Characterization of a Zucchini Yellow Mosaic Virus isolate with a deficient helper component
Résumé
Two isolates of zucchini yellow mosaic virus (ZYMV) were found to be either highly (HAT) or poorly (PAT) aphid-transmissible. The inefficient transmission of ZYMV-PAT was independent of the virus source plant or aphid species used. The ZYMV-PAT and ZYMV-HAT, from which the former was derived, did not differ in their host range or serological properties. Purified virions of either ZYMV-HAT or ZYMV-PAT were readily transmitted by aphids when crude or concentrated helper component (HC) from ZYMV-HAT was provided, but were not transmitted when mixed with crude or concentrated HC from ZYMV-PAT. It is concluded that ZYMV-PAT HC is responsible for the defect in aphid transmissibility of this isolate. However a component serologically related to HC was detected both in ZYMV-PAT-infected plants or in ZYMV-PAT RNA in vitro translation products, indicating that an ineffective form of HC is produced by ZYMV-PAT. Furthermore, in in vitro acquisition experiments conducted with ZYMV-PAT and a non-aphid-transmissible isolate (ZYMV-NAT) deficient in the coat protein, high levels of transmission were observed only in the combination containing purified virions of ZYMV-PAT and HC from ZYMV-NAT. This provided additional proof for the deficiencies in the HC for ZYMV-PAT and in the coat protein for ZYMV-NAT.