Spore Germination, Infection Of Coleosporium Phellodendri And Disease Dynamic In Field

The phellodendron, belonging to family Rutaceae and genus Phellodendron Rupr. includes two species which are P. chinense Schneid. and P. amurense Rupr. The bark of phellodendron is used as a medicine for more than 2000 years. It is one of the typical Chinese medicinal plants in Sichuan province. The thick and color depth bark of phellodendron is used to extract berberine hydrochloride, because the bark is high content of berberine hydrochloride. The phellodendron is widely distributed and can improve soil and water conservation benefits, so it is one of the excellent species in soil and water conservation in mountain area.During the growth process of phellodendron, the leaf rust, which is the chief serious disease harming Phellodendron chinense, has become a major obstacle and constraints in phellodendron production. The disease is caused by Coleosporium phellodendri Kom. Therefore, the research on spore germination, infection of C. phellodendri and disease dynamic in field, is very important for enriching the research on C.phellodendri,and also very important for forecasting and controlling this disease. This paper has firstly made research on these aspects of C. phellodendri and disease dynamic in field and so on. The main results are as follows:1 On germination of uredospore, teliospore and basidiospore of pathogenThe development of uredospore was observed by tissue slice. The result showed that a small wedge-shaped cell known as an intercalary cell was formed at the bottom of the immaturate uredospores during the development of urediospore, The intercalary cells would disappear when the uredospores were mature.When the uredospores germinated on the 1.5% water agar, most of the uredospores generated two or three germ tubes and a few generated one germ tubes, while sparse uredospores generated four germ tubes. The germ tubes elongated and formed hyphae. After that the top of hyphae inflated and generated appressoria.The research on uredospore germination in different substance showed that the uredospores could not germinate in the sterile water, but could germinate well on the 15% water agar. The rise of temperature in the range of 15-30℃promoted the germination of uredospores, but inhibited the elongation of germ tubes obviously. The pH value range for uredospore germination was pH6-7.5, with the optimum range in pH6-6.5. The light inhibited the germination of uredospores obviously.The telia were generated under the epidermis and formed cushion-like apophysis after maturity. The teliospores were arranged in parallel as well as a palisade in the telia, with sessile, unicellular, cylindrical and golden brown appearance. There was a transparent and sheath-like structure covering the teliospores. The thickness of this structure was about 7-14μm. The top of immature teliospores was ebetate and had two nuclei. With the elongation of teliospores, the two nuclei merged into one nucleus, which represented the maturity of teliospores. The top of the mature teliospores was obtuse or truncate. The size of mature teliospore was about 42-58×13-24μm.After the teliospores were mature, they continued to stretch. A septum was formed in the middle of each teliospore to separate the teliospore into two parts, the upper-part was golden yellow with protoplast which would developed into a basidium and then to be basidiospores。while the bottom was transparent like a stipe. The teliospores could germinate in the range of 5-25℃, with the optimum at 20℃.The germination of basidiospore was observed on 1.5% water agar. The result showed that a basidiospore was oval or reniform with an apiculate apophysis at the bottom of the spore. The size of basidiospore was about 20-25×12-15μm.The basidiospores could germinate in the range of 5-25℃and formed only one germ tube. And then a secondary spore that looked like the basidiospores was formed. The secondary spores went on to germinate and generate a germ tube, while only a few formed sporidia again.2 The infection process and infection condition of pathogenSix hours after incoluation, the uredospore germinated on the leaf surface. The uredospores on lower epidermis germinated and formed an appressorium. The appressorium germinated and formed an invading hypha. The invading hypha penetrated into the leaf through stomata. The uredospores on the upper epidermis could not form an appressorium generally. It often formed a hypha penetrating into epidermis directly.The effect of temperature on infection was studied in the growth cabinet. The results showed that uredospores could infect the leaves of P. chinense and caused disease in the range of 15-28℃, with the optimum at 25℃. If the moisture preserving time was more than 12h, the leaf rust could occur.The longer moisture preserving time was, the more serious the disease was. Similarly the older the foliar age was, the more serious the disease was. When inoculating the upper epidermis and lower epidermis of leaf surface with uredospores respectively, both of them could cause disease. The incubation period was 12d and 8d respectively. The telia were generated in the temperature range of 15-25℃. With temperature falling, the formation time of telia was shortened and the quantity of telia increased.3 The disease dynamic of leaf rust and the hyperparasite of Coleosporium phellodendri in fieldThe result of two years local and general survey of the leaf rust in field showed the leaf rust caused by C. phellodendri occurred initially at the end of May or at the beginning of June. From the middle of June to the middle of August, the disease developed and spread quickly in field. After that the disease index continued to increase, but the tendency was gradually constant, the disease became less serious, along with the dropping of leaves, it would stop. The teliospores appeared after the middle and late of July and generated large amount in the middle and late of August.The hyperparasitism occured approximately 10-15d after the occurrence of leaf rust. Along with the increase of leaf rust, the severity of hyperparasitism increased. Although the dynamics curve of hyperparasitism was similar to that of the leaf rust, the progress of the hyperparasitism fell behind that of the leaf rust obviously.