Species Diversity,Mating Strategy And Pathogenicity Of Calonectria Species From Diseased Leaves And Soils In The Eucalyptus Plantation In Southern China

Many Calonectria species are causal agents of diseases on several forestry,agricultural and horticultural crops.Leaf blight caused by Calonectria is a wordwide disease,which is particularly harmful to Eucalyptus plantations in Asia and South America.In this thesis,the species diversity,geographic distribution and host of Calonectria are summarized;the damage details of Calonectria pathogens to Eucalyptus are described;the inoculation methods and conidia induction methods for Calonectria species are documented;and the pathogenicity characteristics of Calonectria species on Eucalyptus are also summarized.In China,Calonectria leaf blight caused enormous economic losses to the Eucalyptus industry.Calonectria species are widely distributed in diseased leaves and soils under the Eucalyptus trees.However,the differences of species diversity,genetic structure,mating type and pathogenicity of Calonectria isolated from diseased leaves and soils under Eucalyptus plantations remain unknown.In this study,a total of 368 Calonectria isolates were isolated from diseased leaves and soils under the ten Eucalyptus urophylla hybrid genotypes in Guang Xi Province.And 245 representative isolates were selected based on the sampling substrates and Eucalyptus genotypes and identified by DNA sequence analyses based on the translation elongation factor 1-alpha(tef1),β-tubulin(tub2),calmodulin(cmd A)and histone H3(his3)gene regions,as well as a combination of morphological characteristics.These isolates were identified as Calonectria hongkongensis(50.2%),Ca.pseudoreteaudii(47.4%),Ca.aconidialis(1.6%),Ca.reteaudii(0.4%)and Ca.auriculiformis(0.4%).This is the first report of Ca.reteaudii and Ca.auriculiformis occurrence in China.MAT1-1-1 and MAT1-2-1 gene were amplified to confirm mating type(MAT)of each Calonectria species.The results showed that Ca.pseudoreteaudii is heterothallic,Ca.reteaudii and Ca.auriculiformis are likely to be heterothallic and Ca.hongkongensis and Ca.aconidialis are homothallic.Calonectria pseudoreteaudii was isolated from both diseased leaves and soils under Eucalyptus trees;the other four species were only obtained from soils under Eucalyptus trees.The results of genotype analyses by sequences of tef1,tub2,cmd A,his3,MAT1-1-1 and MAT1-2-1 gene regions showed that the genetic diversity of Ca.pseudoreteaudii isolates from diseased leaves is higher than isolates from soils.All five Calonectria species were selected to inoculate on two Eucalyptus genotypes CEPT1876 and CEPT1877 by the mycelia plugs and conidia suspensions.The results showed that all five Calonectria species were pathogenic to the two Eucalyptus genotypes.This study confirmed that Ca.pseudoreteaudii is causal agent of leaf blight on ten Eucalyptus genotypes in Guang Xi Province,and Ca.hongkongensis,Ca.auriculiformis,Ca.reteaudii and Ca.aconidialis are potential pathogens to Eucalyptus in China.The results indicated that pathogenicities of isolates of Ca.pseudoreteaudii obtained from diseased leaves are higher than these isolated from soils under Eucalyptus trees,while the differences are not significant.The tolerance of the two Eucalyptus genotypes differed,Eucalyptus genotype CEPT1876 is more tolerant than CEPT1877 to most tested Calonectria isolates.This study further confirmed that Ca.pseudoreteaudii is an important pathogen which causes Eucalyptus leaf blight in southern China,and expanded our understanding of the genetic diversity,morphological characteristics,host/substrate range,mating type and pathogenicity of Calonectria species in diseased leaves and soils in the same Eucalyptus plantation.