Abstract:  Alternaria brown spot （Alternaria alternata pv. citri） is a highly destructive disease of tangerines and hybrids of tangerine and grapefruit， or tangerine and orange， which causes defoliation， fruit dropping and dieback， and reduces fruit marketability due to the lesions on the fruit surface. In this paper， the susceptibility of 42 citrus cultivars to this disease were evaluated through inoculating the conidia suspension of A.alternata pv. citri onto the detached young leaves. The result showed that tangerines （Oota ponkan， Xinshengxi No.3 ponkan， Yanxiwanlu ponkan， Hongju 418， Yang xiao 2-6 Nanfengmiju， Ruju， Wuhe Zaoju， Ougan and Mantouhong） were highly susceptible to this pathogen， while Dongjiang Bendizao， Zhuhong and Shatangju showed immunity. Hybrids （Minneola， Orlando， Nova， Kara， Sedoka， Amakusa， Tsunokaori and Murcott） were highly susceptible to A.alternata pv. citri， while Otani-iyo and Nishinoka were slightly susceptible and Ellendale， Hongyugan， Kiyomi， Shiranui and Nankou were immune. Orange， pummelo and lemon were immune to this disease. The susceptibility of other cultivars such as Satsuma， Changshanhuyou and Kumquat remains to be further determined.

Key words: citrus cultivars, Alternaria brown spot of citrus, susceptibility, in vitro evaluation