INFLUENCE OF PYRAX BIOMASS OF BIOCONTROL FUNGI ON SNAP BEAN DAMPING-OFF CAUSED BY SCLEROTIUM-ROLFSII IN THE FIELD AND ON GERMINATION OF SCLEROTIA/

A 2-year field study at Beltsville, MD, of soil artificially infested with sclerotia of Sclerotium rolfsii strain Sr-1 demonstrated the abil ity of fermenter-produced biomass of Gliocladium virens isolate G1-3 i n a powder formulation to prevent damping-off of snap beans caused by this pathogen. Plant stands were counted 11 and 35 days after planting . In addition, the CFU of G1-3 per g of soil in the treatment plots we re determined. Pyrax/biomass amended at rates of 15, 30, 60, and 120 g /1.1 m(2) plots to provide 0.6 to 6.6 x 10(4) CFU of G1-3 per g of soi l significantly increased plant stands after 35 days, compared with 7 and 19% stands in the pathogen-infested control soils for 1992 and 199 3, respectively. In 1992, the stand increase was correlated (r(2) = 0. 92) with increased rates of the preparation, such that 60 and 120 g of the Pyrax/biomass per plot resulted in stands comparable to those (>8 5%) in the noninfested control plots. In 1993, although there was no s ignificant correlation (r(2) = 0.601) between rate of amendment and pl ant stand, all rates gave stands greater than that in the infested con trol but not as great as that in the noninfested control. Generally, s oil populations of G1-3 increased by 11 days with higher, but not lowe r, rates of Pyrax/biomass to about 10(5) CFU/g soil during both years. Population levels tended to decline after 35 days of plant growth, bu t generally remained higher than the amounts added. This population in crease suggested establishment of G1-3 in the soil. A study to determi ne the influence of Pyrax and biomass of various isolates of Trichoder ma spp. and G. virens on the germination of sclerotia of two S. rolfsi i isolates (Sr-1 and Sr-3) indicated considerable specificity. G. vire ns isolates were more effective in reducing sclerotial germination tha n were isolates of T. viride, T. hamatum, and T. harzianum. Moreover, isolate G1-3 was more effective that the other G. virens isolates. In addition, S. rolfsii isolate Sr-3, which produces larger and darker sc lerotia than those of Sr-1, was less affected by the various isolates of Trichoderma spp. and G. virens than was Sr-1.