Study On The Etiology Of Apple Ring Rot

Apple ring rot is one of the most important apple diseases in china.The pathogens can infect fruit,branches and trunks,results in rot on fruit,especially during fruit storage,and extensive cankers or warts on branches and trunks,eventually resulting in tree death with tree vigour weakening.The species of the pathogens were confused and the source of infection was vague,thereby affecting the disease control and prevention research.Most of samples were collected from apple from 28 locations in four provinces in China.To provide context,samples from other trees around apple orchards were also collected.389 samples were collected and the 286 pure strains were obtained.By studying on the etiology of apple ring rot,the main results were as follows:1.rDNA-ITS phylogenetic analysis showed that,the pathogens of apple ring rot in China consists of three Botryosphaeria species:Botryosphaeria dothidea complex-species,Botryosphaeria parva and Botryosphaeria stevensii,97%isolates polymerize with B.dothidea complex-species,and another each species contained 1.5%isolates,so the B.dothidea complex-species is the predominance group.2.The multilocus sequences phylogenetic analysis showed that B.dothidea complex-species was divided into two groups with high approval rate.Further study show there were obvious distinctions in the morphology,biology and pathogenic aspects between the two groups,so we think the two groups were stand for different species.One group was B.dothidea sensu strict,other group was identified as a new species and named Botryosphaeria pomicola C.S.Wang&G.Y.Sun.The result of pathogenic study showed that the symptoms caused by B.dothidea and B.pomicola were obviously different.Symptoms caused by B.pomicola is heavy,diameters of warts were 2-3 mm and height were 1-2 mm;Symptoms caused by B.dothidea is lighter,diameters of warts were less than 2 mm and height were about 1mm.So we suggested that the diseases caused by B.dothidea and B.pomicola on trunks and branches were respectively named Botryosphaeria canker and Botryosphaeria wart.3.The host range of B.dothidea was wide.Strains of B.dothidea were got from the trees near the orchards,including pear,peach,pomegranate,poplar,jujube and willow.These strains could infect apple and caused the typical symptoms of apple ring rot when they were inoculated on trunks of apple seedlings.Strains of B.pomicola from pears were also noculated on trunks of apple seedlings and caused disease.These results showed that strains from others hosts were the infection sources of apple ring rot.4.The rapid identification methods for B.dothidea and B.pomicola.It found that there is an intron in 18S rDNA of B.pomicola strains by part sequences of the small subunit ribosomal DNA(SSU)amplified.The B.dothidea strains did not have the intron in the same locus.It would be easy to distinguish between B.pomicola and B.dothidea by amplifying the sequence of the intron.Strains were incubated at 25? on PDA for a week,colony diameter of B.dothidea was more than 60 mm,and colony diameter of B.pomicola was about 20 mm,it was a rapid method to distinguish between the two species.5.The multilocus sequences phylogenetic analysis showed that the pathogens of apple white rot were belong to two branches,so the pathogen species of apple ring rot and apple white rot were same.6.B.dothidea was world-wide.By the multilocus sequences phylogenetic analysis and sequences blast in the Genbank,B.pomicola was found in Japan?Korean?American?Australian?New Zealand and so on.It showed that B.pomicola was also word-wide.