VIEW ARTICLE

Molecular Plant Pathology

Analysis of the Resistance-Breaking Determinants of Potato Virus X (PVX) Strain HB on Different Potato Genotypes Expressing Extreme Resistance to PVX. M. Querci, International Potato Center, P.O. Box 1558, Lima, Peru; D. C. Baulcombe(2), R. W. Goldbach(3), and L. F. Salazar(4). (2)The Sainsbury Laboratory, Norwich Research Park, Colney, Norwich NR4 7UH, UK; (3)Department of Virology, Agricultural University, Binnenhaven 11, 6709 PD Wageningen, the Netherlands; (4)International Potato Center, P.O. Box 1558, Lima, Peru. Phytopathology 85:1003-1010. Accepted for publication 2 May 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-1003.

Different potato genotypes expressing extreme resistance to potato virus X were inoculated with potato virus X strains cp, CP4, and HB and with three PVX mutants constructed in vitro. Using these viral strains and mutants, the involvement of the coat protein, specifically the single amino acid residue at position 121 within this protein, in the resistance-breaking capacity of strain HB was confirmed for all resistance genes tested. We concluded that the extreme resistance expressed in Solanum × chaucha, S. × curtilobum, S. × juzepczukii, and S. vernei is conferred by Rx genes (Rx_cha, Rx_cur, Rx_juz, and Rx_vrn, respectively) that employ the same mechanism of interaction with the PVX coat protein as Rx, Rx_acl, and Rx_adg. Although S. sucrense clone OCH 11926.4 was resistant to both common PVX strains and PVX_HB, it was susceptible to the mutant isolates. We hypothesized that at least two viral determinants, one of which is not located in the coat protein coding region, interact with the S. sucrense resistance gene.