T-type chloroplast DNA inSolarium tuberosum L. ssp.tuberosum was conferred from some populations ofS. tarijense Hawkes

The highly heterozygous and tetraploid nature of potato (Solanum tuberosum L. ssp.tuberosum) has hampered discovery of its wild ancestral species. Chloroplast DNA is a very reliable indicator to trace maternal ancestry of crops. Most of the common potato (grown worldwide) has unique, T-type chloroplast DNA derived from Chilean cultivated potato (both areS. tuberosum ssp.tuberosum). Analyzing seven different chloroplast DNA markers, I found all the T-type accessions of cultivated potatoes shared the same chloroplast DNA haplotype only with some accessions ofS. tarijense Hawkes and its derived hybrids. Thus, I conclude that some populations ofS. tarijense acted as the maternal ancestor of potato.     

Evolutionary pathway of T-type Chloroplast DNA in potato

Potato was domesticated in the Andes of South America. However, the presently worldwide-grown potato (Solanum tuberosum L. ssp.tuberosum, 2n=4x=48) has characteristic T-type chloroplast DNA that was introduced after late blight epidemics in the mid-19th century from the Chilean potato (2n=4x=48) grown in the southern coastal regions in Chile. Among many wild potato species, the same chloroplast DNA was found only in some populations of a diploid speciesS. tarijense Hawkes (2n=2x=24), which ranges from central Bolivia to northwest Argentina. To elucidate an evolutionary pathway of T-type chloroplast DNA fromS. tarijense to Chilean potato, 215 accessions ofS. stenotomum Juz. et Buk., considered to be the most primitive, diploid cultivated potato species, from which all the Andean cultivated species evolved, and 286 accessions of the most widely grown, Andean tetraploid cultivated speciesS. tuberosum L. ssp.andigena Hawkes (2n=4x=48) were examined in this study. No accession ofS. stenotomum had T-type chloroplast DNA, while nine accessions, mostly from northwest Argentina, ofS. tuberosum ssp.andigena had T-type chloroplast DNA. Therefore, I conclude that some populations ofS. tarijense having T-type chloroplast DNA were naturally crossed as female withS. tuberosum ssp.andigena from which the Chilean potato was selected.     

Characterization ofSolanum tuberosum simple sequence repeats and application to potato culiwar identification

With the continued introduction of new potato cultivars, accurate identification is becoming difficult but is essential for maintaining cultivar integrity and Plant Breeders’ Rights. Hypervariable DNA sequences, referred to as simple sequence repeats (SSRs) or microsatellites, have been reported to be an excellent source of genetic markers. To determine the abundance, distribution, and composition of SSRs withinSolanium tuberosum, 252 sequences were searched for tetranucleotide and smaller SSRs with a minimum length of 20 nucleotides and a maximum discrepancy of two nucleotides. In total, 40 unique SSRs were observed in the 252S. tuberosum sequences examined and occurred at a frequency of one SSR every 8.1 kb. To assess the ability of site-specific amplified SSRs to identify potato cultivars, a simple (TCAC)_m and compound (TCAC)_m ? (CTT)_n SSR 5’ to the starch synthase gene and a compound (C)_p ? (CT)_q ? (AT)_r ? (G)_s SSR 5’ to the sequence encoding mature proteinase inhibitor I, were examined and shown to produce unique DNA profiles for 73 of 95 tetraploid cultivars. In total, 24 alleles were observed at these loci and the accurately sized amplified DNA products can be used to establish a database for cultivar identification. Site-specific amplified alleles were somatically stable and have been conserved in clonal variants of Russet Burbank independently maintained for almost seven decades, a characteristic essential for cultivar identification. As genetic markers, the abundant, informative, and easily examined site-specific amplified alleles of SSRs are ideal for quickly and accurately determining cultivar identity of S.tuberosum ssp.tuberosum.     

