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 expression on several citrus species under temperature-controlled glasshouse conditions. Symptom expression in each host-isolate combination was quantified by a pathogenicity index (PI) that considered symptom intensity and the number of plants showing each symptom. A general pathogenicity index (GPI) was defined for each isolate as a weighted mean of the different PI. A wide range of symptoms could be observed depending on host-isolate combination and incubation temperature. On the basis of symptoms induced in the glasshouse, cross protecting reaction against 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-Castillo et al, 1993), six of the ringspot isolates (RS-ALC, RS-SOR, RS-GR, RS-INV, RS-CV and RS-SR) could not be distinguished from the psorosis isolate used as control, whereas the other two isolates (RS-ALM and RS-BUR) were clearly different. Field symptoms induced by these two isolates also differed from those induced by psorosis or by the other ringspot isolates.