheric conditions and autoclaved soil increased the pathogenicity on almost all the hosts.
pp 117-124 September 1947
Sclerotium cepivorum andSclerotium tuliparum both were found to excrete pectinase enzyme on a variety of media.
Sclerotium cepivorum gave more active preparations of this enzyme when grown on onion than on tulip tissue, and the converse was true forS. tuliparum.
There was evidence that tulip tissue was specifically more sensitive to the enzyme ofS. tuliparum than to that ofS. cepivorum and conversely.
The enzyme prepared fromS. cepivorum was more tolerant of acidity than that ofS. tuliparum.