Distribution of the 241 bp deletion of chloroplast DNA in wild potato species

The common potato (Solanum tuberosum L. ssp.tuberosum) has T-type chloroplast DNA characterized by a 241 bp deletion. To explore the maternal ancestry of the common potato, a total of 566 accessions of 35 wild species, collected mostly from central Bolivia to northern Argentina, were determined for presence or absence of the deletion by a simple PCR assay using primers flanking the deleted region of chloroplast DNA. Sixteen out of 80 accessions ofS. tarijense, S. berthaultii, andS. neorossii showed a shorter PCR amplified fragment. Sequencing of these fragments revealed that the same 241 bp was deleted at the same position in these accessions. This strongly suggests that the deletion event had occurred in wild species.     

Crossability of some green-peach-aphid-resistant tuber-bearing solanums,potential bridging species,andSolanum tuberosum ssptuberosum

Blue light fluorescence microscopy was found to be a quick and easy procedure for assessing pollen tube development in interspecific pollinations ofSolanum. Based on penetration of pollen tubes to the base of the style, several combinations of green-peach-aphid-resistant species and potential bridging species to S.tuberosum ssp.tuberosum should be considered for embryo culture. Sterile or highly infertile hybrids were obtained between green-peach-aphid-resistantS. tuquerrense andS. tuberosum ssp.tuberosum and are described. Slightly fertile hybrids were obtained betweenS. tuquerrense andS. polytrichon, a species compatible withS. tuberosum ssp.tuberosum.     

Exploitation of Exotic, Cultivated Solanum Germplasm for Breeding and Commercial Purposes

Native potato species (NPS) are cultivated potatoes which do not belong to S. tuberosum ssp. tuberosum. They are maintained by the farmers of the Andes for subsistence under harsh environmental conditions where other potatoes cannot compete. Within the huge phenotypic variability between and within these species certain accessions possess resistances to different pests and diseases, remarkable culinary and processing quality and favourable nutritional properties. We present first evaluation results of a set of NPS for these characters and discuss prospects for exploiting this valuable germplasm for breeding and for developing novel products for niche markets.     

Inheritance of the resistance toGlobodera rostochiensis pathotype Ro2 in potato

Nine advanced tetraploid potato clones withS. tuberosum ssp.tuberosum, S. tuberosum ssp.andigena, andS. vernei background were found to be highly resistant toGlobodera rostochiensis pathotype Ro2. In order to characterize the inheritance of the resistance to Ro2 and determine the genotype of these Ro2-resistant clones, a series of testcrosses to susceptibleS. tuberosum cultivars, as well as crosses between the resistant clones, were made. A total of 1081 seedlings corresponding to 18 families were grown, inoculated with 3000G. rostochiensis juveniles (J2), and evaluated by the root-ball method. To determine which genetic model best fit the data, goodness-of-fit-tests were performed. The analysis assumed tetrasomic inheritance under the hypothesis that resistance is due to one locus with complete dominance. From the analysis of the data it is concluded that there is no consistent evidence against the hypothesis that a single dominant gene is associated with the resistance to Ro2 and that the Ro2-resistant clones are simplex. In general, the number of cysts observed on the root balls was low compared with the results of other studies, the results of the different inoculations were variable, and there was an excess of resistant plants. Possible explanations for these observations are discussed.     

Characterization of forty-four potato varieties for resistance to common scab,black scurf and silver scurf

Common scab, black scurf and silver scurf belong to serious diseases of cultivated potato that especially impair tuber quality. Tuber infection in 44 potato (Solanum tuberosum ssp. tuberosum L.) varieties was evaluated using two measures – severity and incidence of infected tubers. Both measures were highly correlated. An important result derived from this study supports fungicide application against potato late blight secondarily acts on reducing tuber infection by all evaluated pathogens. Therefore, the conventional potato growing seems to be more effective compared to ecological growing. The pedigree analysis of 44 varieties indicated the presence of Solanum demissum genotypes in the variety genome may negatively affect variety response to Helminthosporium solani presence.     

Reaction of some wild and cultivated potato varieties to charcoal rot

With a view to select potato varieties possessing resistance to charcoal rot, laboratory tests were carried out at the Central Potato Research Institute, Simla (India). Five hundred and twenty six clones comprising tuber-bearing species ofSolanum and varieties and hybrids of potato were screened for their reaction toMacrophomina phaseoli (Maubl.) Ashby. A high degree of resistance was observed in six clones ofSolanum chacoense and four hybrids withS. chacoense germ plasm, while moderate susceptibility was observed in another six clones ofS. chacoense, three clones ofSolanum tuberosum ssp.andigena and nineteen hybrids produced at the Institute.     

