| Apple white rot is one of the important diseases (apple canker, apple white rot and apple early defoliation) in apple production. It can infect limbs and fruits, cause limb epidermis crevices, nodulation and fruit decay, and cause fruit rot during storage, so it takes serious loss to apple production both in field and in storage. Pathogen of apple white rot was short of systematic research and the name of pathogen was used confusedly, so it is urgently to carried out research on systematic identification, species constitution and pathogen diversity in china.Samples were collected from apple producing regions including Weinan, Baishui, Luochuan, Pucheng, Hancheng, Qianxian, Wugong, Bingxian, Xunyi, Chunhua, Jingyang, Fufeng, Qishan, Dali, Fengxiang, Heyang, Yangling, jiangzhang, Qianyang etc. 347 samples were collected and 212 isolates were obtained from samples. Pathogens were identified based on morphological characteristics and rDNA-ITS phylogenetic analysis. Pathogen diversity analysis was carried out by phylogenetic analysis and SSR analysis. The results were as follows.(1) rDNA-ITS phylogenetic analysis showed that, pathogen of apple white rot in Shaanxi province consists of three Botryosphaeria species: B. dothidea, B. obtusa and B. malicola, 95.2% isolates polymerize with B. dothidea species, and another each species contained 2.4% isolates, so the species B. dothidea is the predominance group in Shaanxi apple production areas.(2) rDNA-ITS phylogenetic analysis showed that the pathogen of several related diseases, including poplar canker, zythia versoniana, gummosis of peach, pear ring rot, all belong to B. dothidea, which is same to apple white rot. It was presumed that the pathogen could be the infection sources to apple white rot in fields.(3) rDNA-ITS phylogenetic analysis showed that isolates of B. dothidea were catalogued into 2 groups. SSR analysis showed that isolates of the species B. dothidea were separated into 20 groups at a similarity of 100%, each group contains 1～6 isolates, and isolates were catalogued into 2 large groups at a similarity of 50%, which demonstrates that there are genetic diversity under the species level. There is some correlation between hosts and genetic variation and no correlation to geographical distributions.(4) In the rDNA-ITS parsimonious tree, isolate Hc-5-1 and B. obtusa clustered together with 100% boo tstrap value, so the isolate Hc-5-1 was identified as B. obtusa. Pathogenecity test showed that could be a new pathogen of apple white rot, at least to fruits.(5) Morphology of isolate Fx-3-1 is different from other B. dothidea isolates, also located on an independent branch in the rDNA-ITS parsimonious tree. So it was identified as a new species, named Botryosphaeria malicola X.Y. Sun & G.Y. Sun, sp. nov.. and its main characteristics was described: Colonies on PSA showed aerial mycelium and were cottony, dark grayish, conidiomata mostly individual but occasionally aggregated, globose, up to 290-410μm diam, externally dark brown to black. Conidiophores hyaline, cylindrical, thin-walled, septate, base branched, lining the entire inner surface of the conidiomata. Conidiogenous cells holoblastic, hyaline, thin-walled, smooth, and subcylindrical, 14.5-20×3-4μm, producing a single conidium apically, often proliferating at the same level giving rise to periclinal thickenings or rarely proliferating percurrently giving rise to 1-2 annellations. Conidia mostly narrowly straight, fusiform or irregularly fusiform, widest in the middle to upper third, apex subobtuse, base subtruncate, minority fusiform, thinner-walled, hyaline, aseptate, smooth, (21.5-)22.5-25.5(-27)×5-6μm (average of 150 condia 23.7×5.5μm, L/W ratio = 4.3). And the condia produced in cultural similar to those formed in nature, but regularly shaped, longer and appering more narrowly fusiform, (20-) 22-24(25.5)×4-5μm (average of 100 condia 22.4×4.7μm, L/W ratio = 4.8).
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