Evaluación de trichoderma sp. en control de phytophthora. sp., causante de la enfermedad mazorca negra en cacao, a nivel invitro.

Abstract

In Ecuador, cocoa is one of the main commercialization products, both in internal and external demand, being one of the most important production products in the country. It is sought after internationally for its great organoleptic characteristics, both in flavor and aroma, thanks to the unique soil and climatic conditions of the country. The CCN-51 clone, whose main characteristic is its high production and medium resistance to diseases, and the Nacional variety, fine and aromatic, are the most widely cultivated. The most important phytopathogenic diseases are monilla (Moniliophthora roreri), black pod (Phytophthora palmivora) and witches' broom (Moniliophthora perniciosa). Black pod is one of the most limiting diseases in cocoa cultivation, attacking the plant in general, introduced through the roots, until reaching the stem and leaves, usually found in waterlogged soils with poor drainage, The most affected organ is the fruit, since, during the infection in the cob, necrotic spots are produced on the rind, leaving also the kernel white and vain, thus causing a decrease in the quality of the beans, reducing their commercial value and productive yield. Nowadays, the use of beneficial microorganisms as antagonistic agents for the control of fungal diseases has increased. Trichoderma is a biological fungicide, which competes with fungi causing root diseases, with the aim of colonizing the soil, and at the same time is parasitic on phytopathogenic fungi, preventing their growth. The present work was carried out in the laboratory of Plant Health - Environment 2, located in the Faculty of Agricultural Sciences - Technical University of Machala and consisted of applying different treatments based on (Trichoderma harzianum) to evaluate the control of mycelial growth on (Phytophthora sp.) at the level of in vitro culture. For this investigation there were eight treatments used, with five repetitions each one, of which the first four consisted of mixing (Trichoderma harzianum) with the culture medium before plating, so that when solidifying it acts as poisoned food, inoculating the pathogen on it, four different doses were used; 1g/L, 2g/L, 3g/L, 4g/L respectively. In the fifth treatment, the technique of volatile metabolites was used, in which strains of the antagonist and phytopathogen were placed in the center of the base and lid of the petri dish and in the sixth treatment by dual culture (confrontation), strains of the antagonist and the phytopathogen were placed at opposite ends, at the edge of the petri dish. The last two treatments acted as controls, being the seventh the culture of (Phytophthora sp.) and the eighth (Trichoderma harzainum), in which the mycelial growth was identified without competition, to compare it with the other treatments. The treatment that gave the best results was that of volatile metabolites, followed by the dual culture treatment, since these were able to completely inhibit the mycelial growth of the phytopathogen 8 days after its application. When preparing the treatment by poisoned food, the culture medium was heated to boiling point in microwaves, then it was left to cool for an average time of five minutes before adding the Trichoderma strains to mix it with the culture medium, for which reason it did not manage to inhibit the phytopathogen, since, when submitted to high temperatures, instability is caused in the structure of the fungus, diminishing its probability of survival. In view of the favorable results obtained in this research, the need arises to use these methodologies at field level, thus expanding the range of uses of (Trichoderma harzianum.) in the control of mycelial growth of phytopathogenic diseases, raising the immune resistance system of the plant, which would help to increase the productive yield of the cocoa crop.