Abstract
Tristeza, caused by Citrus tristeza virus (CTV), has long been present in Florida but outbreaks of decline on sour orange rootstock were occasional events until the late 1970s. Sour orange rootstock was valued for the high quality of fruit produced and was widely used because of its tolerance of citrus blight, a disease of unknown etiology. Research was directed towards the selection and screening of mild strains of CTV which could protect against sour orange decline strains. Following the introduction of Toxoptera citricida (also known as the brown citrus aphid) in 1995 there was a greater concern for maintaining production of existing blocks of citrus on sour orange rootstock. Availability of the CTV genome sequence around the same time as well as molecular characterization of in planta CTV populations led to the selection of mild CTV isolates which when inoculated into existing field trees, extended the productive life of the groves and enabled a more graduate replanting of trees on CTV-tolerant rootstocks. The history of CTV in Florida and the methods developed to select mild isolates for use for mild strain cross protection will be reviewed.
Highlights
Citrus tristeza virus (CTV) is the most important viral disease of citrus worldwide
Often ropey-like large pits occur on the trunk of trees, especially in grapefruit trees, and while detrimental to tree vigor over time, the economic impact on the tree is usually less than trees showing the small pitting with gum deposits in the pitted area (Bar-Joseph et al, 1989). Another symptom associated with CTV is seedling yellows (CTV-SY) which is expressed by a yellowing on lemon, grapefruit, or sour orange followed by a stunting of growth in these hosts
A standardized host range using Mexican lime, sour orange, Madame vinous sweet orange, and Duncan grapefruit seedlings and a sweet orange budded onto sour orange as standard indicator plants has been developed and used as a method for determining the biological activity of a specific CTV isolate and to enable comparison of biological activities of CTV isolates from various areas of the world (Garnsey et al, 1987, 2005)
Summary
Citrus tristeza virus (CTV) is the most important viral disease of citrus worldwide. Since the first outbreaks in South America in the 1940s, CTV has killed more than 85 million trees worldwide (Lee et al, 1992; Bar-Joseph et al, 2010). Often ropey-like large pits occur on the trunk of trees, especially in grapefruit trees, and while detrimental to tree vigor over time, the economic impact on the tree is usually less than trees showing the small pitting with gum deposits in the pitted area (Bar-Joseph et al, 1989). Another symptom associated with CTV is seedling yellows (CTV-SY) which is expressed by a yellowing on lemon, grapefruit, or sour orange followed by a stunting of growth in these hosts. For CTVSP strains, options can include implementation of mild strain cross protection, development of CTV resistance in commercially desirable cultivars via genetic engineering methods, and/or development of CTV resistance by conventional plant breeding www.frontiersin.org
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