Biological Control Agents Against Fusarium Wilt of Banana

Abstract

In the last century, the banana crop and industry experienced dramatic losses due to an epidemic of Fusarium wilt of banana (FWB), caused by Fusarium oxysporum f.sp. cubense (Foc) race 1. An even more dramatic menace is now feared due to the spread of Foc tropical race 4. Plant genetic resistance is generally considered as the most plausible strategy for controlling effectively such a devastating disease, as occurred for the first round of FWB epidemic. Nevertheless, with at least 182 articles published since 1970, biological control represents a large body of knowledge on FWB. Remarkably, many studies deal with biological control agents (BCAs) that reached the field-testing stage and even refer to high effectiveness. Some selected BCAs have been repeatedly assayed in independent trials, suggesting their promising value. Overall under field conditions, FWB has been controlled up to 79% by using Pseudomonas spp. strains, and up to 70% by several endophytes and Trichoderma spp. strains. Lower biocontrol efficacy (42-55%) has been obtained with arbuscular mycorrhizal fungi, Bacillus spp., and non-pathogenic Fusarium strains. Studies on Streptomyces spp. have been mostly limited to in vitro conditions so far, with very few pot-experiments, and none conducted in the field. The BCAs have been applied with diverse procedures (e.g., spore suspension, organic amendments, bioformulations, etc.) and at different stages of plant development (i.e., in vitro, nursery, at transplanting, post-transplanting), but there has been no evidence for a protocol better than another. Nonetheless, new bioformulation technologies (e.g., nanotechnology, formulation of microbial consortia and/or their metabolites, etc.) and tailor-made consortia of microbial strains should be encouraged. In conclusion, the literature offers many examples of promising BCAs, suggesting that biocontrol can greatly contribute to limit the damage caused by FWB. More efforts should be done to further validate the currently available outcomes, to deepen the knowledge on the most valuable BCAs, and to improve their efficacy by setting up effective formulations, application protocols, and integrated strategies.

Keywords: Fusarium oxysporum f. sp. cubense; Musa acuminata; Panama disease; beneficial microorganisms; biocontrol; soil microbiota.

Figure 1

Typical symptoms of Fusarium wilt on a banana plant cv. Pequeña Enana (or “Dwarf Cavendish”; AAA genome) in Tenerife.

Figure 2

Control strategies of Fusarium wilt of banana at different epidemic stages. In the absence of Fusarium oxysporum f. sp. cubense (Foc), exclusion measures must be used to prevent the pathogen entrance. At the first incursion of Foc, containment measures must be rapidly initiated. Once Foc is established, containment measures must be continued, and integrated disease management can be adopted. With a high disease prevalence, the use of resistant varieties is the only way to successfully combat FWB.

Figure 3

Main topics of scientific articles dealing with Fusarium wilt of banana. Articles were retrieved from the CAB Direct database (1970–2018) by searching the keywords “Fusarium cubense” or “Panama disease” in the title and abstract. Foc: Fusarium oxysporum f. sp. cubense; FWB: Fusarium wilt of banana; VCGs: vegetative compatibility groups.

Figure 4

Possible modes of action of biological control agents (BCAs). Beneficial microorganisms can exhibit direct antagonism against Fusarium oxysporum f. sp. cubense (Foc) and can affect the plant physiology and/or the microbiota with a consequent, indirect effect against the pathogen.

Figure 5

Effectiveness of biological control agents against Fusarium oxysporum f. sp. cubense (Foc). The dual culture method (A) allows testing the in vitro antifungal activity of metabolites produced by biological control agents (BCAs). Pot experiments (B) provide first evidence for the in planta efficacy of BCAs.

Figure 6

Overview of the efficacy of biological control agents against Fusarium wilt of banana. Data of pot and field trials separated by microbial groups (A) or by Fusarium oxysporum f. sp. cubense (Foc) races (B). Dots correspond to the best control levels (viz. reduction of disease incidence or severity) obtained in each scientific article in the literature. In the boxes, the mean is reported as a cross and the median as a horizontal line.