Diversity And Pathogenicity Of Cryphonectriaceae Pathogens On Eucalyptus And Adjacent Mrytale Trees In Southern China

Plantation-grown Eucalyptus(Myrtaceae)and other urban planting trees residing in the Myrtales have been widely planted in southern China.However,relatively little is known regarding the fungal pathogens that affect them.These fungal pathogens include fungi of Cryphonectriaceae that are well-known to cause stem and branch canker disease on Myrtales trees.Previous research has shown that some species of Cryphonectriaceae have undergone host jumps from native Myrtales to infect non-native Eucalyptus.In this dissertation,the species diversity,host range and pathogenicity of Cryphonectriaceae associated with Eucalyptus and adjacent plants of Myrtales in southern China were studied.In chapter one,the species diversity of Cryphonectriaceae worldwide and the diversity of Myrtaceae tree species in China were summarized.The damage caused by Cryphonectriaceae species to various tree species of Myrtaceae in China and the potential for management of the risks of such diseases were also introduced.Our research team conducted a systematic disease surveys on Eucalyptus and adjacent Myrtales trees in Guang Dong,Guang Xi and Hai Nan Provinces during 2013 and 2016.The fruiting structures with typical characteristics of the Cryphonectriaceae were observed on the surfaces of cankers on stems and branches of Myrtales trees.Isolates of Cryphonectriaceae were obtained and identified.To understand the pathogenicities of these identified species,representative isolates of all fungal species were inoculated on different species of Myrtales.In chapter two,stem canker and cracked bark were observed on eight-year-old Eucalyptus grandis hybrid trees in a plantation in southern China.Fruiting structures typical of Cryphonectriaceae fungi were observed on the surface of the diseased tissues.Twenty-seven isolates of Cryphonectriaceae were identified based on DNA sequence analyses and morphological characteristics,and their pathogenicity was tested on three Eucalyptus genotypes.These fungal isolates were identified as Celopprthe syzygii,Cel.cerciana sp.nov.,and a potential hybrid species between Cel.syzygii and Cel.eucalypti.The inoculation results showed that these fungi isolated are pathogenic to all three tested E.grandis hybrid genotypes.Significant Significant differences in tolerance were observed between the tested Eucalyptus genotypes,genotype CEPT 46 is most tolerant,followed by CEPT 45,genotype CEPT 53 is relative susceptible.In chapter three,a total of 164 Cryphonectriaceae isolates were isolated from Eucalyptus,Melastoma(Melastomataceae),Psidium(Myrtaceae),Syzygium(Myrtaceae)and Terminalia(Combretaceae)in Myrtales.The 164 isolates were identified based on comparisons of DNA sequences and morphological characteristics.The pathogenicities of these identified species on Myrtales trees were tested.The results showed that eight species reside in four genera(including three novel species and one novel genus)of Cryphonectriaceae were identified and described.These fungal species include Cel.cerciana,Cel.eucalypti,Cel.guangdongensis,Cel.syzygii,Chr.deuterocubensis,a new genus and two new species,as well as one new species of Aurifilum,the new taxa hereby designated as Parvosmorbus gen.nov.,Parvosmorbus eucalypti sp.nov.,Par.guangdongensis sp.nov.,and Aurifilum terminali sp.nov..Of the eight species of Cryphonectriaceae identified in this study,Chr.deuterocubensis is the dominant species,followed by Cel.syzygii.Chrysoporthe deuterocubensis and Cel.syzygii were isolated from trees/shurbs of five and four sampled genera of Myrtales in this study,respectively.Based on the DNA sequences,genotypes of each isolate were determined in current study.The results indicated that the genotype diversities of Chr.deuterocubensis and Cel.syzygii are much higher than the other six Cryphonectriaceae species.Pathogenicity tests show that eight species reside in four genera of Cryphonectriaceae are pathogenic to two Eucalyptus genotypes,M.sanguineum branches,P.guajava and S.jambos seedlings.The M.sanguineum branches and P.guajava seedlings were killed by some inoculated isolates in a relatively short period.The overall data showed that Chr.deuterocubensis was the most aggressive,followed by Par.eucalypti.Significant differences in tolerance were observed between the two tested Eucalyptus genotypes,genotype CEPT 46 was more tolerant than CEPT 53,suggesting that disease-tolerant genotypes can be selected for disease management for Eucalyptus industry.