Dual biocontrol strategy: Fluorescent pseudomonads and methylotrophic bacteria in combating Corynespora leaf spot in...

Blackgram leaf spot, caused by Corynespora cassiicola, is a serious disease that significantly reduces global blackgram production. The non-commercial nature of the crop and growing nutritional significance in recent years made it necessary to implement an economical and environmentally responsible disease management strategy. In this line, twenty isolates each of fluorescent pseudomonads (FP) and facultative methylotrophs (FM) were isolated from the black gram phyllosphere. In vitro dual-culture assays demonstrated the potential of FPs (CBP-05, PPP-01) and FMs (PPM-01, ABM-04) to inhibit the mycelial growth of C. cassiicola. Further, 16S rRNA sequencing assigned the potential isolates PPP-01 and CBP-05 to Pseudomonas fluorescens, while the FM isolates PPM-01 and ABM-04 were assigned to Methylobacterium indicum and Hyphomicrobium facile, respectively. The co-culture assay revealed mutual compatibility between FP and FM. An exploration of their possible biocontrol mechanisms revealed key functions such as the production of indole-3-acetic acid, secretion of extracellular enzymes (catalases, amylases, ureases and proteases), hydrogen cyanide synthesis, siderophore production and solubilization of phosphate and potassium. Field tests with foliar spray of the consortium comprising CBP-05, PPP-01, PPM-01 and ABM-04 resulted in the lowest percentage disease index against Corynespora leaf spot (36.37%) along with a marked increase in crop yield comparable to chemical control during two consecutive years (November-April) 2020-21 and 2021-22. This study highlights the potential of a dual-functional FP-FM consortium to enhance plant growth, suppress pathogens, and provide an effective biocontrol solution for Corynespora leaf spot in blackgram.