Espécies de Fusarium associadas às sementes de feijão-fava: caracterização molecular, potencial toxigênico e controle

Abstract

Phaseolus lunatus L. is one of the four species of the genus Phaseolus most cultivated and produced worldwide. The disease absence and pathogen identification increases the crop vulnerability, with greater risks of economic losses and the difficulty of adequate management strategies. Thermotherapy has shown to be an efficient method for eradicating microorganisms, but it depends on the differential sensitivity to heat stress between seed and pathogen. Thus, the objective of this work was to perform the molecular characterization, toxigenic and pathogenic potential of Fusarium spp. isolates, as well as to evaluate the effect of thermotherapy on the quality of lima bean seeds. It was evaluate thermotherapy effect on seeds of six lima beans varieties: Branca, Cearense, Cara Larga, Orelha de Vó, Roxinha and Orelha de Veia, which were subjected to control treatments (untreated), Captana fungicide (240 g 100 kg-1 of seeds) and humid thermotherapy at 40, 50 and 60 °C for 5 and 10 minutes of immersion. The seeds were carried out to the sanity, germination and emergence tests. A total of 26 isolates of Fusarium spp. associated with the seeds of lima bean varieties were isolated. The molecular fungi characterization was performed using sequences of the TEF1 and RPB2 gene regions. The toxigenic profile of the Fusarium species for detection of the FUM1 gene predictive of fumonisin was determined by molecular method using the primers FUM53F/R and VERTF1/2. Prevalence was obtained by the number of isolates belonging to a species in relation to the number of isolates per variety. The Fusarium spp. pathogenicity was evaluated through inoculating seeds of the Orelha de Vó variety using spore suspension method. The disease index, infection rate, final plant stand, emergence speed index, roots volume of, length and dry mass of the aerial part and roots were determined. Thermotherapy at 40 °C for 5 and 10 minutes was the best results under the conditions tested to reduce the incidence of Aspergillus spp., Fusarium spp. and Penicillium sp., without affecting the seeds physiological quality. The seeds of Branca, Cearense and Orelha de Veia showed greater sensitivity to thermal stress when exposed to humid heat at 60 °C for 10 minutes, with percentage of germination, emergence reduction and an increase in dead seeds. Eleven species of Fusarium were identified: F. hainanense, F. caatingaense, F. lacertarum, F. sulawesiense, F. pernambucanum, F. irregulare, F. verticillioides, F. annulatum, F. napiforme, F. contaminatum and F. fabacearum. This is the first report in the world of the species F. hainanense, F. lacertarum, F. irregulare, F. annulatum, F. napiforme, F. contaminatum and F. fabacearum infecting lima bean seeds. Among the species, F. verticillioides was the most prevalent, being restricted to the varieties Cara Larga, Orelha de Vó and Orelha de Veia. All F. verticillioides isolates and one of F. hainanense showed themselves positive as presence of the FUM1 gene, predictive of fumonisin. The isolates did not affect the physiological parameters of lima bean plants, leading to a series of metabolic and growth dysfunctions.