A considerable number of highly diverse species exist in genus Solanum. Because they can adapt to a broad range of habitats, potato wild relatives are promising sources of desirable agricultural traits. Potato taxonomy is quite complex because of introgression, interspecific hybridization, auto- and allopolyploidy, sexual compatibility among many species, a mixture of sexual and asexual reproduction, possible recent species divergence, phenotypic plasticity, and the consequent high morphological similarity among species. Recent researchers using molecular tools have contributed to the identification of genes controlling several types of resistance as well as to the revision of taxonomical relationships among potato species. Historically, primitive forms of cultivated potato and its wild relatives have been used in breeding programs and there is still an enormous and unimaginable potential for discovering desirable characteristics, particularly in wild species Different methods have been developed to incorporate useful alleles from these wild species into the improved cultivars. Potato germplasm comprising of useful alleles for different breeding objectives is preserved in various gene banks worldwide. These materials, with their invaluable information, are accessible for research and breeding purposes. Precise identification of species base on the new taxonomy is essential for effective use of the germplasm collection.

Morphology has long provided key data to assess diversity in landrace collections in genebanks worldwide. We explored, through an F2 cross between two inbred diploid potato clones, the utility of tuber morphology to assess diversity of potato landraces. We assessed the F2 population created by self-pollinating an F1 clone from a cross between two diploid (2n = 2x = 24) potato clones: DM, a completely homozygous clone derived from somatically doubling an androgenic monoploid of a cultivated potato, and M6, a highly inbred clone derived from seven generations of self-pollination of the wild diploid potato relative Solanum chacoense. We evaluated the F2 population for tuber size, shape and eye depth; skin and flesh colors; and dry matter content. Phenotypic segregation in this F2 population is astonishing. This single cross displayed a range of tuber traits approaching the entire diversity of potato landraces. Morphological characterization of potato used to classify accessions in genebanks is not representative of underlying genetic diversity. This is in agreement with other studies that have shown a lack of correlation between morphological/taxonomic classification and neutral genetic diversity, and a lack of correlation between either morphology or neutral genetic diversity and functional, trait-related genetic diversity in several species. We need better strategies for combining phenotypic and genetic characterization of accessions to develop predictive models that plant breeders can use to identify promising accessions for traits of interest.

Because of their adaptation to a diverse set of habitats and stresses, wild species of cultivated crops offer new sources of genetic diversity for germplasm improvement. Using an Infinium array representing a genome-wide set of 8303 single nucleotide polymorphisms (SNPs), phylogenetic relationships and allelic diversity were evaluated within a diversity panel of germplasm from sect. . This panel consists of 74 plant introductions (PIs) representing 25 species and provides a diverse representation of tuber-bearing germplasm. Unlike other molecular markers, genome-wide SNPs have not been widely implemented in potato. To determine relatedness between current species classifications and SNP-based genetic distances, a phylogeny was generated based on random individuals from each core collection PI. With few exceptions, SNP-based estimates of species relationships revealed general agreement with the existing taxonomic grouping of species in sect. . Genotype comparisons between the sect. diversity panel and a panel of 213 tetraploid cultivars and breeding lines indicated a greater extent of diversity between populations of native Andean landraces than among modern cultivated varieties. Comparison of SNP allele frequencies between the sect. panel and tetraploid cultivars identified loci with extreme divergence between cultivated potato and its tuber-bearing relatives. Several of these loci are associated with genes related to carbohydrate metabolism and tuber development, suggesting potential roles in potato domestication. The Infinium SNP data offer a new taxonomic view of potato germplasm, while further identifying candidate alleles likely to differentiate wild germplasm and cultivated potato, possibly underlying key agronomic traits.

