Influence of Pyrax/Biomass of Biocontrol Fungi on Snap Bean Damping-off Caused by Sclerotium rolfsii in the Field and on Germination of Sclerotia. J. A. Lewis, Biocontrol of Plant Diseases Laboratory, Agricultural Research Service, U.S. Department Agriculture, Beltsville, MD 20705. D. R. Fravel, Biocontrol of Plant Diseases Laboratory, Agricultural Research Service, U.S. Department Agriculture, Beltsville, MD 20705. Plant Dis. 80:655. Accepted for publication 1 March 1996. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1996. DOI: 10.1094/PD-80-0655.

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 ll and 35 day's after planting. In addition, the CFU of GI-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 m² 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 (r² = 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 (r² = 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 Gl-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.