Combination Breeding and Marker-Assisted Selection to Develop Late Blight Resistant Potato Cultivars

(1) Background: Although resistance to pathogens and pests has been researched in many potato cultivars and breeding lines with DNA markers, there is scarce evidence as to the efficiency of the marker-assisted selection (MAS) for these traits when applied at the early stages of breeding. A goal of this study was to estimate the potential of affordable DNA markers to track resistance genes that are effective against the pathogen Phytophthora infestans (Rpi genes), as a practical breeding tool on a progeny of 68 clones derived from a cross between the cultivar Sudarynya and the hybrid 13/11-09. (2) Methods: this population was studied for four years to elucidate the distribution of late blight (LB) resistance and other agronomical desirable or simple to phenotype traits such as tuber and flower pigmentation, yield capacity and structure. LB resistance was phenotypically evaluated following natural and artificial infection and the presence/absence of nine Rpi genes was assessed with 11 sequence-characterized amplified region (SCAR) markers. To validate this analysis, the profile of Rpi genes in the 13/11-09 parent was established using diagnostic resistance gene enrichment sequencing (dRenSeq) as a gold standard. (3) Results: at the early stages of a breeding program, when screening the segregation of F1 offspring, MAS can halve the workload and selected SCAR markers for Rpi genes provide useful tools

Resistance to silver scurf in wild potato species

Silver scurf caused by Helminthosporium solani Dur. et Mont. has been observed in Northwestern Russia from year to year, but from mid of 90th the amount of the affect of this disease on potato increased. To decrease disease development in potato fields the incorporation of resistance into improved cultivars from highly resistant genotypes is a one of the most promising strategies. Wild potato species is a good source of resistance genes to a large amount of diseases. In order to identify potato wild species which are resistant to silver scurf three year observation of tuber had been conducted. Vegetative seasons with higher temperatures are characterized by more intensive disease development. Disease symptom development on tubers of the same accessions varied in intensity depending on year (LSD = 1,32). During full period of evaluation of large wild potato species (50) and their accession (352) number, the tubers of only individual accesions were symptom free. Such accessions were found within the following species: S. cardiophyllum (2 accessions), S. chancayense (1 accession), S. jamesii (1 accession), S. pinnatisectum Dun. (1 accession), S. stenophyllidium (1 accession) and S. tarijense (1 accession). During three year observation tubers with weak disease symptoms were noted into part of: S. arnezii, S. brachistotrichum, S. cardiophyllum, S. chacoense, S. commersonii, S. famatinae, S. fendleri, S. gibberulosum, S. gourlayi, S. incamayoense, S. jamesii, S. leptostigma, S. kurtzianum, S. maculae, S. papita, S. pinnatisectum, S. piuranum, S. polytrichon, S. spegazzinii, S. stenophyllidium, S. stoloniferum, S. sucrense, S. tarijense, S. toralapanum, S. venturii and S. vernei accessions. Large shares of the accessions with weak disease development were found within the species: S. cardiophyllum (14 of 25 evaluated), S. famatinae (3 of 3), S. jamesii (11 of 19), S. megistacrolobum (4 of 6), S. spegazzinii (8 of 29). The polymorphism for resistance to Phytophthora infestans is present in majority of wild potatoes is also their characteristics for resistance to H. solani. As highly polymorphic for resistance to silver scurf the following species: S. chacoense, S. fendleri, S. hjertingii, S. jamesii, S. kurtzianum, S. pinnatisectum, S. polytrichon and S. spegazzinii were identified. The majority of wild potatoes are considered to be polymorphic for resistance to Phytophthora infestans (Zoteyeva, 1986, 2006). The accession distribution within the species and within the accessions by resistance levels indicates intra specific and intra population polymorphism for resistance to H. solani too.vo

Diversity of Late Blight Resistance Genes in the VIR Potato Collection

Late blight (LB) caused by the oomycete Phytophthora infestans (Mont.) de Bary is the greatest threat to potato production worldwide. Current potato breeding for LB resistance heavily depends on the introduction of new genes for resistance to P. infestans (Rpi genes). Such genes have been discovered in highly diverse wild, primitive, and cultivated species of tuber-bearing potatoes (Solanum L. section Petota Dumort.) and introgressed into the elite potato cultivars by hybridization and transgenic complementation. Unfortunately, even the most resistant potato varieties have been overcome by LB due to the arrival of new pathogen strains and their rapid evolution. Therefore, novel sources for germplasm enhancement comprising the broad-spectrum Rpi genes are in high demand with breeders who aim to provide durable LB resistance. The Genbank of the N.I. Vavilov Institute of Plant Genetic Resources (VIR) in St. Petersburg harbors one of the world’s largest collections of potato and potato relatives. In this study, LB resistance was evaluated in a core selection representing 20 species of seven Petota series according to the Hawkes (1990) classification: Bulbocastana (Rydb.) Hawkes, Demissa Buk., Longipedicellata Buk., Maglia Bitt., Pinnatisecta (Rydb.) Hawkes, Tuberosa (Rydb.) Hawkes (wild and cultivated species), and Yungasensa Corr. LB resistance was assessed in 96 accessions representing 18 species in the laboratory test with detached leaves using a highly virulent and aggressive isolate of P. infestans. The Petota species notably differed in their LB resistance: S. bulbocastanum Dun., S. demissum Lindl., S. cardiophyllum Lindl., and S. berthaultii Hawkes stood out at a high frequency of resistant accessions (7–9 points on a 9-point scale). Well-established specific SCAR markers of ten Rpi genes—Rpi-R1, Rpi-R2/Rpi-blb3, Rpi-R3a, Rpi-R3b, Rpi-R8, Rpi-blb1/Rpi-sto1, Rpi-blb2, and Rpi-vnt1—were used to mine 117 accessions representing 20 species from seven Petota series. In particular, our evidence confirmed the diverse Rpi gene location in two American continents. The structural homologs of the Rpi-R2, Rpi-R3a, Rpi-R3b, and Rpi-R8 genes were found in the North American species other than S. demissum, the species that was the original source of these genes for early potato breeding, and in some cases, in the South American Tuberosa species. The Rpi-blb1/Rpi-sto1 orthologs from S. bulbocastanum and S. stoloniferum Schlechtd et Bché were restricted to genome B in the Mesoamerican series Bulbocastana, Pinnatisecta, and Longipedicellata. The structural homologs of the Rpi-vnt1 gene that were initially identified in the South American species S. venturii Hawkes and Hjert. were reported, for the first time, in the North American series of Petota species