Identification and application of biocontrol agents against Cotton leaf curl virus disease in Gossypium hirsutumunder greenhouse conditions

ABSTRACTBiological control is a novel approach in crop protection. Bacteria, such as Bacillusspp. and Pseudomonasspp., are reported for this purpose and some of their products are already commercially available. In this study, the rhizosphere and phyllosphere of healthy cotton plants were used as a source of bacterial isolates with properties of potential biocontrol agents. The isolates were screened for phosphate solubilization activity, indole acetic acid (IAA) production and antifungal activity. Two isolates, S1HL3and S1HL4, showed phosphate solubilization and IAA production simultaneously, while another two, JS2HR4and JS3HR2, demonstrated potential to inhibit fungal pathogens. These bacteria were identified as Pseudomonasaeruginosa(S1HL3), Burkholderiasp. (S1HL4) and Bacillussp. (JS2HR4and JS3HR2) based on biochemical and molecular characteristics. The isolates were tested against Cotton leaf curl virus (CLCuV) in greenhouse conditions, both as individual bacterial isolates and consortia. Treated plants were healthy as compared to control plants, where up to 74% of the plants were symptomatic for CLCuV infection. Maximum inhibition of CLCuV was observed in the plants treated with a mixture of bacterial isolates: the viral load in the treated plants was only 0.4% vs. up to 74% in controls. This treatment consortium included P.aeruginosaS1HL3, Burkholderiasp. S1HL4and Bacillusspp. isolates, JS2HR4and JS3HR2. The principal-component biplot showed a highly significant correlation between the viral load percentage and the disease incidence.