Potato cultivars: Genetic variation within putative clones

Four of five major cultivars of the potato (Solanum tuberosum L. ssp.tuberosum) from different sources were found to vary genetically. This variability was detected by an electrophoretic study of enzymatic activity for alkaline phosphatase and glucosephosphate isomerase. An examination of red cultivars from Beltsville, Md. suggests that the apparent intracultivar variability observed for Red Pontiac may be due to cultivar mislabeling rather than mutation or mitotic recombination. The results of this study raise concerns about potato cultivar certification and interpretations of some of the previous cultivar work. We suggest that a more extensive survey of intracultivar variability be carried out. Further, we suggest that these genetic markers and others could be used in cultivar identification.     

Pollen-pistil incompatibility in a diploid hybrid potato population with cultivated and wild germplasm

The basis of low seed set was investigated in a diploid hybrid population with germplasm from the cultivated speciesSolanum tuberosum spp.tuberosum andS. tuberosum ssp.phureja and the wild speciesS. chacoense. Controlled crosses were performed following an incomplete diallel mating design which included the hybrid population and the parental species. Pollen grain germination and pollen tube growth were observed with fluorescence microscopy in 174 intrapopulation and interspecific combinations of genotypes. Fifty percent of the combinations of genotypes within the hybrid population and 46% of those between this population and the parental species were incompatible; overall, 71% of the interspecific combinations of genotypes were compatible when plants of the hybrid population were used as females, vs. 5% when used as males. Although the site of reaction could vary in a given intrapopulation or interspecific cross with the combinations of genotypes, pollen tube inhibition occurred in the first third of the style in 42% of them. Since the gene pool of the hybrid population had been widened with germplasm from other geographic areas and the genotypes ofS. tuberosum ssp.tuberosum, S. chacoense andS. tuberosum ssp.phureja used in this study were not the ones involved in the original crosses, it is concluded that the S-locus is not controlling the incompatibility reaction but rather that a cross-incompatibility system, possibly governed by more than one locus, is acting.     

Potato (Solanum spp.) in the hot tropics. VI. Plant population effects on soil temperature,plant development and tuber yield

Nine experiments were run at three hot tropical sites (5–12°S, 180–800 m) within Peru to quantify the influence of plant population on soil temperature and growth and yield of the potato.Radiation interception was greatest at the highest plant populations and soil cooling was directly proportional to the amount of crop cover over the soil, but no appreciable effect on the timing of tuber initiation was apparent. More stems per unit land area leading to a higher leaf area index (lai) were primarily responsible for greater interception of radiation at the higher plant populations, although some compensation in stem number per unit land area and in lai at lower populations was evident later in the season.In general, tuber yield increased linearly with increases in planted population over the range studied (2.7–12.5 plants m⁻², and in one experiment to 31.7 plants m⁻²), and was proportional to increases in the amount of intercepted radiation. Tuber yields ranged from 8 to 60 t ha⁻¹ over sites and populations. Vigorous clones with Solanum tuberosum spp. andigena in their genetic background constituted the exceptions to this linear trend, and for these clones yields declined at the highest populations, particularly when the rectangularity of planting vastly deviated from square patterns. Tuber yield of Solanum tuberosum spp. tuberosum and Neotuberosum (S. tuberosum spp. andigena selected for tuberization under long-day conditions) clones did not respond to variations in rectangularity of planting and, probably due to their small stature and early maturity, did not demonstrate signs of intense between-plant competition for tuber yield as measured with the Kira competition density index. In contrast, for clones with Solanum tuberosum ssp. andigena in their genetic background, maximum tuber yield at populations greater than 5.5 plants m⁻² was dependent on the rectangularity of planting, and declined as the latter deviated from squareness.Since the proportion of marketable tubers was scarcely affected by the planting densities, plant population of S. tuberosum ssp. tuberosum clones planted in hot climates should be as close as possible without limiting the amount of soil available for hilling-up.     

