COMPARISON OF ISOLATES OF CITRUS RINGSPOT, PSOROSIS, AND OTHER VIRUS-LIKE AGENTS OF CITRUS

A collection of graft-transmissible psorosis and psorosislike diseases of citrus were compared with a partially characterized isolate of citrus ringspot virus (CRSV-4) from Florida. Fourteen isolates of citrus ringspot and psorosis from Florida, Spain, and Argentina were mechanically transmissible to Chenopodium quinoa and induced local lesions. The infectivity associated with several isolates was separated into top and bottom components by sucrose gradient centrifugation, which is characteristic of CRSV-4. A 48-kilo dalton (kDa) protein, which is assumed to be the CRSV capsid protein, was detected in preparations of top and bottom components from 13 of the isolates. The 48-kDa protein was not detected in preparations from healthy plants or plants with symptoms of concave gum, cristacortis, or impietratura. Thus, there was a good correlation between the detection of the 48-kDa protein, indicative of a CRSV-type virus, and the designation of diseases as either ringspot or psorosis based on symptoms. An antiserum, produced to purified CRSV-4, was used to detect the 48-kDa protein in western blots and virus particles by serologically specific electron microscopy (SSEM). This is further evidence that the 48-kDa protein is the capsid protein of the virus.