Use of Coniothyrium minitans and Gliocladium virens for Biological Control of Sclerotinia sclerotiorum in Glasshouse Lettuce

Coniothyrium minitans and Gliocladium virens, applied separately as solid substrate inocula to soil before planting, significantly reduced infection of lettuce caused by Sclerotinia sclerotiorum. Spore sprays of the antagonist applied to crop residues significantly reduced infection in a subsequent crop. However, as disease levels increased, spore sprays on residues of two subsequent crops did not provide significant control of infection. Increasing the application rate of solid substrate inocula of the antagonists by fivefold to 3.0 liters m−2 did not reduce infection compared with the standard inoculum application rate. Combining preplanting applications of solid substrate inocula of both C. minitans and G. virens gave no increase in control of infection provided by C. minitans alone. Over 80% of sclerotia recovered from plots treated with C. minitans were always infected by the antagonist, which also spread to other plots. In contrast, G. virens infected a maximum of 15% of sclerotia after infecting an initial crop and, in the first two experiments, declined to less than 1% by the third or fourth crop. Only treatments containing C. minitans resulted in a reduction in the number and viability of sclerotia. In vitro infection tests showed that C. minitans infected sclerotia in soil at a lower temperature (4-25°C) than G. virens (10-30°C), which could be the reason for poorer disease control with G. virens in the glasshouse.