Biocontrol adeptness of bacterial endophytes antagonistic to Colletotrichum spp. causing Colletotrichum leaf disease in rubber (Hevea brasiliensis) and harnessing its plant growth-promoting traits

Abstract

Colletotrichum Leaf Disease (CLD) is one of the major leaf diseases which significantly affect growth and yield of natural rubber (NR). Development of eco-friendly disease management strategies is the need of the hour as various commercial fungicides are banned due to their detrimental effect on environment. The present study characterized antagonistic activities and plant growth promoting properties of five bacterial endophytes, isolated from rubber leaves and roots, against Colletotrichum acutatum and C. gloeosporioides, causing CLD in rubber. In the dual culture test, Bacillus sp. and Stenotrophomonas sp. showed 62 and 60 per cent inhibition of radial growth (PIRG). With the culture filtrate, Stenotrophomonas sp. (RLR1), Bacillus sp. (RRF1), B. subtilis (RLF1), Ochrobactrum anthropi (RLF3), and Burkholderia lata (RLF15) recorded suppression of growth up to 100%. These endophytic bacterial strains were identified based on biochemical characteristics and through 16S rRNA gene sequencing. The isolates were also tested for twenty five plant growth promoting traits. All five isolates responded positively for cellulase production, siderophore production, citrate utilization, and oxidase production. However, all five strains responded negatively to chitinase, urease, phosphate solubilisation, hydrogen sulphide production, and fluorescent pigment production. These results confirmed that the five identified bacterial isolates possessing growth-promoting characteristics have the potential to be used as biocontrol agents against Colletotrichum spp., a major devastating pathogen of rubber.