Seed coating for biocontrol: a sustainable strategy against fungal pathogens in okra and cotton

Bio-coating is a process of coating seed surfaces with plant-beneficial microorganisms, allowing them to colonize plant roots from the very beginning of plant growth to protect the plant from diseases. Okra and cotton seeds were double-coated with biocontrol agents using different polymer combinations to suppress phytopathogens. The bio-coated seeds were evaluated for germination percentage and viability of bioinoculants during storage, and later for plant growth and disease suppression under pot house conditions. Okra coated with Trichoderma asperellum using a lab-prepared combination of chitosan and PVP (Polymer mix- T –Cts-PVP) (Cts: chitosan, PVP: polyvinyl pyrrolidone, T: Trichoderma asperellum) maximally inhibited the growth of Alternaria alternata (73.68%), Rhizoctonia solani (51.80%), and Fusarium oxysporum (48.42%). Similar observations were recorded for cotton seeds coated with Trichoderma asperellum and bacterial consortium (Azotobacter chroococcum HT-54, Bacillus subtilis, Pseudomonas fluorescens, Stenotophomonas maltophilia, and Bacillus megaterium) using carboxymethyl cellulose (CMC) and PVP. All bio-coated seeds showed better germination percentages than the control. All the polymers CMC, chitosan and PVP (polymer mix-T-CMC-PVP and polymer mix-T-Cts-PVP), were more compatible with Trichoderma asperellum than with the bacterial consortium and retained more viable spores for three months on okra seeds. While opposite was observed for cotton seeds and only polymer mix-B-CMC-PVP and polymer mix-T-CMC-PVP were efficient for seed coating. However, with increasing time (90 days after seed coating), the viability of the strains decreased to 5.90 log CFU g⁻¹ on the seed surface. Coated seeds showed resistance against disease and reduced disease incidence to even 0.00% compared to non-coated seeds under pot experiment. This study provides insights into the potential of seed coating to suppress fungal pathogens.