EFFECTS OF THE MYCOPARASITE VERTICILLIUM-BIGUTTATUM ON BARLEY STUNT DISEASE CAUSED BY RHIZOCTONIA-SOLANI ANASTOMOSIS GROUP-8 IN A MODEL SYSTEM

The height of barley stunted by Rhizoctonia solani anastomosis group 8 was significantly increased by up to 72.8% after incubation for 8 day s at 20 degrees C in seedling tray tests following application of the mycoparasite Verticillium biguttatum. The pathogen and mycoparasite we re applied at the rate of 1% Perlite maizemeal inoculum (w/w potting m ixture) resulting in propagule densities of approximately 24.0 and 6.6 x 10(5) colony-forming units (cfu) per g potting mixture, respectivel y. Sieving (2 mm) R. solani inoculum prior to dilution in potting mixt ure increased the recovery of propagules from 1.2 x 10(3) to 2.1x10(3) cfu per g inoculum compared with recovery when inoculum was sieved af ter dilution. Applications of a V. biguttatum isolate from the UK (vb1 ) and a Dutch isolate (M73) reduced stunting to a similar extent but d id not stimulate the growth of healthy plants. The height of stunted p lants was significantly increased after application of V. biguttatum i noculum after 6 days if inoculated trays were preincubated for 1 day p rior to planting but a similar increase was only detected after 7 days if seeds were planted immediately. The number of stunted plants which emerged after 4 days was significantly increased by treatment with V. biguttatum but preincubation had no additional effect. These results suggested that control of R. solani was effected both before and after the initiation of disease.