Endophytic Bacillus spp. of coffee plants (Coffea arabica L.) and its potential in the biocontrol of phytopathogenic fungi and Lepidoptera larvae

Abstract

Background

Research with coffee (Coffea arabica L., Rubiaceae) endophytic microorganisms demonstrates that there is a rich microbiota that has diverse abilities to protect plants and act against phytopathogens. Therefore, the isolation and knowledge of endophytic microorganisms are important for future explorations aimed at using promising strains in controlling pests and diseases and promoting plant growth. The present work aimed to: (i) isolate and identify endophytic Bacillus strains from leaves of C. arabica plants; (ii) carry out the morphological and molecular characterization; (iii) evaluate the mycelial inhibition capacity of soil phytopathogens in vitro; (iv) and evaluate the pathogenicity of the strains against the tested lepidopteran insect pests.

Results

As a result, three species of Bacillus were isolated: B. mycoides, B. thuringiensis and B. velezensis. B. thuringiensis was virulent to Spodoptera frugiperda, Helicoverpa armigera, Chrysodeixis includens and Diatraea saccharalis and showed 100% pest mortality, and the lethal concentration (LC₅₀ values) was estimated: 6.78 × 10³ spores/ml to S. frugiperda; 6.23 × 10² spores/ml to H. armigera; 9.28 × 10² spores/ml to C. includens; and 5.81 × 10¹ spores/ml to D. saccharalis. In total, seven genes related to pathogenicity in insects were found in B. thuringiensis based on genome: cry1Ab24, cry1Bd2, cry2Aa9, cry2Ab41, cry1Ea7, cry1Ia37 and Spp1Aa1. Furthermore, B. velezensis was able to inhibit the growth of phytopathogens: Fusarium oxysporum (49%), Rhizoctonia solani (72%) and Macrophomina phaseolina (65%) and provided above 50% mortality on S. frugiperda and C. includens. Regarding B. mycoides, it was not efficient in inhibiting the growth of pathogens and causing pest mortality.

Conclusion

Two (B. thuringiensis and B. velezensis) of three endophytic bacteria isolated from coffee leaves showed potential to use in biological control of important pests and phytopathogens of agriculture, with high mortality of lepidopteran larvae in laboratory with B. thurigiensis and high mycelial inhibition with B. velezensis. More studies with these two strains must be carried out in greenhouse and in field to prove its beneficial properties.