Effect of Gliocladium and Trichoderma on damping-off and blight of snapbean caused by Sclerotium rolfsii in the greenhouse

Aqueous suspensions of conidia of 285 wild-type strains and mutants of Gliocladium virens, Trichoderma hamatum, T. harzianum and T. viride were tested against Sclerotium rolfsii in the greenhouse. Ten strains of G. virens and four strains of T. harzianum suppressed damping-off of snapbean by 30-50% and blight by 36-74%. All strains of T. hamatum and T. viride tested as conidia were ineffective. In general, strains of G. virens were more effective in suppressing disease in the greenhouse than strains of T. harzianum. Several strains of G. virens and T. harzianum used alone were equal to or more effective than double and triple mixtures of such strains in disease suppression. Of four formulations of G. virens tested, germlings, alginate-bran-fermenter biomass pellets, and Pyrax-fermenter biomass mixtures reduced disease considerably and all three formulations were more effective than conidia in aqueous suspension. Strain G1-3 of G. virens added to soil as Pyrax-fermenter biomass mixtures in amounts to provide colony-forming units ranging from 1 -5 × 10³ to 1 -2 × 10⁴ per g soil provided statistically significant protection of the host at all concentrations. The extent of biological control with strains G1-3 and G1-21 of G. virens also depended on the strain of the pathogen used. Both strains effectively suppressed disease caused by strain Sr-1 (small sclerotia) of S. rolfsii. They were partially effective against strain Sr-116 (medium size sclerotia) and ineffective against strain Sr-3 (large sclerotia). Although strains G1-3 and G1-21 colonized the sclerotia of all three strains of S. rolfsii in soil effectively, they only reduced germinability of sclerotia of strain Sr-1.