Fungus simultaneously combats two of the main threats to banana productivity

The borer pest and fusariosis disease are among the most important threats to banana trees and their control is still a major challenge for producers. The borer is a beetle commonly known as “banana brat” and causes a direct effect on the rhizome (underground stem capable of emitting branches and roots), weakening the plant's root system, reducing nutrient absorption and causing significant losses of productivity. Adult insects may also play a role in spreading and increasing plant pathogen infections. Fusariosis, also known as “Panama disease”, causes serious yield losses and spreads quickly through various means.

To mitigate its effects, a combination of management practices in commercial plantations is necessary, but it is very important to search for biological control alternatives to complement field management. A fungus still little studied in Brazil and the world that fulfills this role was recently isolated by a group that brings together scientists from the Brazilian Agricultural Research Corporation (Embrapa), the State University of Campinas (Unicamp) and Bioversity International (Colombia), with the support from researchers from the São Paulo Agribusiness Technology Agency (APTA, Vale do Ribeira region) and the Agronomic Institute (IAC). O Beauveria caledonica It was found in the commercial banana production region of Vale do Ribeira, about 190 kilometers southwest of the capital.

Jobs supported by FAPESP and published in Pest Management Science describes the ability of the Beauveria caledonica to infect and kill the banana borer (Cosmopolites sordidus) and to inhibit the phytopathogen Fusarium oxysporum f. sp. cubense (FOC), which causes fusariosis.

“The research demonstrated, for the first time, the dual role of this fungus, isolated from naturally infected banana borers, against the two main phytosanitary restrictions,” says Jeanne Scardini Marinho-Prado, an agronomist with a PhD in entomology from the Federal University of Viçosa and one of the authors of the article. The group proved that, comparatively, isolated from B. caledonica proved to be more efficient in the biocontrol of borer adults than isolates of B. bassiana, a species currently used to biologically combat the insect in the field.

“We isolate B. caledonica of banana borer adults collected in the field and then we made a formulation in emulsifiable vegetable oil, completely biodegradable, with their conidia [spores responsible for asexual reproduction] to increase its effectiveness”, explains Gabriel Moura Mascarin, doctor in insect pathology and microbial control by the Luiz de Queiroz College of Agriculture of the University of São Paulo (Esalq-USP) and by Crop Bioprotection Research (research unit linked to the United States Department of Agriculture).

Formulation

Mascarin is the first author of the work and mainly responsible for the emulsifiable oil formulation evaluated in the article. The oil plays an important role in adhering the fungus to the insect's body, facilitating its infection. The group of scientists also discovered that the fungus produces a secondary compound called oosporin, which had an antagonistic action on the pathogenic fungus FOC. “This antagonistic effect of B. caledonica and its oosporin metabolite on the FOC fungus is unprecedented”, says Prado, who is currently a researcher at Embrapa Meio Ambiente.

Oosporin was detected and quantified using nuclear magnetic resonance and mass spectrometry techniques. In rehearsal vitro against Fusarium, it was found that the acellular filtrates extracted from the fermented broth of B. caledonica containing the oosporin compound exhibited antifungal activity on conidia, resulting in strong inhibition of the germination of the FOC phytopathogen.

“In this study it was demonstrated that certain commercial banana plantations infested by the banana borer can harbor a very specialized community of entomopathogenic fungal species”, says Prado. Soil is an important reservoir of these fungi that can parasitize insects, killing or disabling them. “Therefore, understanding the interaction between C. sordidus and entomopathogenic fungi, in addition to understanding how both can be related to other microorganisms in the soil, is crucial for the development of fungus-based biopesticides”, explains the scientist, highlighting that for now there are no commercial products with B. caledonica.

Also according to the researcher, the development of biopesticides with more virulent strains to the target insect, whether through laboratory selection, formulation, new application strategies or genetic manipulation, can make this microorganism more competitive for use in management programs, thus contributing to more balanced banana growing systems.

The article is written by Mascarin, Prado and Márcia Regina Assalin (Embrapa Meio Ambiente), Lucas Gelin Martins, Erik Sobrinho Braga and Ljubica Tasic (Unicamp), Miguel Dita (Bioversity International, Cali, Colombia) and Rogerio Biaggioni Lopes (Embrapa Genetic Resources and Biotechnology).

The full study Natural occurrence of Beauveria caledonica, pathogenicity to Cosmopolites sordidus and antifungal activity against Fusarium oxysporum f. sp. cubense can be accessed here.