Biocontrol solutions to “Fusarium wilt of banana” emerge

The banana crop and industry has experienced extreme losses due to an epidemic of Fusarium wilt of banana (FWB), caused by Fusarium oxysporum  f.sp. cubense (Foc). This was described in the recently published article “Biological control agents against Fusarium wilt of banana.”

FWB, also known as Panama disease, has plagued countries in Africa, Asia, and Australia. The disease is particularly difficult to control for several reasons including being a soilborne fungus with a long survival rate in the soil (more than 20 years), even in the absence of plant hosts, or within alternate hosts, which do not necessarily show disease symptoms. Among other reasons, it is also a vascular pathogen, which escapes contact with control agents once it penetrates the plant.

Africa has had some cases of classical biocontrol successes, one of which was the use of biocontrol for cassava mealybug that reduced losses by over 90%. This initiative was led by IITA. Many interventions have been put in place by the Institute and partners, including Food and Agricultural Organization of the United Nations (FAO) and FAO’s World Banana Forum, to prevent the spread of FWB. These interventions include the Global Program on the Banana Fusarium Wilt Disease and ProMusa International Banana Symposium.

Plant diseases are usually managed by integrated frameworks with an emphasis on preventive measures, especially in the absence of highly effective control means. This is particularly true for soilborne diseases like FWB and Verticillium wilts, with causal pathogens that cannot be eradicated once they contaminate the soil.

A higher FWB incidence has been associated with low soil pH, but such an observation has not been reproduced experimentally. Also, ammonia fumigation and biofertilization have been reported to reduce FWB incidence in a pot experiment, with concurrent increases in soil pH, nutrient contents, and beneficial microbial community. Although no clear experimental evidence exists about the effectiveness against FWB of raising soil pH, it is known that Foc prefers low pH.

A suggested solution to the invasion of FWB is adequate irrigation and fertilization regimes, as well as monthly treatments with zinc sulfate. Waterlogging and acidification of nutritive solutions should be generally avoided.

Also, crop rotation has provided attractive results in some cases. Lower disease control levels have been obtained by using rotations with maize, sugarcane, sunflower, or eggplant.

Biological control and host genetic resistance have been considered the most important strategies for the management of FWB. Findings of this research suggest that biocontrol can greatly limit the damage caused by FWB. However, biocontrol should not be considered as an independent tool, but adequately implemented in an integrated management framework.

Studies have shown that combinations of biocontrol organisms with silicon and mulching, or with neem cake can be advantageous compared to the individual applications, and therefore can provide a better control option for banana growers who have to deal with FWB in their plantations.

The research recommends that more efforts be put in place to further validate currently available outcomes, to deepen the knowledge on the most valuable biological control agents, and to improve their efficacy by setting up effective formulations, application protocols, and integrated strategies.

This article was published in volume 10 of Frontiers in Microbiology – Open access Journal. Find the full article here https://doi.org/10.3389/fmicb.2019.00616