Fusarium oxysporum f. sp. cubense : hospedeiros alternativos e vetor

Abstract

One of the most important diseases in the banana crop is the Panama disease, or fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. cubense (Foc). Little is known about the role of alternative hosts and a possible vector on the dispersion and persistence of the disease in the field. Thus, the objective of this study was to verify the potential of weeds and plants used as green mulch as alternative hosts of Foc and the role of the banana weevil borer (Cosmopolites sordidus) in the dissemination of the disease. For the study of alternative hosts, weeds collectedar banana plants showing fusarium wilt symptoms were submitted to the isolation of Foc possibly present in tissues of the aerial part and roots. After isolation, those isolates identified as F. oxysporum by sequencing the ITS regions and the gene encoding for TEF-1α were subjected to pathogenicity tests for bananas. In addition, seeds of six species used as mulches were disinfested and sown on substrate infested with Foc. At the end of the experimental period, root and aboveground samples of these plants were collected for reisolation and characterization of the inoculated Foc isolate by PCR reaction. To study the role of banana weevil borer in the dissemination of the disease, adult insects collected in banana plantations contrasting in the presence of FB (Foc+ and Foc-) were analyzed for the presence of Foc spores possibly associated with the exoskeleton or in the digestive tract. After obtaining the isolates, those identified as F. oxysporum were subjected to pathogenicity tests on banana trees. In a second step, adults of C. sordidus were exposed to the inoculum source of Foc and placed in contact with banana seedlings to evaluate its potential as a vector of the disease. Some legumes may serve as alternative hosts for Foc, like Crotalaria spectabilis, Raphanus sativus e Canavalia ensiformis. It was possible to isolate F. oxysporum colonies associated with weeds and the exoskeleton of C. sordidus adults collected in the field. However, when testing for pathogenicity to bananas, it was verified that these were possibly not Foc. When evaluating the dynamics of the interaction between the banana berry borer and the causal agent of Panama disease, it was observed that there might be a fungusinsect association on the incidence and intensity of the disease in bananas.