Study On The Biological Characteristics Of Pseudocercospra Elaeodendri In Tripterygium Wilfordii

Angular leaf spot disease seriously reduces the production of Tripterygium wilfordii, especially in the humid and warm zone. The plant infected by the pathogen appears to be premature defoliation,it causes the weakness or dead of plant, which leads to yield loss.In this study, the author isolated and purified the fungus. According to the morphological characteristics of fungus and Koch's postulates, it was similar to the description of Liu XJ and Guo YL. Therefore, the isolated fungus was identified as Pseudocercospora elaeodendri, Futher, the DNA sequence data from the internal transcribed sequence (ITS) region was amplified and analysed in the Gene Database of National Center for Biotechnology Information (NCBI). The results suggested that the ITS sequence of the fungus was the same as Pseudocercospora sp. of lilac leaf spot, and highly similar to other Pseudocercospora species. Phylogenetic data of 20 stains obtained here indicat the test stain was clustered with P. sp., but different from those other Pseudocercospora species. The results suggested the obtained should be P. elaeodendri.Study on the biological characteristic of P. elaeodendri, the results showed that the same growth rate of hyphae was observed per day, and ageing of hyphae presented after 20 days. The best conditions for hyphae growing were carrot medium with pH value at 4.5~9, under the cultured temperature at 27℃~29℃. Light or dark condition has no effect on hyphae growth. In fifteen artifical cultures, Malt medium is the optimal medium for spore production and the best sporulation pH value is 6.Temperatures maintains at 31℃and dark condition are best for spore production. Conidia start to germinate after 3h incubation and the average length of germ tubes is 6.6um. Germination rate exceeds 90% after 7 h incubation and the average length of germ tubes is 32.5um. Conidia can germinate from any cell, but mostly from the end cells (about 82%). They have 1~7 germ tubes and constricted when germinate. The ideal pH value for spore germination is 3, under the best spore temperature at 29℃~31℃. Dark condition, high humidity and leaf juice also contributed to spore germination. The microscope observation of leaf and fungus suggests that the adaxial surface has no stomata whereas stomatal density is 214.55 No.·mm-2 on the abaxial surface. New conidia could be detected within 2 d of incubation. After 24 h inoculation, germ tubes of conidia emerged to the stoma directly, according to the result of scanning electron microscope (SEM). The effects of 8 fungicides were examined in vitro on germination of P.elaeodendri. Inhibitor of germination rate of <10% were found for pyrimethanil(70 mg·L-1), iprodione(100 mg·L-1), thiophanate-metlyl(100 mg·L-1)and tradimefon(100mg·L-1)after 7 h incubation. Significant effect of fungicides was75% mass fraction chlorothalonil WP with EC50=0.49 mg·L-1, EC= 0.78 mg·L-1, 25% mass fraction procymidone thiram WP or 80% mass fraction mancozeb WP came next. Both 75% mass fraction chlorothalonil WP and 25% mass fraction procymidone thiram WP were tested on T.wilfordii infected by P.elaeodendri. 500 mg·L-1 procymidone thiram is better than chlorothalonil on therapeutic effect.