Unlocking the diversity of microorganisms around banana roots

The human body hosts trillions of microorganisms both inside and on the skin. Many of them are beneficial and help in the digestion of food, making vitamins, and boosting the body’s immune systems, among other things. Similarly, for plants, the soils around the roots host diverse microorganisms, some of which are beneficial to the plants, including strengthening their resistance to diseases and pests.

A team at IITA is unraveling the diversity of microorganisms found in the soils and around the roots of banana plants that are healthy and infected with the deadly Fusarium wilt of banana, also called Panama disease.

This study is part of efforts to tap into the beneficial microorganisms to aid in controlling this deadly disease threatening banana production in sub-Saharan Africa (SSA) and, in turn, the food security and income of millions of farmers.

Panama disease is caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc). There are four strains of the disease, Foc races 1–4. Soil-borne race 1 is present everywhere in sub-Saharan Africa, whereas the deadlier Foc race 4 (TR4) is present only in Mozambique. There are fears that it will spread to other parts of the continent with devastating consequences. Foc race 1 kills some dessert bananas like Sukali Ndizi, Silk, and Gros Michel, while TR4 kills the Cavendish banana as well. There are no effective fungicides or other chemicals for its control.

The research team found that bacterial and fungal communities present in roots and corms were colonized from the rhizosphere—the thin soil layer adhering to the roots. Also, banana plants selectively promote colonization or establishment by specific bacterial and fungal communities from the rhizosphere.

The team identified 129 bacterial and 37 fungal genera of known taxa, including some well-known beneficial strains. These included Actinomycetales, which are known to produce various metabolic compounds that help to suppress various plant and soil-borne pathogens. Others were Pseudomonadales, well known to be responsible for beneficial plant-microbe interactions, and Streptomycetaceae, which are known to produce antagonistic compounds against various plant pathogens.

This is the first study to describe an inventory of bacterial and fungal communities associated with the components of asymptomatic and symptomatic banana plants infected by Foc race 1. The findings were published in the paper Unlocking the Microbiome Communities of Banana (Musa spp.) under Disease Stressed (Fusarium wilt) and Non-Stressed Conditions in Plant Microorganisms MDPI (https://doi.org/10.3390/microorganisms8030443) on 20 March 2020.

This study demonstrates the complexity of bacterial and fungal communities, which possibly interact among themselves (microbe–microbe) and with the banana (host–microbe interactions).

“These cross talks may affect banana plant growth, but they may also result in induced resistance. It is, therefore, useful to study the banana microbiome in commercial plantations where banana plants are treated with inorganic fertilizers and pesticides and compare these communities with our findings to reduce Fusarium infection in commercial plantations,” says Manoj Kaushal, a CGIAR Systems Agronomist with IITA-Tanzania.

The study builds on an earlier one by the same team that was able to establish a correlation between the level of microbiome diversity with the resistance to pathogen invasions in banana roots published in Plants (https://doi.org/10.3390/plants9020263) on 18 February 2020.

The IITA banana research program aims to improve soil health and increase the yields of the East African Highland bananas in a more sustainable way.  The work is supported by the CGIAR Fund and, in particular,  the CGIAR Research Program on Roots, Tubers, and Bananas (CRP-RTB) and the EU under the MUSA2020 project grant agreement (GA) 727624.