Potato (<i>Solanum tuberosum</i> L.) is an important staple food and economic crop in many countries. It is of critical importance to understand the genetic diversity and population structure for effective collection, conservation, and utilization of potato germplasm. Thus, the objective of the present study was to investigate the genetic diversity and population structure of potato germplasm conserved in the National Agrobiodiversity Center (NAC) of South Korea to provide basic data for future preservation and breeding of potato genetic resources. A total of 24 simple sequence repeat (SSR) markers were used to assess the genetic diversity and population structure of 482 potato accessions. A total of 257 alleles were detected, with an average of 10.71 alleles per locus. Analysis of molecular variance showed that 97% of allelic diversity was attributed to individual accessions within the population, while only 3% was distributed among populations. Results of genetic structure analysis based on STRUCTURE and discriminant analysis of principal components revealed that 482 potato accessions could be divided into two main subpopulations. Accessions of subpopulation 1 mainly belonged to cultivars and breeding lines. Accessions of subpopulations 2 basically corresponded to wild relatives of potatoes. Results of this study provide useful information for potato improvement and conservation programs, although further studies are needed for a more accurate evaluation of genetic diversity and phenotypic traits of potatoes.

Abstract China is the world’s largest producer of sweet potato (Ipomoea batatas (L.) Lam.). Considering that there are numerous sweet potato-producing regions in China and sweet potato is a vegetatively propagated crop, the genetic diversity of sweet potato viruses could be high in the country. However, studies on species and genetic variabilities of sweet potato viruses in China are limited, making it difficult to prevent and control viral diseases in this crop. During 2014–2019, sweet potato samples with viral disease-like symptoms were randomly collected from sweet potato fields in 25 provinces in China. Twenty-one virus species, including 12 DNA and 9 RNA viruses, were identified in the samples using next-generation sequencing, polymerase chain reaction and rolling-circle amplification methods. One novel sweepovirus species, Sweet potato leaf curl Hubei virus (SPLCHbV), was identified. Two species, Sweet potato collusive virus and Tobacco mosaic virus, were identified for the first time in sweet potato in China. Full-length or nearly full-length genomic sequences of 111 isolates belonging to 18 viral species were obtained. Genome sequence comparisons of potyvirus isolates obtained in this study indicate that the genome of sweet potato virus 2 is highly conserved, whereas the other four potyviruses, sweet potato feathery mottle virus, sweet potato virus G, sweet potato latent virus and sweet potato virus C, exhibited a high genetic variability. The similarities among the 40 sweepovirus genomic sequences obtained from eight sweepovirus species are 67.0–99.8%. The eight sweepoviruses include 14 strains, of which 4 novel strains were identified from SPLCHbV and 1 from sweet potato leaf curl Guangxi virus. Five sweet potato chlorotic stunt virus (SPCSV) isolates obtained belong to the WA strain, and the genome sequences of SPCSV are highly conserved. Together, this study for the first time comprehensively reports the variability of sweet potato viruses in China.

The composition of Potato virus Y strains found on the territory of Belarus, as well as the molecular variability of their genomes, was studied. The presence of strains PVYᴺᵀᴺ (genotype A) and PVYᴺW (genotypes A and B) was shown. The degree of the identity between individual genome regions of the studied isolates ranges from 100 to 97.33%. Nucleotides that are under purifying selection were revealed in the sequences.

The present work considered collecting and characterizing the genetic diversity of sweet potato [Ipomoea batata (L.) Lam.] in Ecuador through morphological and molecular descriptors (SSRs). Germplasm collections were made to assemble a national sweet potato collection for Ecuador. Characterization of the genetic diversity of this species was done through 34 morphological descriptors (24 qualitative and 10 quantitative), plus 12 exclusive descriptors for flowering and 8 microsatellites (SSRs). Three hundred and sixty-eight sweet potato accessions were collected in 18 provinces of Ecuador. Morphological characterization showed seven morphological groups and the variables with the greatest discriminating power for the description of the germplasm (p < .001) were the color, shape and defects of the reservoir root, in addition to the shape of the profile and lobes of the leaves. Principal component analysis determined the association of the main quantitative morphological features to the components. Eight microsatellite markers detected 89 alleles, with an average of 11.12 allele/locus and average polymorphism (PIC) of 0.848. STRUCTURE software revealed the formation of 4 different genetic groups. Morphological and molecular data did not show the formation of any group defined according to the province of origin. Factors such as the sweet potato reproductive system (cross-pollination), random sweet potato mutations and farmer exchange, contributed to the greater genetic diversity present. High genetic diversity and low number of duplicates were identified. This collection could provide outstanding genotypes to be used in breeding programs. Local landraces still in the hands of local farmers suggest that in situ conservation projects must be put in place.

Specialty potatoes, particularly rich in nutrients have gained importance in recent times which has leadformulation of separate breeding programs. Characterizing the genetic base of essential cultivars in any crop is veryimportant for the breeders to utilize and improve it through these breeding programs. Forty one Indian potato cultivarscharacterized for their total carotenoid content were grouped into two, 24 with low carotenoid (≤ 100 μg/100g f.w.) contentand 17 with medium (100 - 350 μg/100g f.w.), based on their total carotenoid content. Twenty four nuclear microsatellitemarkers were used to assess the genetic diversity present within and between the different groups which generated a totalof 177 alleles with an average of 7.37 per loci and 4.01 per genotype. Four alleles were found specific to potato cultivarswith low carotenoids content, whereas, none were found specific to medium carotenoids containing cultivars. Geneticdiversity among the low carotenoid varieties was found to be higher (2.31) than the medium containing (2.26). The clusteranalysis grouped all the 41 varieties into 2 main clusters and 4 sub clusters with no clear relation between diversity andtotal carotenoid content. The average proportion of diversity present within the Indian potato cultivars (low + medium)was found to be 98%, whereas, the proportion of diversity between the cultivars of low and medium carotenoid containingwas found to be very low (2%). The analyzed diversity among the different carotenoid containing Indian potato cultivarswould be of great help to breeders as many of these are used as parents to develop new and improved potato varieties.

