Virus and Virus-Like Diseases of Citrus and Their Impact on Citrus Production and Germplasm Selection

Abstract

Numerous virus and virus-like diseases affect citrus. Some of the virus, viroid and procaryotic causal agents have been well characterized, but most remain poorly defined. The vector-borne tristeza, greening and stubborn diseases are serious, widespread problems which often limit production in many areas. Virus and virus-like pathogens are transmitted by propagation, by insect vectors, by seed, and mechanically. In some cases the means of natural spread remain unknown. Symptoms vary according to pathogen strain, the host and environment. Graft inoculation of specific indicator plants is still the main identification procedure; however, rapid progress has been made recently with serology and nucleic acid analysis techniques. Control procedures include eradication, certification, use of tolerate or resistant varieties, cross protection, shoot-tip grafting, thermotherapy, and chemotherapy. The complexity of disease factors complicates the already difficult problem of developing useful new citrus varieties.