Knowledge about the genetic diversity and structure of crop cultivars can help make better conservation decisions, and guide crop improvement efforts. Diversity analysis using microsatellite markers was performed to assess the level of genetic diversity in sweet potato in Uganda, and evaluate the genetic relationship between the Uganda’s germplasm and some genotypes obtained from Kenya, Tanzania, Ghana, Brazil and Peru. A total of 260 sweet potato cultivars were characterized using 93 microsatellite loci. The Ugandan collection showed a large number of distinct landraces, and very low (3 %) levels of genetic diversity between genotypes obtained from the different agro-ecological zones. There was low (6 %) levels of genetic diversity observed between the East African genotypes; however unique alleles were present in collections from the various sources. Pairwise comparisons of genetic differentiation indicated that Uganda’s germplasm was significantly different (P < 0.001) from cultivars from Tanzania, Ghana, Brazil and Peru. The presence of unique alleles in populations from various Uganda’s agro-ecological zones and other global regions, as well as the regional diversity patterns, suggest that efforts should be made to further collect and characterize the germplasm in more depth.

A. del Rio et al., 'Microsatellite (SSR) marker analysis to examine the effects of pesticide contamination on the genetic diversity of potato species', American Journal of Potato Research, pp.35-36, 2015 | Many natural habitats concur in close proximity to cultivated fields and thus native plant species have an increased risk of indirect pesticide contamination. In recent years the USPG initiated an investigation to test the effects of agrichemicals on reproductive traits of diverse potato species. We found that the pesticide carbofuran is capable of reducing duration of flowering and pollen viability. These results suggested the possibility that negative changes in these traits could limit reproductive ability non-randomly and cause genetic drift. SSR markers were used to evaluate that possibility by assessing the genetic structure of progenies originated from potato populations exposed to two levels of carbofuran. Eight populations of 5 species (acl, buk, hcr, med and rap) were used in this study. An untreated, uncontaminated population was also included as control. The results revealed that most of the SSR frequencies assessed did not differ significantly between control and pesticide-contaminated progenies. However, a few SSRs showed significant frequency shift and it impacted genetic diversity levels in some species; specifically buk and med. Therefore, these studies reveal that pesticides near wild species populations not only reduce reproduction in general, but also may specifically change population genetics in a way that reduces diversity

The genetic diversity among Indian strains of Ralstonia solanacearum, causal agent of bacterial wilt of potato, was assessed by repetitive sequence-based polymerase chain reaction (rep- PCR) method. Sixty three strains of R. solanacearum isolated from potato, which were collected from different states of India viz. Uttarakhand, Meghalaya, West Bengal, Himachal Pradesh, Orissa, and Karnataka under different agro-climatic regions. Characterization of races and biovars of these strains of R. solanacearum was done and two races (race 1 and race 3) and four biovars (bv 1, bv 2, bv2T and bv3) were recorded from potato. Genetic diversity these 63 strains of R. solanacearum was done by using rep-PCR (BOX, ERIC and REP- PCR primers). The strains of R. solanacearum formed 42 clusters (group) at 70% similarity coefficient. The strains of R. solanacearum isolated from Uttarakhand formed group 1- 5, 8-9 and group 23, from Meghalaya formed groups 6-7, 10-20, 24, 38-39, from West Bengal formed groups 25 and 27, from Odisha formed groups 26, 35- 37 and 40- 42, from Karnataka formed groups 22, 30-34 and from Himachal Pradesh formed group 21, 28-29. Maximum genetic diversity in strains of R. solanacearum was found, which were collected from Shilong (Meghalaya) and clustered in 18 clusters followed by strains collected from Nainital, hill areas (Uttarakhand) divided into 8 groups. However, the strains collected from plains i.e. Karanataka belongs to R1/bv3 cluster in one group, likewise the strains of Odisha R3/bv2 & 2T clustered in separate group and strains from West Bengal R1/bv3 clustered in one group. Thus the study indicated the existence of wide range of genetic diversity among the Indian strains of R. solanacearum causing brown rot of potato.

