THE RESTRICTED DISTRIBUTION OF POTATO LEAFROLL LUTEOVIRUS ANTIGEN IN POTATO PLANTS WITH TRANSGENIC RESISTANCE RESEMBLES THAT IN CLONES WITH ONE TYPE OF HOST GENE-MEDIATED RESISTANCE

The distribution of virus-infected cells was examined, by fluorescence microscopy, within plants of a range of potato clones infected with potato leafroll luteovirus (PLRV). This range included nine PLRV-resistant clones, of which four were transgenic lines carrying the PLRV coat protein gene and five were conventionally bred. Plants of these clones were resistant to PLRV multiplication and accumulated less virus antigen in leaf tissue than did susceptible clones. Indirect fluorescent antibody staining of thin sections from carbodiimide-fixed petiole tissue revealed that in plants of PLRV-susceptible clones, virus-infected cells were abundant within both external (abaxial) and internal (adaxial) phloem bundles. In plants of the PLRV-resistant conventionally bred clones and in resistant transgenic lines of cv. Pentland Squire, virus-infected cells were much fewer in number and largely restricted to internal phloem bundles. In resistant transgenic lines of cv. Desiree, this restricted distribution of PLRV antigen was only detected in petioles of young leaves. The results suggest that the transgenic and a host-mediated type of resistance that restricts virus multiplication have underlying similarities.