EFFECT OF PEAT-BRAN INOCULUM OF TRICHODERMA SPECIES ON BIOLOGICAL-CONTROL OF RHIZOCTONIA-SOLANI IN LETTUCE

A range of known biocontrol or plant growth-stimulating species of Trichoderma or Gliocladium were grown on peat-bran substrate to yield between 5 X 10(7)-3 X 10(10) colony forming units (cfu's)g-1 substrate after 14 days growth. Inocula were incorporated into peat:sand potting compost infested with Rhizoctonia solani to give 7-8 X 10(4) cfu's of antagonist g-1 compost and assessed for biological control activity using lettuce seedlings. Six of the eight antagonists decreased damping-off and three of these consistently increased yield in comparison with R. solani treatment alone. Subsequently, peat-bran inoculum of T. harzianum isolate TH1 was incorporated at 0.5% w/v into R. solani infested potting compost. Both autoclaved and nonautoclaved inoculum of T. harzianum TH1 decreased disease and increased yield. Incorporation of ethyl acetate-extracted autoclaved inoculum of T. harzianum TH1 resulted in similar levels of biocontrol and improved plant growth as did incorporation of nonautoclaved and autoclaved T. harzianum TH1 inoculum. The need to standardize inocula and controls is emphasized.