The influence of formulation onTrichodermabiological activity and frosty pod rot management inTheobroma cacao

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Abstract

Frosty pod rot (FPR), caused by Moniliophthora roreri, is responsible for significant losses in Theobroma cacao. Due to limited options for FPR management, biological control methods using Trichoderma are being studied. Combinations of three formulations and two Trichoderma isolates were studied between May 2009 and April 2011. The formulations were 0·3 mL L−1 of the surfactant BreakThru 100SL (BT), a mixture of 1% w/v Sure-Jell (source of pectin) and 1% w/v potato dextrose broth (PDB) (PP), and an invert oil emulsion of 50% v/v corn oil/2·5% w/v lecithin/0·5% w/v PDB (COP). Water and fungicide, copper oxychloride, were included as controls. Humidity chamber studies indicated that Trichoderma conidia germinated in all formulations if free water was maintained, while only the COP formulation supported germination under drying conditions. In the field, Trichoderma ovalisporum DIS-70a and Trichoderma harzianum DIS-219f were applied monthly in each of the three formulations at a rate of 180 mL per tree, 2·46 × 107 conidia per mL. The COP/DIS-70a formulation provided the largest yield increase compared to all other treatments, including the fungicide control. Averaged over the 2 years, the COP formulation increased yield to 30·7% healthy pods compared to 9·7% healthy pods in the water control. Although the formulation/isolate combinations did not consistently increase endophytic colonization, the PP/DIS-219f, COP/DIS-219f and COP/DIS-70a combinations increased total endophytic/epiphytic colonization by Trichoderma. The invert corn oil formulation of DIS-70a significantly enhanced yield of healthy cacao pods over 2 years providing a promising model for optimizing Trichoderma-based biocontrol strategies.

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