Potentiel antagoniste des rhizobactéries d’azadirachta Indica contre trois champignons phytopathogènes

Abstract

Fungal diseases represent major threat to global agricultural production, causing estimated yield losses of 10 to 23%. Despite the widespread use of chemical fungicides, biological control agents (BCAs) often lose effectiveness under prolonged drought episodes. This study aimed to isolate and evaluate the antagonistic potential of rhizobacteria associated with Azadirachta indica (neem) in the semi-arid region of Far North Cameroon. The rhizobacteria were isolated on nutrient agar and screened for antagonistic activity against Fusarium verticillioides, Macrophomina phaseolina, and Aspergillus flavus. The antagonistic isolates were subjected to direct and indirect confrontation assays to quantify their antagonistic potential. The most promising isolates were further assessed in planta against F. verticillioides. Agro-morphological, physiological, and biochemical parameters, as well as disease-related traits, were evaluated through direct measurements and spectrophotometry. 53 rhizobacterial isolates were obtained, of which 14 exhibited inhibitory action against the three phytopathogens studied. Isolates SZ1 and SZ12 displayed strong direct antagonistic effects, culminating at 95%, while in indirect confrontation, isolates SZ12 and SZ15 were most effective, with inhibition rates of 97.95% and 97.53%, respectively. Seed pretreatment with BCAs enhanced growth parameters by 66.7–90.66%, including shoot and root length as well as fresh and dry biomasses, compared to infected untreated controls (F. verticillioides alone). Isolate SZ1 was particularly effective, conferring 66.5% seed protection and significantly increasing chlorophyll (111.1%) and carotenoid (646.83%) contents. Moreover, SZ1 reduced PAL (32.39%), PPO (19.48%), and proline (1.8%) levels relative to infected untreated plants. Overall, these findings suggest that isolate SZ1, recovered from Azadirachta indica, represents a promising candidate for the development of effective biopesticides with enhanced resilience to environmental stresses associated with climate change.