Endophytic bacteria isolated from both healthy and diseased Agave sisalana plants are able to control the bole rot disease

Abstract

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.