Mal-do-pé da batata-doce no Nordeste do Brasil: diversidade de patógenos e controle biológico

Abstract

Foot rot of sweet potato [Ipomoea batatas (L.)] (MP), the main disease that affects the crop in Northeastern Brazil, is caused by fungi of the genus Diaporthe, Nigrospora, Neoscytalidium and Lasiodiplodia and can cause the destruction of the root system, preventing the formation of tuberous storages. Currently there is no registration of fungicides in the Ministério da Agricultura, Pecuária e Abastecimento do Brasil (MAPA), making it difficult to manage MP, requiring the search for alternative methods, such as biological control. This study aimed to identify the species related to MP, evaluate the epidemiological aspects of the disease in sweet potato producing regions in the states of Pernambuco, Paraíba, Sergipe and Alagoas, as well as test the effectiveness of yeasts in the biological control of pathogens. Symptomatic plants were collected for indirect isolation and preservation of the pathogen in the Coleção de Fungos de Solo (CFS), at Laboratório de Fungos de Solo (LAFSOL), at the Universidade Federal Rural de Pernambuco. The species were identified by amplification and sequencing of the Elongation Factor 1-α (tef1-α), Internal Transcribed Space (ITS) and β-tubulin (Tub) regions. Maximum Likelihood Analysis and Bayesian Inference were used to identify the isolates throught the phylogenetic tree obtained by comparing previously described species. After identification of the causal agents of the PM, the biological control of the causal agents with antagonist yeasts, provided by CFS, was evaluated by in vitro tests of joint cultivation and production of volatile compounds, and in vivo, with evaluation of the time of immersion of the seedlings in yeast suspension and molecular identification. The analyzes confirmed the incidence of Diaporthe destruens, D. batates, D. kongii, Macrophomina sp. and Neoscytalidium dimidiatum, in addition to promoting the first report of D. citri and D. ueckeri as causal agents of sweet potato foot disease in the world. The biological control tests indicated that the yeasts Moeszyomices aphidis and Candida orthopsilosis are effective in controlling the disease, in vitro, through control mechanisms, such as antibiosis, parasitism and production of volatile metabolites, and in vivo, with protection of seedlings after different immersion times in the antagonist suspension. The importance of correct identification of pathogens, as well as the discovery of effective methods for managing the disease, is of fundamental importance for the reduction of economic damage generated in the production areas, due to the incidence of the disease.