Late Blight Resistance Evaluation and Genome-Wide Assessment of Genetic Diversity in Wild and Cultivated Potato Species

Late blight, caused by the oomycete Phytophthora infestans, is the most devastating disease in potato-producing regions of the world. Cultivation of resistant varieties is the most effective and environmentally friendly way to control potato late blight disease, and identification of germplasms with late blight resistance and clarification their genetic relationship would promote the development of the resistant varieties. In this study, a diverse population of 189 genotypes with potential late blight resistance, consisting of 20 wild species and cultivated Solanum tuberosum Andigenum group and Chilotanum group, was screened for the presence of late blight resistance by performing challenge inoculation with four Phytophthora infestans isolates including one 13_A2 isolate, CN152. Ten elite resources with broad-spectrum resistance and 127 with isolate-specific resistance against P. infestans were identified. To improve the available gene pool for future potato breeding programs, the population was genotyped using 30 simple sequence repeat (SSR) markers covering the entire potato genome. A total of 173 alleles were detected with an average of 5.77 alleles per locus. Structure analysis discriminated the 189 potato genotypes into five populations based on taxonomic classification and genetic origin with some deviations. There was no obvious clustering by country of origin, ploidy level, EBN (endosperm balance number) value, or nuclear clade. Analysis of molecular variance showed 10.08% genetic variation existed among populations. The genetic differentiation (Fst) ranged from 0.0937 to 0.1764, and the nucleotide diversity (π) was 0.2269 across populations with the range from 0.1942 to 0.2489. Further genotyping of 20K SNP array confirmed the classification of SSRs and could uncover the genetic relationships of Solanum germplasms. Our results indicate that there exits abundant genetic variation in wild and cultivated potato germplasms, while the cultivated S. tuberosum Chilotanum group has lower genetic diversity. The phenotypic and genetic information obtained in this study provide a useful guide for hybrid combination and resistance introgression from wild gene pool into cultivated species for cultivar improvement, as well as for germplasm conservation efforts and resistance gene mining.

Genome assembly of primitive cultivated potato Solanum stenotomum provides insights into potato evolution

Genetic diversity is the raw material for germplasm enhancement. Landraces and wild species relatives of potato, which contain a rich gene pool of valuable agronomic traits, can provide insights into the genetic diversity behind the adaptability of the common potato. The diploid plant, Solanum stenotomum (Sst), is believed to have an ancestral relationship with modern potato cultivars and be a potential source of resistance against disease. Sequencing of the Sst genome generated an assembly of 852.85 Mb (N50 scaffold size, 3.7 Mb). Pseudomolecule construction anchored 788.75 Mb of the assembly onto 12 pseudochromosomes, with an anchor rate of 92.4%. Genome annotation yielded 41,914 high-confidence protein-coding gene models and comparative analyses with closely related Solanaceae species identified 358 Sst-specific gene families, 885 gene families with expansion along the Sst lineage, and 149 genes experiencing accelerated rates of protein sequence evolution in Sst, the functions of which were mainly associated with defense responses, particularly against bacterial and fungal infection. Insights into the Sst genome and the genomic variation of cultivated potato taxa are valuable in elaborating the impact of potato evolution in early landrace diploid and facilitate modern potato breeding.

Red and Purple Flesh Potatoes a Healthy and Attractive Alternative Associated with New Market Trends

The potato is the fourth most important crop in the world in terms of human food, after maize, wheat and rice (FAOSTAT, 2019). The cultivated potato is a vital food-security crop considering its worldwide growth, from latitudes 65° Lat N to 53° Lat S, high yield, and great nutritive value. The potato is a good source of dietary energy and micronutrients, and its protein content is high in comparison with other roots and tubers. The cultivated potato is also a concentrated source of vitamin C and some minerals such as potassium and magnesium. Tuber flesh color generally ranges from white to dark yellow in cultivated potato; however, the high potato diversity shows tuber flesh color varies from white to dark purple. Red and purple-flesh potatoes are an interesting alternative for consumers due to phenolic compounds and antioxidant capacity. The goal of this publication is to show the advances in red and purple flesh potato, in terms of anthocyanin profile, color extraction and stability in simulated in vitro digestion.

Composition of the collection of primitive cultivated species within the Solanum L. section Petota Dumort. and contemporary trends in their research

The diversity of potato genetic resources in the VIR genebank harbors one of the world’s first collections of primitive cultivated species. These accessions are native potato varieties cultivated by the indigenous population of South America. The oldest accessions in the collection are traced back to 1927. Approximately one fifth of the collection (106 accessions out of 573) is the unique material procured by VIR’s collecting missions to Bolivia, Colombia, Ecuador, and Peru. According to S. Bukasov’s potato classification, the diversity of South American highland potatoes explored by VIR’s collectors belongs to spp. Solanum ajanhuiri Juz. et Buk., S. × chaucha Juz. et Buk., S. mammilliferum Juz. et Buk., S. phureja Juz. et Buk., S. rybinii Juz. et Buk., S. goniocalyx Juz. et Buk., S. stenotomum Juz. et Buk., S. tenuifilamentum Juz. et Buk., S.× juzepczukii Buk., and S. × curtilobum Juz. et Buk. Within this group of species, S. × ajanhuiri, S. phureja and S. stenostomum are the closest in their characteristics to ancient domesticated forms of tuber-bearing Solanum spp. This publication is an analytical review of the current composition of the primitive cultivated potato species collection and the results of its earlier studies. Ecogeographic descriptions of the sites native for cultivated potatoes and information on the sources of the accessions are presented. A large-scale evaluation of primitive cultivated potato accessions by a set of characters, carried out in field and laboratory experiments, uncovers their breeding potential and serves as the primary information platform for further indepth research. Studying S. phureja and closely related cultivated potato species is important for finding solutions of fundamental problems in plant biology. The data arrays accumulated today would facilitate targeted selection among accessions to identify most promising ones for molecular genetic studies into the gene pool diversity of potato species.