Rosa: A new golden nematode resistant variety for chipping and tablestock

Rosa is a golden nematode resistant variety with chipping potential comparable to Norchip and with good cooking quality. It is resistant to early blight and leaf roll, and moderately resistant to late blight. Rosa is a hybrid between North AmericanSolarium tuberosum ssp. and South AmericanS. tuberosum ssp.Andigena clones.     

Use of reciprocal grafts to elucidate mode of resistance to Colorado potato beetle (Leptinotarsa decemlineata (Say)) and potato aphid (Macrosiphum euphorbiae (Thomas)) in six wildSolanum species

Reciprocal grafts were done between potato (Solanum tuberosum) and six wildSolanum species known to be resistant to the Colorado potato beetle (Leptinotarsa decemlineata (Say)). Potato or wildSolanum foliage from each reciprocal graft was fed to first instar beetles or adult potato aphids (Macrosiphum euphorbiae (Thomas)). The proportion of second instar larvae after 48 h and survival and fecundity (number of nymphs per female) of the aphids were used to i estimate the resistance level of the foliage. Survival and fecundity of potato aphid were reduced on wildSolanum foliage (except withS. circaeifolium ssp.capsicibaccatum andS. okadae) used as scion or rootstock, but were not different from the control (potato-potato graft) on potato foliage. Development of Colorado potato beetle onSolanum foliage was reduced. In some cases, potato foliage grafted to wildSolanum became resistant to the beetle. Results suggest that a chemical factor or factors providing resistance to Colorado potato beetle are translocated from foliage of some wildSolanum species to potato foliage. They also indicate that mode of resistance to the two insects differs quantitatively or qualitatively.     

Polygene mapping as a tool to study the physiology of potato tuberization and dormancy

Efforts to breed for the ability to tuberize under long days or for the length of tuber dormancy should benefit not only from information on the location of genes associated with these traits, but also from an understanding of the hormones the genes control. Understanding the role of the respective genes is a logical step in developing the best breeding strategy, both for conventional breeding and for gene transfer using molecular techniques. Polygene mapping affords a way to achieve such understanding and is also a tool to study the physiology of potato tuberization and potato tuber dormancy. The addition of DNA markers to a plant population facilitates the mapping of polygenes that control quantitatively inherited traits segregating in the population. A quantitative trait locus denotes a region of chromosome that is linked to the marker gene and which has a significant effect on the quantitative trait under study. Our approach has been to find the quantitative trait loci associated with tuberization and tuber dormancy in a segregating diploid population, and then to map the population for quantitative trait loci associated with levels of hormones implicated in the control of these two traits. We are using a population derived from a hybrid between haploidSolanum tuberosum andS. berthaultii that was backcrossed to a different haploidS. tuberosum. We have found ten quantitative trait loci for the ability to tuberize under long days and eight quantitative trait loci for tuber dormancy. In the same population we have found one or more quantitative trait loci for polyamines, abscisic acid, tuberonic acid, tuberonic acid glucoside, zeatin riboside, and gibberellin A₁. Some of the hormone quantitative trait loci have coincided with quantitative trait loci for tuberization or dormancy. Implications of such commonality are discussed, along with the usefulness and limitations of the methods.     

ND2858-1: A useful source of resistance to the Colorado potato beetle

This paper describes a new source of host-plant resistance to the Colorado Potato Beetle (CPB;Leptinotarsa decemlineata (Say)) in a tetraploid potato (Solanum tuberosum L.) selection, ND2858-1. This hybrid was recorded as a cross betweenS. fendleri ssp.fendleri (A. Gray) and NDSU selection ND1215-1. Field defoliation of this and progeny clones from a subsequent cross to an cultivar was reduced by 50% to 90% in open-choice field screening plots. Progeny of ND2858-1 are vigorous, with high yield potential, and some clones have tuber glycoalkaloid content equivalent to commercial cultivars. These clones are male and female fertile and may be useful to other potato breeding programs. Further characterization of this resistance source is in progress.     

