Isolation and identification of Pink-Pigmented Facultative Methylotrophs (PPFMs) and evaluation of their potential as biocontrol agents against Colletotrichum lindemuthianum causing anthracnose of cowpea (Vigna unguiculata L.)

Abstract

Anthracnose caused by Colletotrichum lindemuthianum is a major disease, lead to substantial yield loss of cowpea. Pink-pigmented facultative methylotrophs are a group of aerobic facultative methylotrophic, Gram negative, rod shaped bacteria comes under the genus Methylobacterium. They colonise the phyllosphere and rhizosphere of many plants, interact with them, thus promote growth and suppress plant diseases. This study aimed to isolate PPFMs from cowpea phyllosphere, identify them morphologically and molecularly, and evaluate their biocontrol potential against anthracnose pathogen C. lindemuthianum. Isolation was carried out by leaf imprint method on ammonium‐mineral salts medium supplemented with 0.5% methanol. Typical pink coloured colonies were observed five to seven days after inoculation. Selected 10 PPFM isolates were subjected for biochemical, morphological and molecular characterization via 16S rRNA gene sequencing. in vitro antagonism studies showed that PPFM 8 has strong antagonistic potential, inhibited mycelial growth of C. lindemuthinum with 58.27% inhibition. Further, 16S rRNA gene sequence showing 99.93% identity with Methylorubrum populi. Comparative evaluation of PPFM isolate and biocontrol agents against C. lindemuthianum revealed that T. asperellum significantly inhibited the radial mycelial growth followed by PPFM 8 with 58.65% inhibition. These findings demonstrate that PPFMs are promising candidates for sustainable management of anthracnose in cowpea, warranting further field validation and formulation development.