Submitted to: Subtropics newsletter
Publication Type: Popular Publication
Publication Acceptance Date: 12/8/2007
Publication Date: 12/31/2007
Citation: Rangel, B., Krueger, R. 2007. Stubborn Disease of Citrus in California, Subtropics newsletter. 5(4):2-5, 2007, Trade Publication.p Interpretive Summary: This paper is aimed at growers and nursery persons. Stubborn disease of citrus is a production constraint in many arid and semi-arid production areas. The classical symptoms include stunting, shortened internodes, and small, mis-shapen, unmarketable fruit. The effect on fruit makes this an economic issue for some growers. Stubborn is caused by a bacterium, Spiroplasma citri, and vectored by various leaf hoppers, in California the most important of which is the beet leaf hopper. Stubborn has a number of alternate hosts that may be somewhat removed from the production area and this increases the difficulty of control. The paper expands upon these topics in more depth and makes information on control or management that may be useful to growers.
Technical Abstract: This paper is aimed at growers and nursery persons. It reviews the biology and phytopathology of citrus stubborn disease, and provides an update of our recent activities in this area. Stubborn disease of citrus was first reported in Redlands, California in 1918. However, the causal agent was not identified until the early 1970s. The causal agent, Spiroplasma citri, is a bacterium that also affects other crop and non-crop species. It is vectored by leafhoppers (in California, predominantly by the beet leafhopper). In California, the main reservoir over the winter is in the vector and native alternate hosts. This is the source of most of the infections that occur in citrus. There is little citrus to citrus spread after trees reach about 6 years of age. Symptoms include fruit and foliar symptoms, which are useful diagnostics. More precise diagnosis is by biological indexing, culture, and PCR. We have improved the usefulness of the PCR technique and devised a preliminary sampling methodology. Stubborn is controlled by the use of pathogen-tested propagative material, protected bud sources, and control of the vector and of alternate hosts. We have made a number of useful observations and also documented genetic diversity in California isolates of S. citri.