Effects of Torreya grandis Root Rot on Seedling Growth and Screening of Its Chemical Control Agents

[Objectives]This study was conducted to prevent the occurrence of root rot disease in Torreya grandis and improve the yield and quality of T.grandis.[Methods]One-year-old and two-year-old seedlings of Torreya grandis‘Xifei’and‘Cufei’were inoculated with the root rot pathogen Fusarium fujikuroi,and the changes in photosynthesis,chlorophyll content,malondialdehyde,and defense enzyme system(superoxide dismutase,peroxidase,and catalase)activity in leaves of T.grandis seedlings were investigated using water as a control.Meanwhile,the control effects of 80%carbendazim wettable powder,64%metalaxyl·mancozeb wettable powder,430 g/L tebuconazole suspension and 30%difenoconazole·cyproconazole EC on root rot in T.grandis were investigated.[Results]After inoculation with the pathogen F.fujikuroi,the net photosynthetic rates and transpiration rates in leaves of T.grandis‘Xifei’and‘Cufei’decreased,and the contents of chlorophyll decreased,while the contents of malondialdehyde increased,and the contents of superoxide dismutase and catalase increased with time.However,peroxidase showed a high activity in T.grandis‘Cufei’only,but a trend of"increasing-decreasing-increasing"in T.grandis‘Xifei’.Among the four chemical control agents,64%metalaxyl·mancozeb wettable powder had the best control effect on root rot of T.grandis caused by the pathogenic fungus F.fujikuroi.[Conclusions]The net photosynthetic rate,transpiration rate,chlorophyll content,malondialdehyde content,superoxide dismutase activity and catalase activity could all be used as screening indicators for T.grandis varieties resistant to root rot.Meanwhile,64%metalaxyl·mancozeb wettable powder could be used as a control agent for root rot on T.grandis.

Natural infectious behavior of the urediniospores of Melampsora larici-populina on poplar leaves

The uredinial stage in the life cycle of Melampsora larici-populina on poplar leaves is the most important pathogenic phase. We captured partial phases of uredinial infection in the wild, aiming to reconstruct the process of uredinial ontogeny by using scanning and transmission electron microscope. At the initial infection stage, germ tubes germinated from the echinulate urediniospores. Germ tubes were frequently seen to merge with the leaf surface and cuticle breakage was observed, indicating direct hyphal penetration. Stomata penetration occurred commonly, sometimes with more than one germ tube penetrating the same stoma. Melampsora larici-populina did not form appressoria in the infection process,implying that infectious behavior of this pathogen may differ from the other rust pathogens. In general, germ tubes branched randomly, and no distinct evidence indicated that stoma could induce or orient germ tube branches. However, oriented germ tube growth has been occasionally observed in other studies. The urediniospores collapsed and finally wizened when they became nutrient stressed. At the last stage of infection, the uredinia erupted from the leaf epidermis and appeared as orange pustules on the leaf surface.