Elucidating the synergistic activity of biocontrol agents in combating Xanthomonas citri pv. malvacearum and promoting of physio-chemical responses in cotton

Cotton (Gossypium hirsutum L.) is an important fiber crop in agriculture-based economy countries, identifying the yield and quality-limiting factors are the key concerns for cotton growers. In this regard, many abiotic and biotic factors are reported to have a negative impact on cotton quality and eventually impact the textile industry. Bacterial blight of cotton (BBC) caused by Xanthomonas citri pv. malvacearum (X. citri pv. malvacearum) poses a major threat to cotton crops worldwide and epidemics largely depend on suitable environmental conditions. In the present study biocontrol agents Bacillus subtilis, Pseudomonas fluorescens and Trichoderma harzianum were tested individually and in combinations for sustainable control of the BBC of cotton. Among the treatments B. subtilis + P. fluorescens exhibited promising results in controlling BBC incidence (40 %) under field conditions, stimulated plant growth and improved fiber fitness, fiber quality and staple length. In addition to antagonism, these bio-agents triggered defensive enzymes and showed higher activity of peroxidases, phenylalanine ammonia-lyase, polyphenol oxidase, β-1,3 glucanase. However, physiological traits such as transpiration rate, water use efficiency, stomatal conductance, chlorophyll and cell membrane stability were found to be enhanced in B. subtilis + P. fluorescens treated plants. The overall results revealed that combined application of B. subtilis + P. fluorescens could significantly augment plant productivity, reduce BBC disease incidence and trigger physio-chemical attributes, indirectly sustaining plant health and improving fiber traits.