Principal component analysis was undertaken to estimate variability in 32 potato genotypes. Fourteen principal components accounted for 99.97 per cent variation. The genotypes were grouped into 5 non over-lapping clusters. The maximum intra cluster distance was found in cluster II (3.565) and minimum in cluster III and I (2.531). In general, the clustering pattern was not corresponding to their pedigree. The maximum inter cluster distance of 5.063 was found between clusters I and II, whereas minimum distance 4.213 was found between clusters III and IV. Cluster number III had maximum number of genotypes (08) followed by cluster number V (07), I and IV (5)and II (3). The genotype having maximum inter cluster distance showed maximum diversity, and thus they can be used in hybridization programme.

Understanding what farmers need in potato varieties and assessing available genetic resources at the farmer and district levels is important for the conservation and improvement of potato in Ethiopia. A survey was conducted in six major potato growing districts representing different agro-ecologies, cropping systems, market outlets, and levels of new variety adoption. Seventy to ninety percent of the farmers surveyed reported growing two or more potato varieties; some farmers reported growing up to five. The greatest diversity at the district level (up to 10 potato varieties) was recorded at Gumer & Geta where there is better access to new varieties while the lowest diversity was reported in districts with low access to new cultivars. The distribution of varieties differed among agro-ecologies as did the traits that farmers were most concerned with, such as drought tolerance, late blight resistance, yield potential, marketability, food value, storage quality, adaptation to low soil fertility, time to maturity and suitability for multiple harvesting. Farmers’ decision-making processes and external factors that influence potato variety diversity were also documented. The registration of predominant local varieties and use of these local varieties as a starting point for the development of improved varieties are some of the recommendations for future potato breeding in Ethiopia. Moreover, it is necessary to consider variations in agro-ecologies, cropping systems and market outlets in the process of developing varieties suitable for farmers’ and consumers’ real needs.

Understanding what farmers need in potato varieties and assessing available genetic resources at the farmer and district levels is important for the conservation and improvement of potato in Ethiopia. A survey was conducted in six major potato growing districts representing different agro-ecologies, cropping systems, market outlets, and levels of new variety adoption. Seventy to ninety percent of the farmers surveyed reported growing two or more potato varieties; some farmers reported growing up to five. The greatest diversity at the district level (up to 10 potato varieties) was recorded at Gumer & Geta where there is better access to new varieties while the lowest diversity was reported in districts with low access to new cultivars. The distribution of varieties differed among agro-ecologies as did the traits that farmers were most concerned with, such as drought tolerance, late blight resistance, yield potential, marketability, food value, storage quality, adaptation to low soil fertility, time to maturity and suitability for multiple harvesting. Farmers’ decision-making processes and external factors that influence potato variety diversity were also documented. The registration of predominant local varieties and use of these local varieties as a starting point for the development of improved varieties are some of the recommendations for future potato breeding in Ethiopia. Moreover, it is necessary to consider variations in agro-ecologies, cropping systems and market outlets in the process of developing varieties suitable for farmers’ and consumers’ real needs.

Understanding the nature and magnitude of genetic diversity and interrelationship among sweet potato genotypes for traits of economic importance is vital to effective crop improvement. Genetic variability, character association, path coefficient, and genetic diversity analysis for 17 qualitative and quantitative traits in 20 diverse sweet potato genotypes was undertaken. A wide range of genetic variation occurred for tuber yield per plant, carotene content, starch content, fresh weight of tubers per plant, and numbers of branch per plant. Fresh weight of tuber per plant had a positive phenotypic correlation with number of tubers per plant followed by days to maturity and vine internode length. Total carotene content had a positive significant association with vine length, number of leaves per plant, and number of branches per plant. Days to maturity had a positive phenotypic correlation with vine length, vine internode length, and number of leaves per plant. At the genotypic level the highest, positive, direct effect on fresh weight of tubers per plant was due to dry matter content and days to maturity followed by moisture content via numbers of tubers per plant and total sugar content. Cluster analysis divided genotypes into two main groups, indicating a genetic relationship among accessions. The genetic variability and traits relationship could provide new avenues to breed improved sweet potato.