Potencial de transmissão do agente causal da murcha de Fusarium da bananeira pela broca-do-rizoma

Abstract

Banana (Musa spp.) is one of the most consumed fruits in the world. It occupies the second place in volume of fruits produced in Brazil. Bahia is currently the largest banana producer in the country. However, phytosanitary constraints can cause significant losses, as is the case of Fusarium wilt, a disease caused by the fungus Fusarium oxysporum f. sp. cubense (Foc). Infection by this pathogen causes destruction of the vascular system, with severe impact on production. It is difficult to eradicate it due to its longevity, since it has the capacity to survive for several years in the soil, being easily disseminated through fungus spores. Presently, the presence of the banana weevil (Cosmopolites sordidus), a widespread insect in all Brazilian banana plantations, has been associated with the causal agent of Fusarium wilt, and in Australia this insect has been related as a vector of tropical race (TR4), a pathogen of quarantine importance for Brazil. Whereas banana weevil, when fed on rhizomes of infected plants, may harbor the spores of the causal agent of the disease in its body, its occurrence may aggravate the disease transmission and may interfere with its management. Two experiments were carried out with the following objectives: (1) to evaluate the potential of transmission of the causal/agent of Fusarium wilt by C. sordidus adults; (2) to determine a possible association between C. sordidus and Fusarium oxysporum f. sp. cubense (3) to evaluate the attractiveness to C. sordidus of different, healthy and infected, banana plant parts regarding to Fusarium wilt. In the first experiment, four banana cultivars (Grande Naine, Maçã, Prata Anã and Princesa) were evaluated as for the infestation by C. sordidus, associated or not with Foc. A completely randomized design was used in a split-plot scheme with ten replicates. The treatments were: 1) control, 2) infection with Foc, 3) infestation by C. sordidus, 4) infestation by C. sordidus + Foc (internally to the insect) and 5) infestation by C. sordidus + Foc (externally to the insect). The evaluated variables (plant height, pseudostem diameter and number of alive leaves) were submitted to analysis of variance and the means were compared by the Tukey test (p <0.05). There was an interaction between C. sordidus and Foc in the different banana cultivars tested by association with the pathogen in the body of the insects. In the second experiment, the attractiveness of rhizome, pseudostem and leaves of banana plants cv. Maçã, healthy and infected by Foc, to C. sordidus females was evaluated. The tests were done in arenas in a completely randomized design with 36 replicates for each part of the plant. In each arena, five females were released. The choice of females was observed after the 30-minute period. The variables evaluated were the number of insects in each of the treatments and the number of insects in the non-response area. The averages of the data were submitted to Student's t test (p<0.05). Females of C. sordidus responded positively to banana pseudostem and rhizome. In turn, the insect was less attracted by the odors of infected plant. This result indicates that the attractiveness of the insect to the plants is mediated by the volatile organic compounds. Knowledge about their behavior can be used to monitor and control the pest. With the existing risk of a possible introduction of Foc TR4, contingency measures should be established, since adults of C. sordidus can carry spores in their exoskeleton or internally, acting as vector of the pathogen.