Loquat scab caused by Fusicladium eriobotryae: Elucidating the disease cycle

Abstract

Fusicladium eriobotryae (Cav.) Sacc. is the causal agent of loquat (Eriobotrya japonica Lindl.) scab. The fungus can infect leaves, shoots, and fruits producing circular chlorotic spots, which become olive-colored and velvety as they increase in size. Although F. eriobotryae has been poorly understood, recent studies on the biology of this pathogen and the epidemiology of loquat scab have improved the knowledge about the cycle of the disease. The fungus overwinters on lesions on leaves, branches, or mummified fruits that remain in the tree after harvest. The spores produced in these inoculum sources seem to be the primary inoculum, which can infect young loquat leaves or loquat fruit. The spores are dispersed associated to any measurable rain event (≥0.2 mm), splashing on nearby fruits or leaves, where they germinate and penetrate into the tissue, probably directly through the cuticle or through stomata. Conidia are able to germinate and infect loquat plants over a wide range of temperatures (5-20°C), but at least 12 h of wetness are required. Once the infection has occurred, if the temperature is adequate (5-25°C), the pathogen grows subcuticularly, developing new sporulation. Conidia cause all secondary infections during the entire fruiting season, as long as rains disperse them, and temperature and wetness duration permit their germination and the growth of the lesions.