USE OF CONIOTHYRIUM-MINITANS AND GLIOCLADIUM-VIRENS FOR BIOLOGICAL-CONTROL OF SCLEROTINIA-SCLEROTIORUM IN GLASSHOUSE LETTUCE

Coniothyrium minitans and Gliocladium virens, applied separately as so lid substrate inocula to soil before planting, significantly reduced i nfection of lettuce caused by Sclerotinia sclerotiorum. Spore sprays o f the antagonist applied to crop residues significantly reduced infect ion 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 substr ate 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 bot h C. minitans and G. virens gave no increase in control of infection p rovided by C. minitans alone. Over 80% of sclerotia recovered from plo ts treated with C. minitans were always infected by the antagonist, wh ich also spread to other plots. In contrast, G. virens infected a maxi mum of 15% of sclerotia after infecting an initial crop and, in the fi rst two experiments, declined to less than 1% by the third or fourth c rop, Only treatments containing C. minitans resulted in a reduction in the number and viability of sclerotia, In vitro infection tests showe d that C. minitans infected sclerotia in soil at a lower temperature ( 4-25 degrees C) than G. virens (10-30 degrees C), which could be the r eason for poorer disease control with G. virens in the glasshouse. (C) 1995 Academic Press, Inc.