Psorosis — A Review

P s o r o ~i s ~ as originally describd, is a disease of citrus which induces typical bark scaling lesions in the trunks and limbs of sweet orange, mandarin and grapefruit, and occasionally rinppot s m p t o m s on leaves and fruit. Wmd staining often accompanies bark scaling in infected branches md trunks. Psorasis-infected budwood will induce a variety of symptoms on leaves of inoculatetl indicator seedlmgs of sweet orange, p r a p e h i t or mandarin. These include shock, flecking, vanoun patterns, blotching blisters, ringspots, and chlorosis. D~seases which should not be included in the psorosis complex are concave gum, irnpietratura, aioistacortis, blind pocket, crinkiy leaf, ~nfwtious variegation, Dweet mottle, psorosis-like-pathogens (from Spain), the satsuma dwarf complex of viruses and the seed-transmitted psorosis-like disease reported from Florida. These diseases can be separated from psorosis by symptoms in field trees, by reaction on indicator plants and by cross protection tests using psorosis-E lesion i n d u m as the challenge inoeulum. Cross p r o m i o n still remains the reliable standard for judgingrelationship to psorosis. Psomsis is spread primarily by man viainfected propagative budwood. Natural spread has been shown but a vector has not been identified. Seed transmission has not been demonstrated. Recent studies implicate two different vhrus particles for psomis; a unique flexuous two component virus containinga 48-kd capsid protein and a flexuous rod-shaped carlavirus-like particle containing a 29ckd protein (Levy & Gumpf, 43). Mechanical and graft transmissions were done by Garnseg and Timmer (37) from infeded sweet orange to citmn, then from citronto various herbaceous hostsand ultimately from herbaceous hosts backtosweetomnge which laterdevebped typical psorosis-R lesions.