EVALUATION OF LAETISARIA-ARVALIS AS A BIOLOGICAL-CONTROL AGENT OF RHIZOCTONIA-SOLANI ON WHITE POTATO

Laetisaria arvalis, a soil-inhabiting basidiomycete, reduced Rhizoctomia solani infection of white potato. A greenhouse study that monitored population levels of both fungi showed that soil infested with L. arvalis suppressed the growth of R. solani after eight wks. Populations of L. arvalis and R. solani increased after 11 wks. when both fungi were infested simultaneously and when L. arvalis was introduced to soil previously infested with R. solani. Five years of field studies showed that various L. arvalis seed treatments and soil amendments reduced R. solani infection of stems and stolons and sclerotial formation on tubers equal to the standard chemical treatment of pentachloronitrobenzene (PCNB) + thiabendazole. No relationship was shown between populations of L. arvalis and R. solani in field plot soils, but native or wild strains of L. arvalis were shown to be present at detectable levels in field soils.