Genetic Diversity of Nine Non-Recombinant Potato virus Y Isolates From Three Biological Strain Groups: Historical and Geographical Insights

Potato virus Y (PVY) isolates from potato currently exist as a complex of six biologically defined strain groups all containing nonrecombinant isolates and at least 14 recombinant minor phylogroups. Recent studies on eight historical UK potato PVY isolates preserved since 1984 found only nonrecombinants. Here, four of five PVY isolates from cultivated potato or wild Solanum spp. collected recently in Australia, Mexico, and the U.S.A. were typed by inoculation to tobacco plants and/or serological testing using monoclonal antibodies. Next, these five modern isolates and four additional historical UK isolates belonging to biological strain groups PVYC, PVYZ, or PVYN obtained from cultivated potato in 1943 to 1984 were sequenced. None of the nine complete PVY genomes obtained were recombinants. Phylogenetic analysis revealed that the four historical UK isolates were in minor phylogroups PVYC1 (YC-R), PVYO-O (YZ-CM1), PVYNA-N (YN-M), or PVYEu-N (YN-RM), Australian isolate YO-BL2 was in minor phylogroup PVYO-O5, and both Mexican isolate YN-Mex43 and U.S.A. isolates YN-MT12_Oth288, YN-MT12_Oth295, and YN-WWAA150131G42 were in minor phylogroup PVYEu-N. When combined, these new findings and those from the eight historical UK isolates sequenced earlier provide important historical insights concerning the diversity of early PVY populations in Europe and the appearance of recombinants in that part of the world. They and four recent Australian isolates sequenced earlier also provide geographical insights about the geographical distribution and diversity of PVY populations in Australia and North America.

Development of chromosome-specific markers for a study on introgressive hybridization of potato with the wild Mexican allotetraploid species Solanum stoloniferum Schltdl

In order to involve valuable germplasm of the wild Mexican allotetraploid potato species Solanum stoloniferum Schltdl. (genomic composition ААВВ) into breeding, pentaploid interspecific hybrids (ААAAВ) with cultivated potato S. tuberosum L. (АААА) and their backcross progenies are usually used. Homologous synapsis in meiosis of such hybrids is expected only between chromosomes of the A subgenome, therefore a question arose about a possibility of introgressing genetic material of the subgenome B into the A genome of cultivated potato. In this connection, development of various schemes for the B subgenome introgression into the genome of cultivated potato is considered as a topical issue. The previous research has yielded four schemes of S. stoloniferum involvement into breeding, which imply backcrossing with cultivated potato of the following interspecific hybrids: (1) hexaploids (genomic composition ААААВВ, the conventional introgression scheme), (2) tetraploids (putatively, АААВ), (3) self-pollination progeny of a 4x hybrid and (4) pentaploid hybrids with a putative genome composition of АААВВ. The present paper presents the first results of the development of chromosome-specific DNA markers for the identification of S. stoloniferum chromosomes in interspecific hybrids. An S. stoloniferum accession PI 205522 with a high degree of resistance to late blight and PVY had been found to possess several DNA-markers of the R-genes conferring resistance to these pathogens and was used in hybridization as a promising parent. A set of 23 SSR- and CAPS markers with the known chromosome location in S. tuberosum was generated. These markers detect polymorphism between parent genotypes, i.e., the diploid clone IGC 10/1.21 of cultivated potatoes S. tuberosum, and accession PI 205522 of S. stoloniferum. All the markers specific for the wild species were found in triploid (ААВ) and pentaploid (АААВВ) hybrids of S. stoloniferum × S. tuberosum. This set of markers will be used for efficiency assessment of different schemes for S. stoloniferum genetic material introgression into the obtained BC2-BC3 generations after crossing the interspecific hybrids with cultivated potato.

Microencapsulation of Anthocyanin Extracted from Purple Flesh Cultivated Potatoes by Spray Drying and Its Effects on In Vitro Gastrointestinal Digestion

Purple flesh cultivated potato (PP) is a foodstuff scarcely cultivated in the world but with high potential because of its anthocyanin content. Moreover, it has been little explored as a source of anthocyanins (AT) for further applications in formulated food products. The main goal of this research was to study the effect of maltodextrin (MD) and spray drying conditions on the encapsulation efficiency (EE) and bioaccesibility of AT from purple flesh cultivated potato extract (PPE). The anthocyanin-rich extract was obtained from PP and microencapsulated by spray-drying, using MD as the encapsulating agent. A statistical optimization approach was used to obtain optimal microencapsulation conditions. The PPE microparticles obtained under optimal conditions showed 86% of EE. The protector effect of microencapsulation on AT was observed to be stable during storage and in vitro digestion. The AT degradation rate constant was significantly lower for the PPE-MD than for the PPE. The assessed bioaccesibility of AT from the PPE-MD was 20% higher than that of the PPE, which could be explained by the protective effect of encapsulation against environmental conditions. In conclusion, microencapsulation is an effective strategy to protect AT from PP, suggesting that AT may be an alternative as a stable colorant for use in the food industry.