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

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.

Importance of Potato as a Crop and Practical Approaches to Potato Breeding.

Potatoes (Solanum tuberosum L. subsp. tuberosum and andigena) and seven other related species, which are cultivated today, have become the most important non-cereal crop in the world. It is grown on a significant scale in 130 countries, with a gross production value of 63.6 billion US dollars in 2016, with the yearly potato production of 368 million tons in 2018. Today potato is grown for food, animal feed, industrial uses, and seed tuber production, depending on the region, country development, and historical reasons. The food production is both for fresh ware markets and for processing into crisps, french fries, canned potatoes, flakes, etc. More than 10,000 potato varieties have been grown worldwide to date, many of which are still grown. Despite such a large number of varieties, there is still a need for new varieties. Classical breeding of new potato varieties in many programs around the world has changed little in decades and differs mainly in terms of scope and technologies used. Until the turn of the millennium, it was based primarily on empirical experience and selection of individual phenotypic traits. The great genetic diversity that exists in potato and its wild relatives is both an opportunity and a challenge to introduce traits that do not currently exist in the potato gene pool into modern potato varieties. Molecular marker technology development has reached the point where published markers for use in commercial breeding are available. Markers can be used during the whole selection process, with an even more important role of molecular breeding in pre-breeding programs and creation of the most appropriate parental lines.

Ploidy and morphological characteristics of Solanum tuberosum x Solanum phureja hybrids.

In attempt to induce doubled haploids in potato we studied interspecific hybrids between tetraploid Solanum tuberosum cultivars Igor, Jana, Vesna, Romano, Arinda, Fianna, Donald and Vital and Solanum phureja (clone IVP 48). Four out of eight cultivars produced 21 berries in total and 149 seedlings were obtained. Their ploidy was measured using flow cytometry. Analysis revealed 137 tetraploids, 10 triploids and 2 haploids. One haploid, 6 triploids and most of the tetraploids produced tubers. Nine out of 10 triploids were produced in a cross between cv. Igor and S. phureja. The vigour of the haploid plant was weak and produced characteristic long light yellow tubers. Triploid plants were characterized by a dark violet coloration of the stem, which was the same as the coloration of the S. phureja. Tubers had violet skin colour of various intensities and deep eyes. The majority of the tetraploid plants (135) were phenotypically similar to the S. tuberosum, while two plants had a similar violet stem and tubers as the triploids. Triploids were interspecific hybrids and tetraploids were produced by spontaneous chromosome doubling from S. tuberosum gametes. Two tetraploid plants expressing violet coloration might have been interspecific hybrids formed from 2n S. phureja gametes. Further studies are needed to confirm these assumptions.