Efficacy of Selected Biocontrol Agents in Controlling Papaya Leaf Curl Disease

The leaf curl disease of papaya caused by Begomovirus reduces papaya production significantly in Bangladesh and elsewhere. Papaya growers spray chemical insecticide indiscriminately to combat this disease due to the unavailability of appropriate resistant cultivars or effective alternative control approaches. To reduce chemical use, finding suitable eco-friendly methods of leaf curl management is paramount. We evaluated the efficacy of three microbial biocontrol agents, viz. Trichoderma harzianum, Bacillus cereus (Bc), and Bacillus thuringiensis subsp. kurstaki (Btk) to control the leaf curl disease in papaya as well as to improve the growth of papaya. The effect was compared with a chemical insecticide named 'Duel' (Chlorpyrifos 50% + Cypermethrin 5%). Two papaya cultivars, Red Queen and Red Top, were used in this study. Suspension of these bio-agents and solution of the chemical were applied as foliar sprays at 15, 45, 75, and 105 days after transplanting. None of these treatments influenced plant vegetative growth, and size of plants. Among the bioagents, T. harzianum was highly effective in reducing the incidence (15%), and severity (10%) of papaya leaf curl in both cultivars, especially at the mid to later disease stage, i. e. 75-105 DAT, which was found to be more effective than the chemical spray (5% incidence, 3% severity). Again, the Btk but not the Bc treatment showed some effects in reducing the diseases (30% incidence, 10% severity). Intriguingly, T. harzianum treated plants produced a higher number of flowers and fruits in both papaya cultivars. In summary, two microbial biocontrol agents (T. harzianum and Btk) showed promising results in suppressing papaya leaf curl, which could be utilized in papaya orchards to fend off this menace as an effective eco-friendly alternative to harmful chemical pesticides.