Abstract
A 2-year field study at Beltsville, MD, of soil artificially infested with sclerotia of Sclerotium rolfsii strain Sr-1 demonstrated the ability of fermentor-produced biomass of Gliocladium virens isolate Gl-3 in 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 Gl-3 per g of soil in the treatment plots were 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 104 CFU of Gl-3 per g of soil significantly increased plant stands after 35 days, compared with 7 and 19% stands in the pathogen-infested control soils for 1992 and 1993, 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 (>85%) in the noninfested control plots. In 1993, although there was no significant correlation (r 2 = 0.601) between rate of amendment and plant stand, all rates gave stands greater than that in the infested control but not as great as that in the noninfested control. Generally, soil populations of Gl-3 increased by 11 days with higher, but not lower, rates of Pyrax/biomass to about 105 CFU/g soil during both years. Population levels tended to decline after 35 days of plant growth, but generally remained higher than the amounts added. This population increase suggested establishment of Gl-3 in the soil. A study to determine the influence of Pyrax and biomass of various isolates of Trichoderma spp. and G. virens on the germination of sclerotia of two S. rolfsii isolates (Sr-1 and Sr-3) indicated considerable specificity. G. virens isolates were more effective in reducing sclerotial germination than 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 sclerotia than those of Sr-1, was less affected by the various isolates of Trichoderma spp. and G. virens than was Sr-1.
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