Objective To identify the pathogen causing tip blight on Aegiceras corniculatum in Zhanjiang City, Guangdong Province, China. The study involves elucidating the biological and molecular characteristics of the pathogen and screening for antagonistic bacteria, aiming to provide a basis for disease prevention and control.

Methods Isolation and purification of the pathogen were carried out using infected tissue samples and single spores. The isolated fungal strains were identified through morphological observations and phylogenetic analysis of concatenated gene sequences, including ITS, TEF-1α and TUB2. Biological characteristics such as growth rate, colony diameter, and growth morphology in different environmental conditions were assessed. Pathogenicity was confirmed by artificial inoculation on detached leaves of A. corniculatum. Antagonistic bacteria were screened using dual culture assays to identify potential candidates for controlling leaf tip blight.

Results  The isolated fungi displayed rapid growth on PDA medium at 28 °C, fully covering the Petri dish within 3 days. The aerial mycelium initially appeared white amd later turned gray, while the underside transitioned from white to a black center. Microscopic observation revealed septate hyphae forming thick-walled, spore chain-like structures. The conidia were oval to spindle-shaped, thin-walled, semi-transparent, and measured (15.19～19.66) × (4.59～6.07) μm (n=100). Morphological characteristics and phylogenetic analysis identified the strain as N. ribis. Artificial inoculation with the isolate caused symptoms identical to those observed in naturally infected leaves. The optimal growth temperature for the N. ribis strain THJK1A3 was 28 °C, with a narrow growth range; hyphal growth was significantly inhibited below 20 °C or above 30 °C. The optimal pH condition was determined to be 4. Finally, Bacillus amyloliquefaciens 68 demonstrated a 68.71 ± 2.56% inhibition of the hyphal growth of strain THJK1A3, suggesting its potential as a promising biocontrol agent for practical application.

Conclusion The causative agent of tip blight in A. corniculatum in Zhanjiang City, Guangdong Province, China, was identified as N. ribis strain THJK1A3. Additionally, B. amyloliquefaciens 68 demonstrated strong antagonistic activity against THJK1A3, making it a promising candidate for the biological control of this disease.