Objective  The present paper aimed to identify the pathogen causing leaf spot on Pittosporum tobira, to study the biological characteristics of the pathogen, and screen out effective fungicides to control this disease.

  Method  The pathogen was isolated from the leaves with typical symptoms by tissue separation method and verified by pathogenic test. The morphological and molecular biology methods were used to identify species of the pathogen. The mycelium growth in plate was used to investigate the biological characteristics and fungicides toxicity of the pathogen.

  Result  The HT10 strain was isolated from the disease leaves and inoculated onto healthy P. tobira. After inoculation, the center of the disease spot was grayish brown, the edge was brown, and the periphery was yellow halo, which was consistent with the field’s symptoms. On PDA media, the fungal colonies displayed brown and black. Conidia were inverted rod, ovoid or nearly elliptic, with transverse and longitudinal septa. The phylogenetic analysis used multiple genes of ITS, GAPDH and RPB2 clustered the isolate with Alternaria longipes clade. The optimum growth condition on PDA were full light, 28 ℃ temperature and, 6.0 pH. The optimal carbon source or nitrogen source is sucrose or glycine, respectively. The lethal temperature is 41 ℃/15 min. Laboratory toxicity test showed that the 25% SC of Imazalil·Fludioxonil has the best inhibitory effect to pathogenic fungus with EC₅₀ of 0.799 μg·mL⁻¹ and the 400 g·L⁻¹ SC of Captan·Tebuconazole has the worst inhibitory effect with EC₅₀ of 370.457 μg·mL⁻¹.

  Conclusion  The pathogen causing the leaf spot disease on P. tobira is A. longipes, which is the first report of leaf spot disease on P. tobira caused by A.longipes. 25% SC Imazalil·Fludioxonil has a strong inhibitory effect on the growth of A. longipes.