Identification And Antifungal Activity Of XF, An Antagonistic Fungus Against Phytophthora Infestans

XF₁, XF₂, XF₃ are three strains of one fungal species XF isolated and purified by ourlab, which have strong inhibition effect to Phytophthora infestans. Test in vitro showedthat the inhibition zone width to P. infestans all surpassed 1.6 cm and did not change muchalong with time. Suppressive spectrum test indicated that the bioeontrol strain XF₁ showedno antagonistic effect against mycelium growth of Botrytis einerea, Alternaria solani,Alternaria brassicae, Verticillium dahliae, Rhizoctonia solani and Fusarium oxysporum.Based on morphological characterization, XF was indentified to be in the genus ofEpicoccum. Molecular biological methods were used to amplify and analyze the sequencesof ITS of XF. In the end the fungal XF was identified to be Epicoccum nigrum.Biological characteristics research showed that different growth media had greatinfluence to the growth of XF₁. The aerial hyphae on Rye agar were khaki and villiformwhite colony but with black spores on colony. On Czapek media no spores were formed,the aerial hyphae were white wadding. On PDA media the color of elliptic colonies werekhaki. While on PSA media the aerial hyphae were khaki and ellipticwith sectored colonyof sparse and light yellow color. In general, Rye agar was the best medium for XF₁vegetative growth and spore production. XF₁ can grow at temperature range of 5～35℃andpH range of 4～12, in which the optimal temperature was 28℃and pH was 7. Hyphaebecame crinkle on acidic medium, while grew well on neutral and alkaline medium. Incarbon source test, maltose and dextrose were best to support the growth of XF₁, whiletri-sodium citrate could suppress mycelium growth. Among the nitrogen sources tested,peptone, KNO₃, and NaNO₃ were the best. Spores of strain XF₁ can germinate attemperature 5～35℃. At the optimum 20℃, the percentage of germination could reached80ï¼…after 12h, and surpassed 90ï¼…after 24h. The optimal temperature for sporulation was18℃. The lethal temperature for the germination of spore was 43℃, 10 min.In order to find out the metabolism substance and bioactivity of XF₁, Rye broth wasused to isolate the components with inhibition effect against P. infestans. The waterextracts of supernatant and dry mycelia without polysaccharide had strong antagonisticeffect against P. infestans. The results showed that the effective concentration (EC₅₀) of thewater extracts of supernatant without palosaccharide (WQT) against zoospore release andmycelium growth were 2.72 mg/mL and 4.01 mg/mL, respectively; while the EC₅₀ of drymycelia without polysaccharide (NQT) against zoospore release was 2.81 mg/mL. Becausethe water extracts were obtained at 100℃, so the inhibitory effective components of XF₁ were thermostable.