As a consequence of climate change, heat waves in combination with extended drought periods will be an increasing threat to crop yield. Therefore, breeding stress tolerant crop plants is an urgent need. Breeding for stress tolerance has benefited from large scale phenotyping, enabling non-invasive, continuous monitoring of plant growth. In case of potato, this is compromised by the fact that tubers grow belowground, making phenotyping of tuber development a challenging task. To determine the growth dynamics of tubers before, during and after stress treatment is nearly impossible with traditional destructive harvesting approaches. In contrast, X-ray Computed Tomography (CT) offers the opportunity to access belowground growth processes. In this study, potato tuber development from initiation until harvest was monitored by CT analysis for five different genotypes under stress conditions. Tuber growth was monitored three times per week via CT analysis. Stress treatment was started when all plants exhibited detectable tubers. Combined heat and drought stress was applied by increasing growth temperature for 2 weeks and simultaneously decreasing daily water supply. CT analysis revealed that tuber growth is inhibited under stress within a week and can resume after the stress has been terminated. After cessation of stress, tubers started growing again and were only slightly and insignificantly smaller than control tubers at the end of the experimental period. These growth characteristics were accompanied by corresponding changes in gene expression and activity of enzymes relevant for starch metabolism which is the driving force for tuber growth. Gene expression and activity of Sucrose Synthase (SuSy) reaffirmed the detrimental impact of the stress on starch biosynthesis. Perception of the stress treatment by the tubers was confirmed by gene expression analysis of potential stress marker genes whose applicability for potato tubers is further discussed. We established a semi-automatic imaging pipeline to analyze potato tuber delevopment in a medium thoughput (5 min per pot). The imaging pipeline presented here can be scaled up to be used in high-throughput phenotyping systems. However, the combination with automated data processing is the key to generate objective data accelerating breeding efforts to improve abiotic stress tolerance of potato genotypes.

The common potato, Solanum tuberosum L. (2n = 4x = 48), has 100–200 related wild taxonomic species endemic to the Americas, which constitute invaluable sources of genetic diversity. They form a polyploid series with 2n = 2x – 6x (x = 12) and can reproduce asexually by tubers and stolons and/or sexually by seeds. Information is scarce on their preponderant mode of reproduction and its consequences on the genetic population structure over time. In previous work, a morphologically variable wild potato population from northwestern Argentina was sampled in two consecutive years. Two populations were ex situ regenerated from the sampled propagules (seeds in 2013 and tubers in 2014) for morphological and reproductive studies; these populations exhibited differences in reproductive behavior that could not be related to morphological phenotypes. To ascertain if the observed differences could be related to the captured genetic diversity in each year, a molecular analysis was carried out with seven microsatellite primer pairs located in seven chromosomes of the basic set. The captured genetic diversity, based on the proportion of individuals with a unique pattern of amplified fragments, varied significantly (χ² α = .05) between sampling years. This could be due to changes in the preponderant mode of reproduction, differential genotype fitness resulting from genotype × environment interactions, or both. Wild potato accessions at germplasm banks are one‐time collection samples; thus, they may not be representative of the genetic diversity of the sampled population. To properly ex situ conserve the available genetic diversity, it is advisable to resample the sites whenever possible and to conform each accession with the successive samples.

2021

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.

We determined the species composition of 219 isolates of potato blackleg or soft rot pathogens in Japan collected after 2000 from potato plants by species-specific PCR. Of the total, Pectobacterium wasabiae (Pw) and P. carotovorum subsp. brasiliense (Pcb) comprised 88% (Pw: 94 isolates, Pcb: 98 isolates) of the isolates and Dickeya dianthicola (Ddi) 12% (27 isolates). P. atrosepticum (Pa) was not detected. Genetic diversity of Pw, Pcb and Ddi was investigated using repetitive sequence-based PCR (rep-PCR) fingerprinting with three primer pairs complementary to repetitive sequences in the bacterial genome (BOX, ERIC and REP). One hundred and twenty-one Pw isolates, one hundred Pcb isolates and thirty-three Ddi isolates were assigned to twenty-nine, twenty-one and eleven fingerprint genotypes (FGs) based on the combination of fingerprint patterns for each rep-PCR experiment (BOX-, ERIC- and REP-PCR). The genetic diversity of Pw and Ddi isolates in Japan was considered high, with Simpson’s diversity index and Shannon’s index of 0.87 and 2.44 for Pw, and 0.84 and 2.05 for Ddi, respectively. Pcb isolates were less diversified genetically (diversity index: 0.57 and 1.58). The FGs of the isolates obtained from blackleg-affected potato plants in the seed tuber field agreed with those of the isolates in the field where the seeds produced were grown. These results support the occurrence of seed-borne transmission of the blackleg pathogen between the fields.