BIOLOGICAL CONTROL OF WHITE ROT OF ONION .2. EFFECTIVENESS OF PENICILLIUM NIGRICANS (BAIN) THOM

A study has been made of the persistence of the effects of Penicillium nigricans, in garden loam, on the control of white rot disease of onion. Twenty days old cultures of P. nigricans, diluted up to 0.25 strength, remained effective up to 5 days. Further additions of maize meal to the soil prolonged its effectiveness. The control of white rot was associated with a concentration of 80 μg of griseofulvin per g of soil. Loss of activity in controlling white rot was related to decline in griseofulvin concentration, which in turn was associated with the build of Pseudomonas sp. in soil. Pseudomonas had no effect on S. cepivorum. Decline in control by P. nigricans was followed by a second period of control which was related to increase in number of bacteria antogonistic to S. cepivorum. In agar culture griseofulvin produced a fungistatic effect on the growth of S. cepivorum. Similarly in the presence of griseofulvin in soil, the appearance of white rot infection was delayed. Evidence was obtained to the fact that a fungistatic effect on S. cepivorum is effected by griseofulvin, complete control of white rot was related to increase in population of microorganisms antagonistic to S. cepivorum. © 1969 Dr. W. Junk N.V.