The Preliminary Study Of Oidium Biological Characteristic, Infection Process And Its Host Resistance Responses

Powdery mildew is a detrimental disease of eagle tea(Litsea Coreana Levl. Var.Lanuginose) in the commercial growing area in Ya an, Sichuan Province. This diseaseinduces abnormal leaf shapes and adversely affects the eagle tea productivity.The studyrecorded and demonstrated the symptoms and signs of this disease in details,andsystrmatically studied the pathogenic fungus's biological characteristics,pathogen-hostinteractions,and host plant physiological and biochemical defense responses.According tothe morphological characteristics including the sizes of the conidiophore and condium,thepathogen was identified as oidium.Oidium can grow both in the acid or alkaline environment. The spore germination canhappened in pH ranges 3.0-12.0.,and with the optimum pH for sporulation at 10.0.Theoptimum temperature for sporulation ranged 15 to 25℃,and the optimum humidity is100％. Dark or indirect illuminations are advantageous to spore formation.The ultravioletlight(UVL) is devastating to oidium spore,and the longer the UVL illumination the less thegermination.This study showed that there were no spore germination after treated withUVL for 30 min.In the Study, resistance to powdery mildew caused by pathogenic fungus oidium of 5commercially important eagle tea cultivars in Sichuan procince were evaluated both in thefield and in the laboratory on artificially inoculated plants. Results were consistent for thetwo evaluation methods,and therefore,we concluded that artificially inoculation in thelaboratory is reliable and feasible,especially when a large amount of cultivars wereinvolved.Our evaluations found that,among five eagle tea cultivars,one cultivar was highlyresistant,two cultivars were susceptible,and the rest two cultivars were medium resistant.In the study, electronic scanning microscope and optical microscope were usd toobserve the host-pathogen histological interactions in different phases.The results showedthat at 4h after inoculation,the primary germ tubes were emerged from the germinatingspores.At8h after inoculation the appressorium germ tube formed appressorium.At12hafter inoculation appressorium formed appressorium lobe or second appressorium lobe andappressorium induce host cells formed halo.at 24h afer inoculation, appressoriumdeveloped further into haustoria. At 48h after inoculation, the primary hyphae grew fromthe apex of the appressorium over the surface of the host epidermal cells.At 72h afterinoculation,primary hyphae developed into secondary hyphae.The time course changes in the activity of photosynthesis, peroxidase(POD), catalase (CAT), polyphenolo xidase (PPO), phenylalanine ammonialyase (PAL)and the contain ofmalonaldehyde(PPO), solublesugar, sotuble protein,chlorophyll were studied systemically.The results showed that the acticities of photosynthetic rates,transpiration rates,PO,PPO,CAT activities, and soluble sugar contents were correlated with different eagle teacultivar resistances to powdery mildew.As comparison to,the acticity of PAL was relatedto susceptibility.This study also found that soluble protein extracted from the infectedleaves were significantly less than control(non-infected leaves),and the differences amongcultivars,however, were negligible.