Atividade biocontroladora de Trichoderma spp. e de leveduras sobre Diaporthe destruens

Abstract

The occurrence of foot rot caused by Diaporthe destruens compromises the productivity of sweet potato and poses a threat to the entire production chain of tuber, there are no fungicide registered in the Ministério da Agricultura, Pecuária e Abastecimento (MAPA) for the management of this disease. Biological control, using Trichoderma spp. and yeast, promising antagonist agents, is an efficient solution and can be applied with the crop management. The study aimed to select species of Trichoderma and yeasts with biocontrol potential on Diaporthe destruens. The pathogenicity test was performed with the isolates obtained from diseased branches, selecting the most aggressive for the studies. In vitro antagonism of Trichoderma spp. was evaluated by pairing culture and yeast by pairing culture, compound diffusion and Killer toxin production. In the in vivo tests, sweet potato seedlings, Co-Roxa and Co-Branca varieties, were produced in a greenhouse. For the trials with Trichoderma spp. the treatments were composed of substrate infested with the nine isolates of the antagonist. For the yeast tests, the plants were sprayed by a cell suspension of the selected isolates in vitro. In both testes, the inoculation of the pathogen was carried out through disks, in two distinct regions of the plant. 110 fungal isolates were obtained, in which 60 were pathogenic, selecting the isolate TH9 (Diaporthe destruens) for the tests. Of the 21 isolates of Trichoderma spp. obtained in the study, nine obtained better results in the pairing and three were more efficient in controlling the pathogen in vivo, identifying two species T. longigbrachiatum (013) and T. asperellum (162 and 177). Of the 52 yeasts tested, 15 showed 100% inhibition of the mycelial growth of the pathogen in the diffusion of compounds. In the Killer toxin assays, there was a difference in halo intensity expressed by yeasts. In both varieties, four isolates were efficient in reducing the symptoms of the disease in vivo, identifying two species of yeasts Moesziomyces aphidis (LFB13 and LCB15) and Candida orthopsilosis (LFB22 and LFB25) potentially antagonists. This is the first report of the reduction of the symptoms of foot rot of sweet potato by the antagonistic action of Trichoderma spp., M. aphidis and C. orthopsilosis. These antagonists can be used in the management of the disease.