Reaction of Gou Tou Orange to the Citrus Nematode, Phytophthora, and Citrus Tristeza Virus

Abstract

The rootstock cultivar Gou Tou sour orange was evaluated for tolerance to the citrus nematode (Tylenchulus semipenetrans), Phytophthora nicotianae var. parasitica, P. cit-rophthora and citrus tristeza virus (CTV) in glasshouse and field studies. Gou Tou exhibited high levels of tolerance to P. nicotianae var. parasitica and P. citrophthora, alone or in combination with T. semipenetrans. Gou Tou supported higher root and soil levels of T. semipenetrans than rough lemon plants, without reducing feeder root mass. The ability of Gou Tou to withstand Phytophthora root rot and the citrus nematode was similar in field and glasshouse studies. In a field trial under natural CTV pressure, Gou Tou was compared to conventional Florida sour orange, as a rootstock for sweet orange. After 5 yr, Valencia sweet orange trees on Gou Tou rootstock were slightly affected by a severe CTV isolate. The same isolate killed similar trees on Florida sour orange rootstock. Gou Tou developed stem pitting even if inoculated with a mild CTV isolate.