DNA Plasmids and Pathogenicity in Phytopathogenic Fungi

Abstract

One of the exciting applications of the genetic engineering technique is the biological control of plant diseases. Although plasmids are easily found in prokaryotes, only a few examples of plasmids are known in eukaryotes. There are even fewer experimental data on the presence of plasmids in phytopathogenic fungi. Nevertheless, some genetic and molecular evidences accumulated to date encourage further study on plasmids in phytopathogenic fungi. We searched for plasmids among three weakly pathogenic isolates of Rhizoctonia solani and identified a linear DNA plasmid, pRS64 (molecular weight 1.68±0.06x10^6). Weakly pathogenic isolates containing the pRS64 plasmid showed abnormally slow growth and low virulence to Japanese radish seedlings, whereas pathogenic isolates which lacked the plasmid showed normal growth and high virulence. Thus, it is highly probable that the weakly pathogenic character of R. solani isolates is under the control of the pRS64 plasmid, and this mechanism seems to be a clue for the biological control of damping-off of Japanese radish seedlings. Some of the difficulties are outlined that must be surmounted before biological control of plant diseases can be achieved.