Use of Coniothyrium minitans and other microorganisms for reducing Sclerotinia sclerotiorum

Abstract

Biological control agents (BCAs) Bacillus subtilis QST 713, Coniothyrium minitans CON/M/91-08, Streptomyces lydicus WYEC 108, and Trichoderma harzianum T-22 were evaluated for their efficacy in the reduction of survival of sclerotia and production of apothecia of Sclerotinia sclerotiorum under controlled environments. A growth chamber assay was conducted where 25 sclerotia were buried in pots containing potting soil, and BCAs were drenched into the soil at various concentrations, and five soybean seeds were planted in each pot. The presence and number of S. sclerotiorum apothecia were recorded daily. Sclerotinia sclerotiorum sclerotia were retrieved six weeks after seeding and viability was assessed on water agar plates. All BCAs were effective in reducing S. sclerotiorum inoculum at various efficacies. In general, efficacy was positively correlated with the rate of application. At the rate of application when the efficacy did not change significantly by increasing the rate, the BCAs had various reductions of apothecia and sclerotia. B. subtilis reduced apothecia and sclerotia by 91.2 and 29.6%, respectively; C. minitans reduced apothecia and sclerotia by 81.2 and 50%, respectively; Streptomyces lydicus reduced apothecia and sclerotia by 100 and 29.6%, respectively; Trichoderma harzianum reduced apothecia and sclerotia by 80.5 and 31.7%, respectively. In addition, the commercial strain of C. minitans CON/M/91-08, and a wild Michigan strain of C. minitans W09 were compared for their growth and sclerotial reduction. W09 had faster growth rate than the commercial strain, indicating potential diversities of biological control strains to be studied.