Study on the biological characteristics of Septoria apocyni affecting Apocynum venetum

Leaf and stem spots caused by Septoria apocyni are indicative of fungal diseases that significantly affect the production and quality of Apocynum venetum. This mainly damages the leaves and stalks of A. venetum. On the leaves, ring-shaped spots are formed in the early stages, and the stems are damaged later. The lesions are connected with severe infections, and the plant exhibits burnt signs and dies later. The present study systematically investigated the biological characteristics of two strains, Gansu (GS) and Xinjiang (XJ). This study clarified the effects of different culture media, pH values, temperatures, and light, on colony growth and screened the best culture conditions for S. apocyni on A. venetum. The results showed that GS strains grew best on PDA, whereas XJ grew best on 10% A. venetum juice mixed with PDA. The fungi did not produce spores on the seven culture media provided for testing. The colony could grow in the range of 10～30 ℃, and the optimum temperature was 25 ℃; the fungi could also grow in the pH range of 4～10, with an optimum pH of 5～5.5. Both GS and XJ grew best under light and dark conditions. The results provide a basis for further study of this pathogen and disease.