Late Blight Resistance Conferred by Rpi-Smira2/R8 in Potato Genotypes In Vitro Depends on the Genetic Background

Abstract

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

Modern Breeding Strategies and Tools for Durable Late Blight Resistance in Potato

“…Kim et al [ 74 ] demonstrated that in the genotypes MaR8 and MaR9, at least four genes of types R3a , R3b , R4 , and R8 are present, as well as seven of types R1 , Rpi-abpt1 , R3a , R3b , R4 , R8 , R9 , respectively. The Fortuna variety has two pyramided genes, namely Rpi-blb1 and Rpi-blb2 [ 170 ]. The Bzura cultivar harbours two Rpi genes: R2-like and another unknown Rpi gene [ 171 ].…”

Secondary Metabolites, Other Prospective Substances, and Alternative Approaches That Could Promote Resistance against Phytophthora infestans

“…The Sárpo Mira cultivar is one of the few potato cultivars that has been reported to retain resistance in the field for more than a decade. Its genetic origin has not been publicly disclosed, but its genome contains a set of at least five different R genes that confer qualitative and quantitative resistance to late blight [101][102][103]. It has been used in studies of late blight resistance and as a source of resistance in conventional breeding [102,104].…”

“…Its genetic origin has not been publicly disclosed, but its genome contains a set of at least five different R genes that confer qualitative and quantitative resistance to late blight [101][102][103]. It has been used in studies of late blight resistance and as a source of resistance in conventional breeding [102,104]. On average, the traditional potato breeding process takes more than ten years from the initial crossing (Figure 5) to obtaining a new cultivar, but the process can take considerably more time due to a laborious selection process, backcrossing, and the elimination of undesirable quality traits [105].…”