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Sisal is an economically and socially significant perennial crop for the semiarid region of the world. Bole rot disease, caused by black aspergilli, mainly by Aspergillus welwitschiae, is responsible for great losses due to the ability of the pathogen to kill the plant. The health status of plants that harbor endophytic biocontrol agents (BCAs) is being investigated in this study. We conducted experiments with endophytic bacteria from different parts of healthy and diseased sisal plants to select potential BCAs to control the disease. Studies on the populational densities showed that leaves have less bacteria when compared to roots and stems, and that diseased plants tended to have higher populations of bacterial endophytes. These results were obtained with both conventional plate counting and qPCR. A total of 497 isolates were screened as potential biocontrol agents on sisal discs and nine were selected as having direct antagonistic activity. Five isolates were from healthy and four from diseased plant parts. All these nine isolates significantly decreased the bole rot disease incidence in two field experiments and were identified by sequencing of the 16S rDNA as species belonging in the genera Bacillus, Brevibacterium, Burkholderia (2 isolates), Paenibacillus, Pseudomonas and Serratia (3 isolates). Isolate 466 of Burkholderia lowered 80% of disease incidence in both field experiments, which was not significantly different from the non-inoculated, negative control. We discussed these findings under an ecological-physiological interaction standpoint, as well as the possibilities of including diseased plants in bioprospection strategies and applying the selected isolates in the development of bioproducts.

Witches’ broom is the most devastating disease of cacao in Brazil, and losses to it entail serious socio-economical and environmental problems. Biological control of the causal agent Moniliophthora perniciosa ( Mp ) using the antagonistic fungus Trichoderma stromaticum ( Ts ) is promising, although the identification of superior isolates is necessary. Here, we report a study on the selection of more effective Ts isolates based on field experiments. Sixty-three Ts isolates from a local collection were applied on brooms and placed under typical conditions of shaded-cacao plantations in southeastern Bahia State (Brazil), during two periods of three months each. The percentages of Ts sporulation and incidence and severity of Mp were the parameters used for biocontrol assessments. The results from both experiments were very distinct, indicating a high phenotypic variation in this collection and suggesting a significant effect of the environment in the Ts – Mp interaction. Ts- sporulation rates were negatively correlated with the presence of Mp in the brooms and a number of isolates reduced Mp incidence more efficiently than the reference isolate. Contrasting isolates in their efficiency of reducing Mp incidence were selected and further tested in four subsequent field trials for validation purposes. The results partially confirmed their biocontrol phenotypes but also suggested isolate-specific responses to environmental variations. Inhibition of Mp -basidiospore germination by total protein secreted in culture supernatants of Ts isolates correlated well with field results and revealed a potentially useful procedure for pre-screening of large collections towards selection of better biological control isolates. The characteristics and efficiency of the method as a reliable protocol for identification of superior BCAs in the witches’ broom—cacao pathosystem is discussed.

The Black-Pod Rot of cacao (Theobroma cacao) caused by Phytophthora species is one of the most important diseases affecting this crop worldwide, with average annual losses above 30%. The aim of this work was to assess the potential for the endophytic Trichoderma martiale strain ALF 247 to control Phytophthora palmivora. When ALF 247 was applied at concentrations ranging from 1 × 104 to 5 × 107 conidia per milliliter, the disease severity decreased proportionally. Addition of vegetable oil and/or sucrose in the formulations did not affect the biocontrol results. Fungicides such as copper hydroxide and fosetyl-Al had no effect on conidial germination of this T. martiale strain, with the germination percentage maintained above 90%. Once sprayed, the population of T. martiale tended to decrease progressively on the surface of cacao pods (∼30–40 days post-application), with a concomitant increase in the severity of pod disease. Production of 1.02 × 108 conidia g−1 was obtained after culturing ALF 247 on solid substrate (rice grains) supplemented with calcium carbonate. The results indicate a clear-cut potential of the T. martiale ALF 247 to be used for control of Black-Pod Rot of cacao, although further studies are required to render this isolate technically and economically efficient as a biocontrol agent on agronomic scale.