A psorosis-like agent may be associated with Rio Grande gummosis disease of Citrus
Rio Grande gummosis is a serious disease in Florida on grapefruit (Citrus paradisi). This disorder is also called Florida gummosis and, in California, ferment gum disease. It is characterized by cracks in the bark which release yellow gum. Over the years, affected trees generally become unproductive and may die. Recently, the incidence of Rio Grande gummosis has increased in the Indian River region of Florida (3 to 74 % of diseased trees in surveyed orchards). The causal agent of the disease is not know and several causes have been suggested: fungi (e.g. Physalospora rhodina) or high chloride content in irrigation water. As symptoms resemble citrus psorosis (but with less gumming from bark cracks and callus tissue is formed beneath bark cracks), it was felt that citrus psorosis could be involved in this disorder. It may be recalled that the etiology of citrus psorosis is still unclear; psorosis A and psorosis B (citrus ringspot virus – EU Annex II/A1) have been described and there is uncertainty on whether these two forms correspond to strains of the same virus or to different pathogens. Trees from commercial orchards, showing symptoms of Rio Grande gummosis and asymptomatic trees were indexed on indicator plants. Results showed that 79% and 31 % of the commercial grapefruit and scion trees, respectively, contained a psorosis-like agent. This study does not demonstrate that a psorosis-like agent is responsible for Rio Grande gummosis, but it leaves open the possibility that such an agent might be a factor in this disorder.
Sources
Powell, C.A.; Pelosi, R.R.; Sonoda, R.M.; Lee, R.F. (1998) A psorosis-like agent prevalent in Florida’s grapefruit groves and budwood sources.
Plant Disease, 82(2), 208-209.