| Summary: | Potato production worldwide is threatened by late blight, caused by the oomycete <i>Phytophthora infestans</i> (Mont.) de Bary. Highly resistant potato cultivars were developed in breeding programs, using resistance gene pyramiding methods. In Sárpo Mira potatoes, five resistance genes (<i>R3a</i>, <i>R3b</i>, <i>R4</i>, <i>Rpi-Smira1</i>, and <i>Rpi</i>-<i>Smira2/R8</i>) are reported, with the latter gene assumed to be the major contributor. To study the level of late blight resistance conferred by the <i>Rpi-Smira2/R8</i> gene, potato genotypes with only the <i>Rpi-Smira2/R8</i> gene were selected from progeny population in which susceptible cultivars were crossed with Sárpo Mira. Ten <i>R8</i> potato genotypes were obtained using stepwise marker-assisted selection, and agroinfiltration of the avirulence effector gene <i>Avr4</i>. Nine of these <i>R8</i> genotypes were infected with both Slovenian <i>P. infestans</i> isolates and aggressive foreign isolates. All the progeny <i>R8</i> genotypes are resistant to the Slovenian <i>P. infestans</i> isolate 02_07, and several show milder late blight symptoms than the corresponding susceptible parent after inoculation with other isolates. When inoculated with foreign <i>P. infestans</i> isolates, the genotype C571 shows intermediate resistance, similar to that of Sárpo Mira. These results suggest that <i>Rpi-Smira2/R8</i> contributes to late blight resistance, although this resistance is not guaranteed solely by the presence of the <i>R8</i> in the genome.
|
|---|