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A Destructive New Disease of Citrus in China Caused by Cryptosporiopsis citricarpa sp. nov.

Defoliation, dieback and mortality of Satsuma mandarin (Citrus unshiu), as well as kumquat (Fortunella margarita), in Chenggu County, Shaanxi Province, China was first noticed in 2006 and caused substantial economic losses to citrus production. The incidence of leaves infected approached 100% in some badly infected orchards. The disease prevailed only in late winter and early spring, where early symptoms were rounded and target-like spots on leaves. The disease was named target spot. Black conidiomata were observed on the upper surface of the leaves. A Cryptosporiopsis species was consistently recovered from the infected leaves, shoots, and branches. Koch's postulates were fulfilled by inoculating the conidial suspension of Cryptosporiopsis sp. onto the leaves of Satsuma mandarin. Phylogenetic analysis based on LSU sequence data indicated that this taxon clustered in Cryptosporiopsis (teleomorph: Neofabraea, Dermateaceae). Phylogenetic analysis based on ITS, SSU, and TUB indicated that the isolates of Cryptosporiopsis sp. constituted a distinct clade. Further study also demonstrated that this taxon was morphologically distinct from other species of Cryptosporiopsis, thus suggesting it might belong to an undescribed species. The name Cryptosporiopsis citricarpa sp. nov. is given to accommodate the fungal pathogen in this study.