Characterization of a native Bacillus velezensis-like strain for the potential biocontrol of tropical fruit pathogens

Postharvest fungal decay causes economic loss and may cause human intoxication. Biological control of fungal decay of fruits using antagonistic native bacteria is a promising alternative. Leaf-associated (phyllosphere) bacteria are a promising yet underexploited source of antagonists for fungal control. A total of 108 bacterial isolates from mango (Mangifera indica L.) leaves from orchards in the Campeche state (southern Mexico) were isolated on PDA medium and screened to determine their in vitro antifungal activity against Colletotrichum gloeosporioides var. minor ATTC 42374. Selected antagonistic isolates TS3B-44, TS3B-45, TS3B-92 and TS3B-183 were subject to a comparative analysis to determine their in vitro control potential. The most effective isolate was TS3B-45, identified by 16S rDNA sequencing as being more closely related to Bacillus velezensis; its effect was compared with different control methods: chitosan, two synthetic fungicides (benomyl and prochloraz), NaHCO3 and Bacillus subtilis ATCC 55614. TS3B-45 isolate showed inhibitory activity in vitro (80%), similar to prochloraz (82%) and B. subtilis ATCC 55614 (77%). It also proved effective against other fungal plant pathogens, including native Colletotrichum spp., Colletotrichum gloeosporioides, Curvularia clavata, Pestalotiopsis maculans, and both Fusarium nivale and F. solani. In vivo tests validated the effectiveness of this novel B. velezensis strain against C. gloeosporioides under semi-commercial postharvest conditions, achieving a disease control based on Abbott's method. Based on this analysis, the results did not differ significantly of those exhibited by the commercial product Serenade (R) (Bacillus subtilis). B. velezensis TS3B-45 treatment did not affect a range of quality parameters including maturity index, fruit weight, reducing sugar, and acidity of mangoes after 32 days of storage and shelf conditions. To our knowledge this is the first report of a B. velezensis-like bacterium as a promising suitable biocontrol agent for postharvest conservation. Further testing is required including stabilization, bioformulation and assessment of toxicity against human.