Preliminary Study On Phoma Leaf Spot Of Kiwifruit And Detection Of Kiwifruit Viruses

Kiwifruit（Actinidia chinensis Planch）is a special fruit tree planted in a large area in Fengxin County,Jiangxi province.In recent years,two new diseases of leaf spot and virus disease occurred on kiwifruit（cv.Jinyan）in the County.In order to ascertain the pathogenic species and carry out effective prevention and control,isolation,identification,biological characteristics and fungicide screening about the pathogen of leaf spot disease of kiwifruit were carried out,and the viruses in kiwifruit were detected.The results were as follows:48 diseased leaf samples were randomly collected from the kiwifruit（cv.Jinyan）orchard in Fengxin County.46 fungal strains with similar colony morphology were obtained by routine tissue isolation method.Pathogenicity of these strains were confirmed by artificial inoculation.The representative strain YB-1 was selected for morphological and molecular biological identification.The results showed that its culture characteristics,pycnidia and conidia morphology were consistent with previous descriptions of Phoma in the literature.The r DNA-ITS and GAPDH sequences had the highest homology of 100%and 99%with the corresponding sequences of Phoma bellidis in Genbank,respectively.The phylogenetic tree constructed with the assembling sequence of r DNA-ITS and GAPDH also grouped the tested strains and P.bellidis in the same branch.Based on the results,the pathogen of leaf spot on kiwifruit in Fengxi County was identified as P.bellidis.Biological characteristics of P.bellidis were tested.The most suitable temperature was25℃.PDA is the optimal medium.p H 7 or partial acid was beneficial to the mycelial growth of the P.bellidis.The best nitrogen and carbon sources were beef and glucose extract,respectively.In the photoperiod of 24 h light,the growth rate of the fungus was the fastest.The indoor toxicity of 9 fungicides to P.bellidis was determined by the mycelial growth rate method.The results showed that the different fungicides had different toxicities.EC₅₀values of 9 fungicides azole ether fluoroamide（42.4%）,oxanone manganese zinc（68.75%）,tebuconazole（430 g/L）,zole ether-daisenlian（60%）,tebuconazole oxime（75%）,iprodione（500 g/L）,chlorothalonil（75%）,prochloraz（450 g/L）,and difenoconazole（10%）were0.537μg/m L,1.399μg/m L,1.809μg/m L,2.689μg/m L,3.018μg/m L,3.111μg/m L,3.119μg/m L,5.510μg/m L,6.135μg/m L,respectively.It is clear that 42.4%azole ether fluoroamide had the strongest toxicity and 10%difenoconazole had the weakest toxicity.In order to determine the pathogen species of virus disease of kiwifruit（cv.Jinyan）in Fengxin County,a total of 40 samples of suspected virus disease leaves were randomly collected from 3 large-scale orchards.Total RNA were extracted and two common viruses of Actinidia virus A（Ac VA）and Actinidia virus B（Ac VB）were detected.Results revealed both of the two viruses were 100%present in all of the 40 smaples.After that,10 samples were selected from the above samples for detection of 13 other rare or newly reported viruses.Results showed that Actinidia chlorotic ringspots associated virus（Ac CRa V）and Citrus leaf blotch virus（CLBV）were detected,and the infection frequencies of Ac CRa V and CLBV were 100%and 40%,respectively.It is concluded that four virus species of Ac VA,Ac VB,Ac CRa V and CLBV can infect kiwifruit（cv.Jinyan）in Fengxi County,and the complex infection of the virus was very common.