BIOLOGICAL DIVERSITY OF CITRUS RINGSPOT ISOLATES IN SPAIN

Eight isolates of citrus ringspot were selected by symptoms induced in field trees and compared with a citrus psorosis isolate for symptom e xpression on several citrus species under temperature-controlled glass house conditions. Symptom expression in each host isolate combination was quantified by a pathogenicity index (PI) that considered symptom i ntensity and the number of plants showing each symptom. A general path ogenicity index (GPI) was defined for each isolate as a weighted mean of the different PI. A wide range of symptoms could be observed depend ing on host-isolate combination and incubation temperature. On the bas is of symptoms induced in the glasshouse, cross protecting reaction ag ainst psorosis B challenge inoculation, mechanical transmissibility to Chenopodium quinoa, and presence of a c. 48-kDa protein associated to fractions of a sucrose gradient infective on C. quinoa (Navas-Castill o et al, 1993), six of the ringspot isolates (RS-ALC, RS-SOR, RS-GR, R S-INV, RS-CV and RS-SR) could not be distinguished from the psorosis i solate used as control, whereas the other two isolates (RS-ALM and RS- BUR) were clearly different. Field symptoms induced by these two isola tes also differed from those induced by psorosis or by the other rings pot isolates.