Controle biológico da podridão vermelha do sisal (Agave sisalana Perrine) com Trichoderma ssp. e Actinobactérias

Abstract

Sisal stem red rot disease has been causing severe damage to sisal fields in the semiarid region of Brazil. There are very few research studies with this crop and disease control methods have not been described in the literature. Biological control strategies should be studied for control of this disease, which is caused by Aspergillus niger, a soil fungi, with worldwide distribution, and dificult to control. The success of Trichoderma and actinobacteria in biological control studies of plant diseases have been described for several crops of economic importance. However, these studies with sisal are rare. The present work aimed to evaluate the potential of Trichoderma spp. and actinobacteria for control of sisal stem red rot disease, with formulations of Trichoderma and combinations of these formulations and of actinobacteria strains. A total of 55 Trichoderma isolates belonging to seven species, and actinobacteria selected previously from a culture collection of 54 isolates were evaluated. In this study, laboratory results were very diferente from results obtained in field studies, indicating the environmental influence in the interaction plant-microbe-soil. The efficiency of Trichoderma in control of sisal stem red rot disease varied with the isolate and the environmental conditions. T. harzianum (isolate TCS76), T. virens (isolate TCS43), and T. viride (isolate TCS09) promoted a significative reduction in disease incidence and severity, in both environmental conditions. The experiments conducted in soil and sisal residue showed that Trichoderma and actinobacteria were not efficient in reducing A. niger population in soil. Sisal residue fro leaf decortication process, is not an adequate medium for growth and formulation of Trichoderma inoculum. Actinobacteria isolates grew in fresh sisal residue, but did not promote control of A. niger, under in vitro conditions, nor the control of stem red rot disease in field studies with sisal plants. The use of combined isolates of Trichoderma and of actinobacteria did not increase the potential for biocontrol of sisal stem red rot disease.