Drought, Waterlogging and Co-Infection Influence the Severity of Coniella granati and Phytophthora palmivora in Pomegranate and the Biocontrol Efficacy of Bacillus amyloliquefaciens

Cultivation of pomegranate (Punica granatum) is threatened by the emerging pathogens Coniella granati and Phytophthora palmivora. Whether these microorganisms increase their damage due to simultaneous infection and abiotic stress in pomegranate is unknown. Amylo-X LC is an effective biofungicide based on Bacillus amyloliquefaciens but its efficacy to protect pomegranate from C. granati and P. palmivora if plants are under abiotic stress has not been tested. Therefore, the effects of drought, waterlogging and co-infection on the aggressiveness of these two pathogens and the efficacy of Amylo-X LC were evaluated. Pomegranate trees were subjected to regular watering, drought and waterlogging conditions, treated with Amylo-X LC, and individually or simultaneously inoculated in the stem by C. granati and P. palmivora. Drought experienced by trees limited P. palmivora, while waterlogging favoured C. granati. In combined infections, the presence of P. palmivora amplified the damage caused by C. granati in trees subjected to regular watering and drought. Amylo-X LC proved effective in preventing P. palmivora damage and did not allow the synergistic effect of P. palmivora on C. granati to occur in trees under regular watering and drought. Drought further reduced P. palmivora lesions in plants pretreated with Amylo-X LC compared to those under regular watering. The impact of abiotic stress in pomegranate during C. granati and P. palmivora infections and the efficacy of B. amyloliquefaciens as a potential agent against pomegranate dieback were discussed. We conclude that further efforts to evaluate the efficacy of biological control agents on crops exposed to different environmental scenarios are needed.