Study On The Tripterygium Wilfordii Angular Leaf Spot

In recent years, people develop the medicinal value of the Tripterygium wilfordii increasingly. The vegetative cycle of Tripterygium wilfordii's root is very long and its leaves which can be used must live on the above 6-year old plants, therefore, the wild Tripterygium wilfordii are not enough to fulfill human's demand. In order to satisfy the human's demand, the local people have planted a large area of Tripterygium wilfordii pure stands in Taining country. With the appearance of the large-area planted forest, the diseases (such as powdery mildew, anthracnose, and angular leaf spot) are rampant, too. The angular leaf spot is so serious that the leaves' effective component is reduced greatly. Moreover, a lot of leaves are defoliated ahead of time, which causes a big economic loss for the local people. Simultaneously, because of our lack of the knowledge of the occurrence characteristics and development of Tripterygium wilfordii angular leaf spot in our province, the prevention is restricted. Therefore, we have made the systematic study on the identification and biological characteristics of the disease, the rule of the occurrence and development, the space distribution style of diseased plant, the chemical control of the disease and so on. The result is as follows:1. Symptom of the Tripterygium wilfordii angular leaf spotThe Tripterygium wilfordii angular leaf spot mainly did harms to Tripterygium wilfordii leaves. In the initial period, the leaves appeared some brown dots firstly. Then, the dots expanded to be triangular, polygonal, irregular spots with brown to black color and their diameters were 1 - 5mm. Then, some spots dissolved into a big irregular spot. With the spots' expansion, some leaves curled, withered and fell off ahead of time. Some seedlings withered to death. From the obverse surface of the leaf, spot's color gradually deepened from brown to black towards the outside. The periphery of the spot was light yellow-green, which was obviously lighter than the spot. But on the other surface, spot's color was light brown, which was obviously lighter than the obverse surface. Many black granules which were stroma could be seen on the obverse sides of spots in the end, rarely on the other surface.2. Identification and biological characteristics of the pathogenThe pathogen of the Tripterygium wilfordii angular leaf spot was proved to be Pseudocercospora elaeodendri (Agarwal&Hasija) Deigghton. The hypha growed well on PDA. The optimum temperature was 25℃and the most suitable pH was 5-6. To the carbon and nitrogen nutrition, the monosaccharide was the most advantageous to the hypha's growth in the carbon nutrition, and the peptone was the most advantageous to the hypha's growth in the nitrogen nutrition. The hypha used the nitrogen nutrition more strongly than the carbon nutrition. Conidia germinated fast in the appropriate temperature. They began to germinate after 2 hours, and the germination rate could reach 98.6% after 4 hours. The Conidia could germinate some buds from the two ends' cells, two ends and intermediate cells. The optimum temperature for Conidia germination was 30℃. The optimum pH was 6. Conidia could reach a response high germination rate if the moisture was more than 95 percent. The Conidia responded insensitively to light and its lethal condition is 50℃at 10 min.3. The rule of the occurrence and development of the Tripterygium wilfordii angular leaf spotThe Tripterygium wilfordii angular leaf spot was a kind of disease under the condition of high temperature and moisture. The pathogen survived in winter on the defoliation and invalid body in the form of hyphae. The pathogen invaded the plants from the natural orifices at the first ten days of May and the symptom appeared at the middle ten days of May. The disease developed from the leaves near the earth to the upside. The conidia were mainly diffused by rain and wind, and stoped developing in November. The fastigium was from July to August. The environment and the Tripterygium wilfordii's, age had a remarkable impact on the disease's occurrence and development. For example, the Tripterygium wilfordii angular leaf spot was more serious in the North Slope, in the middle of the stands and under the canopy. The 1-year seedlings' disease was most serious. The forest stand also had a strong impact on the disease development. Especially, and the disease of the mixed forest was less serious.4. Spatial distribution of diseased plantsThe result of congregation indexed and analysis of Iwao's regression and Taylor's exponential law model indicated identically that the spatial distributing type of the diseased plants of Tripterygium wilfordii angular leaf spot was the uniform distribution.5. The chemical control of the diseaseIn the measuring of house toxicity, the results of the study on the virulence bioassay by restraining conidia germination with toxic medium indicated that, eight kinds of fungicides except cabendazim, thiophanate-methyl and Prochloraz were efficient to restrain the conidia germination. "Guo fu da M-50" had the best restraining effects, all of which were above 90 percent, followed by "sheng gao". Prochloraz was the worst. Through the regression equation of Toxicity and results of EC₅₀, we could find that,"sheng gao", "guo fu da M-50" and Sandofan M8 were efficient to the conidia in sensitivity and virulence. In the study of fungicides' impact on the hypha growth, eight kinds of fungicides except Prochloraz had strongly inhibitory effects. Particularly, the inhibitory rates of shenggao, "guo fu da M-50" and Sandofan M8 were very high. According to the sensitivity, the results were as follows:"sheng gao"> "guo fu da M-50"> Prochloraz>thiophanate-methyl> carbendazim> Dithane Z-80> Sandofan M8> Mancozeb; According to the toxicity, the result was as follows: Sandofan M8 > Mancozeb > "sheng gao"> Dithane Z-80 > "guo fu da M-50"> carbendazim> thiophanate-methyl> Prochloraz. "Sheng gao" and "guo fu da M-50" had better results in the sensitivity and virulence on the hypha growth.In the field test of disease controlling, four kinds of fungicides were efficient. "Sheng gao"had the best effects on the 7th day after the third spraying. With the fungicides' dilutions of 500 times, 800 times and 1000 times, the inhibitory rates of "sheng gao" were 72.36%, 67.90% and 63.94% respectively. On the 14th and 21st day, "sheng gao" remained the best one, followed by Sandofan M8, and Mancozed was the worst one. The results showed that, there was a remarkable diversity between different fungicides, fungicides' dilutions and control periods. "Sheng gao" had the best effects in fungicides, and 500 times had the best effects in different fungicides' dilutions.6. The loss assessment and the controlling index of the diseaseThis study focused on the characteristics of Tripterygium wilfordii angular leaf spot, used the linear relationship between the disease index and the loss, and adopted the artificial methods to establish the approximate loss of key condition of regression forecasting model. On the basis of the model, we built the loss rate which the economy allowed, the mathematical model of disease index indicators and the control index. We educed the loss rate which allowed by current economic level (Y_EIL) is 15.48%, and identifiedthe specific targets X_ET=[(W×F/P×D×Q+13.586)/0.993-T×R]×Q for prevention and treatment,according to the actual situation guiding production practice.