Polymerase chain reaction amplification of DNA from various strains of Xylella fastidiosa with tRNA consensus primers produced three different fingerprint groups. The citrus variegated chlorosis (CVC) and mulberry leaf scorch strains were unique and readily separated from each other and all other strains tested. Internal primers were designed based on the sequence of a DNA fragment unique to the CVC strain. An assay was developed with a mixture of these primers and those reported to detect 18 strains of X. fastidiosa. The assay was used to survey citrus in Brazil. The strain identified to be the cause of CVC was found in constant association with trees with CVC symptoms. On occasion, trees with no symptoms were found to have the CVC strain; this was presumably due to presymptomatic infections. No other strains were found in this survey, and X. fastidiosa was not associated with citrus blight.
Rio Grande Gummosis (RGG) is one of the most serious diseases of grapefruit in the Indian River region of Florida. Experiments were conducted to determine if a graft-transmissible agent was associated with this disease in commercial grapefruit, and if any such agent was present in scion sources used for grapefruit propagation. Indexing data from indicators revealed that 79% and 31% of the commercial grapefruit and scion trees, respectively, contained a psorosis-like agent (PLA). The PLA was present in both RGG-affected and symptomless trees. We conclude that Florida's grapefruit propagation sources are contaminated with a PLA that is now widespread in commercial plantings.
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