A synthetic microbial community for the control of Fusarium wilt of banana

Banana is the most produced fruit in the world. More than 150 million tons of bananas and plantains are produced annually for a business affair of 38.5 billion dollars. The entire banana industry has been threatening by Fusarium oxysporum f. sp. cubense (Foc) tropical race 4 (TR4), which is spreading alarmingly in the cultivation area of banana. We evaluated new biological control agents against Fusarium wilt of banana (FWB) to be used in mixture rather than as single strains. Pseudomonas spp., Bacillus spp., Streptomyces spp. and Trichoderma spp. were isolated from rhizosphere soils of banana crops in Tenerife island and selected for the in vitro antagonism against Foc. Effective strains were used to construct two synthetic microbial communities: SynCom1.0, composed of 44 strains (11 per taxon), and SynCom1.1, composed of 7 strains (Pseudomonas spp. strains P1A1, P1C1, and PS5, Bacillus spp. strains BN8.2 and BT1, Streptomyces sp. strain St2AOB1, and Trichoderma sp. strain T2C1.4). In a pot-experiment, inocula of SynCom1.0's member strains were produced individually and then mixed equally for the soil inoculation, which was made at transplanting. In the soil, SynCom1.0's member strains proliferated throughout the experiment and, at 35 days post-inoculation, they reduced FWB incidence by 22% and symptom severity by 33% (from a value of 3 to 2 on a 0-4 scale). Also, they mitigated the leaf chlorophyll content depletion due to the disease. With the same application protocol, SynCom1.1 decreased symptom severity by 34% (from 2.9 to 1.9), but it did not affect FWB incidence. Both microbial consortia did not suppress significantly Foc in the soil, suggesting biocontrol mechanisms other than the direct antagonism against the pathogen. In vitro assays revealed that, besides the antagonism against Foc, most SynCom's member strains can antagonize each other, especially at the inter-species level, and that Foc can even antagonize the beneficial microbes. However, based on these data, we were able to design a new SynCom (SynCom1.2) composed of three members (Pseudomonas sp. strain PS5, Bacillus sp. strain BN8.2, and Trichoderma sp. strain T2C1.4) that are both cross-compatible and resistant to Foc. SynCom1.2 was better than the previous two consortia in controlling FWB, indicating that inconsistent biocontrol obtained with mere combinations of microbes can be significantly improved by designing a tailor-made synthetic microbial community.