立枯丝核菌的衰退及其生防潜能的研究

THE DECLINE OF RHIZOCTONIA SOLANI KUHN AND ITS POTENTIAL IN BIOLOGICAL CONTROL

A declined strain R-ld of Rhizoctonia solani was obtained from the healthy one R-1(AG-4), which was isolated from the diseased cotton seedling, by routine transfer. The cultural characteristics of R-ld are a slow growth rate, thin hypha and sparce substrate mycelia, light yellowlish eolour, floceose surface texture and production of a few or no sclerotia on the PDA plate. The decline could neither be caused by the bacterial contaminations and the special plasmids of the hypha owing to the results of treating the hypha of R- ld with hot water (52C), the antibiotics and the acridine dyes, nor controlled by the nucleus of R. solani because only 4% of the hyphal tips of R-1d recovered naturally to R-1. The anastomosis between R-ld and R-1 revealed that the decline agent could transmit through fungal fusions to the healthy hypha of R-1. The potting test showed that the pathogenicity of R-ld decreased significantly compared to that of R-1. The disease index was much lower when R-ld was inoculated 2 days before R-1. So R-Id has a high potential in controlling the damping-off of cotton seedlings caused by Rhizoctonia solani.