Evaluation of Citrus Cultivars Susceptibility to Leaf Spot Disease Caused by Alternaria alternata under in vitro Conditions

Alternaria brown spot is a serious disease of fruit and foliage of citrus. This disease caused by Alternaria alternata and causes serious economical losses on susceptible cultivars in Iran. In this research, susceptibility of seven citrus cultivars including Fortune, Orlando tangelo, Mineola tangelo, Page, Clementine, Sour orange and Sweet orange (Thomson) fruits to A. alternata was investigated. The result revealed that the Fortune, Orlando tangelo, Mineola tangelo, Page and Thomson fruits are highly susceptible and showed severe symptoms of brown spot, especially in “unwounded” fruits. In contrast, Clementine and Sour orange are resistant to this pathogen, and A. alternata could not grow on unwounded fruits. However, weak symptoms were observed in Clementine and Sour orange when cuticle was broken and flavedo or flavedo + albedo was removed.