The Effects Of Citrus Cuticular Waxes On The Developments Of Penicillium Digitatum And The Identification Of Plant Powdery Mildew Pathogens

Citrus is one of the most important economic fruits in south of China and one of the most important fruits in the global fruit industry.However,due to the fact that citrus is easy to be infected by a variety of fungal pathogens during postharvest transportation and storage,fungal diseases caused by penicillium sp.are the most serious among them.Nowadays,research on citrus and penicillium diseases mainly focuses on new or alternative methods of disease management and anti-fungal mechanisms of plants during pathogen infection.However,there is only scarce information available on the effects of citrus cuticular waxes on the developments of penicillium sp.,and more research is needed.Powdery mildew fungi are one of the most common fungal pathogens of angiosperms,which seriously damage the ornamental and economic value of plants.At present,there have been some reports on the identification of plant powdery mildew pathogens all over the world,while due to powdery mildews are plant specific pathogenic fungi,the species of powdery mildew on different plants may be different,more research and information is needed for the host-specific phytopathogens.To study plant fungal pathogens,this dissertation includes the research on impacts of mandarin fruit cuticular waxes on developments of the green mold pathogen,penicillium digitatum and on identification and classification of powdery mildew fungi.The projects intend to study penicillium digitatum and powdery mildews on Zinnia elegans,Aristolochia debilis,Poa pratensis,Lycium chinense,Koelreuteria paniculata,Bromus catharticus.The main results were as follows:1.The cuticular waxes of Citrus reticulata Blanco inhibited the colony expansion of Penicillium digitatum.It was found that in vivo,after 72 h of inoculation with penicillium digitatum,the area of fungal colony on the surface of dewaxed citrus fruit was 46 mm~2 and 53 mm~2,respectively,it’s significantly larger than that on the surface of intact citrus fruit was 19 mm~2,34 mm~2and 37 mm~2,respectively.After 96 h of inoculation,similar patterns were observed.In vitro,expansion of fungal colony on the wax-coated PDA was impaired comparing to it on PDA medium.2.After 6 h of inoculation,the germination ratio of conidia on the PDA agar was 12%,which was slightly lower than those on the PDA supplemented with chloroform or chloroform/citrus wax,the number of germinated spores on the wax membrane increased significantly to 23%.After 9 h and 12 h of inoculation,the numbers of germinated conidia on the PDA agar were the lowest（69%and 91%respectively）and the proportions of spore germination on the wax membrane were the highest（90%and 99%respectively）.On the PDA media,after 6 h of inoculation,the average length of conidial germ tube was 9.8μm,which was slightly higher than those formed by spores on the PDA supplemented with chloroform or chloroform/wax（9.0μm and 8.9μm respectively）.However,the average length of the germ tube produced by the conidia on the wax membrane increased notably to 12μm.After 9 h and 12 h of inoculation,the germ tube length of the conidia on the PDA and PDA supplemented with chloroform or chloroform/wax were similar（around 17μm and 33μm,respectively）,and the spores on the wax membrane formed the longest germ tube（22μm and 43μm,respectively）.This indicating the conidial germination and germ tube elongation was triggered by cuticular wax of citurs fruits.3.The pathogenic fungi of powdery mildew identified in this study caused severely plant diseases but differed in severity.The asexual and sexual morphes of powdery mildew on Koelreuteria paniculata were observed.Asexual morph of powdery mildews on other 5 plant species were monitored.The symptoms of powdery mildew were found on the adaxial surfaces of leaves of Poa pratensis and Bromus catharticus,while the symptoms of powdery mildew were observed on the adaxial and abaxial surfaces of the leaves of the other four species.4.Among the 6 species of plant powdery mildew pathogens identified in this study,the powdery mildew fungus of Aristolochia debilis were reported for the first time in the world,the powdery mildew fungus of Zinnia elegans,Poa pratensis were reported for the first time in China,Koelreuteria paniculata and Lycium chinensis were reported for the first time in Henan,China.（1）The powdery mildew of Zinnia elegans was Golovinomyces cichoracearum（Erysiphales,Erysiphaceae）,and its ITS sequence No.was MW029904 in Gen Bank.（2）The powdery mildew of Aristolochia debilis was Erysiphe sp.,and its ITS sequence No.was MN700999 in Gen Bank.（3）The powdery mildew of Poa pratensis was Blumeria graminis f.sp.poae（Erysiphales,Erysiphaceae）,and its ITS sequence No.was MT892956 in Gen Bank.（4）The powdery mildew of Koelreuteria paniculata was Sawadaea koelreuteriae,and its ITS sequence No.was MT008194 in Gen Bank.（5）The powdery mildew of Lycium chinensis Mill was Arthrocladiella mougeotii,and its ITS sequence No.was MT007282 in Gen Bank.（6）The powdery mildew of Bromus catharticus was Blumeria graminis f.sp.bromi,and its ITS sequence No.was MT892940 in Gen Bank.