The influence of formulation on Trichoderma biological activity and frosty pod rot disease management in Theobroma cacao

Authors: CROZIER, J - Catie Tropical Agricultural Research; ARROYO, C - Catie Tropical Agricultural Research; MORALES, H - Catie Tropical Agricultural Research; MELNICK, R - Former ARS Employee; Strem, Mary; Collins, Ronald; Bailey, Bryan

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2015
Publication Date: 5/1/2015
Citation: Crozier, J., Arroyo, C., Morales, H., Melnick, R.L., Strem, M.D., Collins, R.T., Bailey, B.A. 2015. The influence of formulation on Trichoderma biological activity and frosty pod rot disease management in Theobroma cacao. Plant Pathology. DOI:10.1111/ppa.12383.

Interpretive Summary: Chocolate is produced from the seeds of the cacao tree. Plant diseases cause significant reductions in yield in all major cacao producing areas of the world, sometime completely destroying the crop. Beneficial fungi are being tested for their potential to reduced cacao disease losses, a management tool known as biological disease control. Fungi, being living organisms, require free moisture and nutrients to survive on above ground parts of the cacao tree (fruits and stems). These above ground plant parts tend to dry out and provide only limited freely available nutrient sources, severely limiting the growth of beneficial fungi. We designed formulations for applying beneficial fungi to above ground parts of the cacao tree, which delay drying and provide nutrients for beneficial fungal growth. The best of these formulations, an invert oil formulation principally composed of corn oil, supported growth of beneficial fungi on the cacao fruit surface and increased yield by more than 3-fold over a two year time period. The invert oil formulation has potential to greatly improve the efficacy of beneficial fungi in managing diseases of cacao. If successful, this new management tool would limit cacao disease losses, improving the lives of cacao farmers, and contribute to stabilization of cacao supplies available to the chocolate industry. This research will be used by cacao farmers and scientists.

Technical Abstract: Frosty pod rot (FPR), caused by Moniliophthora roreri is responsible for significant losses in Theobroma cacao. Due to the 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 of 2009 and April of 2011. The formulations were 0.3 mL L-1 of the surfactant BreakThru 100SL (BT), a mixture of 1% Sure-Jell (source of pectin) and 1% PDB (PP), and an invert oil emulsion of 50% corn oil/2.5% lecithin/0.5% 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 conditions that dried out the other formulations. 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 two years, the COP formulation increased yield to 36.4% healthy pods compared to 10.9% healthy pods in the water control. Formulation/isolate combinations failed to increase endophytic colonization of pods by Trichoderma. The PP/DIS-219f, COP/DIS-219f, and COP/DIS-70a combinations significantly increased total endophytic/epiphytic colonization by Trichoderma. The invert corn oil formulation of DIS-70a significantly enhanced yield of healthy cacao pods over two years providing a promising model for optimizing Trichoderma based biocontrol strategies.