Controle de Phytophthora palmivora, agente causal da podridão-parda dos frutos de cacaueiro com fungos Endofíticos

Abstract

Black pod rot of cacao (Theobroma cacao) is one of the most important diseases affecting the crop worldwide. It is responsible for reducing over than 30% of the cocoa production every year. The disease is caused by Phytophthora spp. being P. palmivora (Butler) Butler one of the most common species in the cocoa growing area of Bahia, Brazil. Fungal endophytes were collected from healthy plants of cacao and cupuaçu (Theobroma grandiflorum (willd. ex Spreng.) Shum. from the states of Amazonas and Bahia, Brazil. The main objectives of this project were to isolate and to select endophytic fungi with biocontrol potential against P. palmivora. Three hundred fungal endophytes were obtained, being 104 screened against P. palmivora based on artificial inoculations of attached pods. Field experiments were performed at Almirante Cacau (Bahia-Brazil). Evaluations of disease severity were possible by using a disease rating scale specifically developed. Eight fungal isolates were selected and tested in the axenic cocoa seedlings for proving the endophytic behavior. From 103 fungi tested in the field, a Trichoderma viride Pers. ex S.F. Gray isolate was selected as the most promising candidate. This fungus was applied on cocoa plants in the field for evaluating its life span in several plant organs. The optimum spore concentration was established and formulation studies for a high performance application were evaluated. The compatibility for a tank mix application with chemical fungicides was tested and also several methods for mass production by solid state fermentation. Studies on the mode of action was carried out by evaluating the production of chitinase, b1,3 glucanase and celulase. With the exception of Tolypocladium sp., all the isolates tested: Three Fusarium, 2 Pestalotiopsis, one Curvularia and T. viride were recovered from the axenic cocoa plants. T. viride on adult cocoa plants showed an efficient epiphytic colonization on the pod surface and inside the trunk as an endophyte, been recovered after 35 and 50 days after application. The disease severity reduced by increasing the inoculum concentration up to 107 conídios.ml-1. The addition of an emulsified vegetable oil was responsible to increase the antagonist efficacy. The T. viride population over the pods decreased after 20 days. After 40 days the fungus was more dificult yor recoveretion. Disease severity increased by decreasing the antagonist population. T. viride germination was not affected by the Cooper hydroxide and Fosetil. A spore concentration of over 108 was achieved using rice as a substrate. The antagonist could grow and secrete b1,3 glucanase and chytinase in all the liquid media tested, however only on media supplemented with carboxymetilcelulose and P. palmivora mycelium were able to induce the production of celulase.