Introgression and stabilization oferwinia tuber soft rot resistance into potato after somatic hybridization ofsolanum tuberosum ands. brevidens

Resistance to potato tuber soft rot caused byErwinia carotovora was transferred fromSolanum brevidens to the cultivated potato over the course of four backcross generations originating from a somatic hybrid. Soft rot reactions were determined via a tuber plug inoculation method developed during the course of these experiments. Soft rot resistance was highest in the somatic hybrid (only ca. 20% of tubers and plugs showed evidence of severe rotting) and lowest among progeny of control potato x potato crosses (ca. 80% of tuber plugs showed severe rot). Backcross generations involving somatic hybrids were intermediate in their reaction, and resistance stabilized to about 60% of tuber plugs showing severe rot in the BC₂ through the BC₄. Reciprocal crosses showed no difference in the inheritance of soft rot resistance, indicating that neitherS. brevidens norS. tuberosum donor cytoplasm had a significant effect on the expression of resistance. Crosses between BC₃ siblings where noS. brevidens genetic markers were detected but resistance was segregating demonstrated a dosage effect for soft rot resistance. We conclude that introgression of soft rot resistance has occurred and that at least one locus responsible for resistance inS. brevidens now resides in theS. tuberosum genome.     

Male sterility and 2n pollen in 4x progenies derived from 4x×2x and 4x×4x crosses in potatoes

Summary The objectives of these experiments were to evaluate male sterility (MS) and 2n pollen frequency in 77 4x×2x families and 26 4x×4x families. The 2x parents were haploid-species hybrids and the 4x parents mainly clones withS. tuberosum ssp.tuberosum (tbr) andS. tuberosum ssp.andigena (adg) in their genetic background. The female parents had different cytoplasms: adg, tbr,S. demissum (dms), andS. stoloniferum (sto). Families from female parents with adg or dms cytoplasm did not have MS plants. However, families derived from crosses of many tbr females with 2x hybrids and a 4x adg clone had a high percentage of MS plants; all the progenies from cv. Serrana (sto cytoplasm) possessed tetrad sterility. These results can be explained as due to an interaction between a dominant male sterility (Ms) gene with tbr and sto cytoplasms. Some MS 4x hybrids (tbr×adg) used as females had the Ms gene, but male fertility was restored in some plants of their progenies when they were crossed with 4x tbr clones. This indicates that some tbr clones have a fertility restorer gene (Rt). The results from both 4x×2x and 4x×4x families fit the expected ratios assuming chromatid segregation for both the Ms and Rt loci. The gene frequency of parallel spindles was estimated in the 4x population as 0.74.     

Analyzing genotype by environment interaction in potato using yield-stability index

The plant breeding program of the National University of Colombia carried out 10 potato regional trials during 1998 and 1999 to evaluate 15 promising potato clones (Solanum tuberosum ssp.andigena). Genotype by environment interaction was analyzed using Kang’s methodology, which links yield performance and phenotypic stability. A MACRO was implemented using the SAS system to obtain yield-stability indices. Shukla’s variance was estimated by restricted maximum likelihood (REML), which allowed handling unbalanced data for both genotypes and replicates. In addition, a multivariate analysis methodology was developed, based on the yield-stability index. This methodology is useful when tuber yield is categorized by size and quality, which is usual in Colombian potato harvests.     

Cytoplasmic substitution inSolanum. I. Seed production,germination, and sterilities of reciprocal backcross generations

Summary Genes ofSolanum tuberosum L. ssp.tuberosum were introduced into cytoplasm ofS. tuberosum ssp.andigena (Juz. & Buk.) Hawkes andS. phureja Juz. & Buk. to reduce cytoplasmic sterilities. Alleles that influenced berry set and seed content produced differences between reciprocal progenies. Their expressions were interpreted in terms of genes of the maternal and/or paternal parents. When the ssp.andigena genotype was introduced from the maternal parent if favoured high berry set and low seed number. Maternal ssp.tuberosum favoured lower berry set and higher seed number. The source ofS. phureja cytoplasm, aS. phureja×S. chacoense F₁, used as maternal parent favoured lower berry and seed set. During successive backcrosses progeny expressions approached those of the recurrent ssp.tuberosum pollen parents. A low level of pollen sterility occurred in BC₂ plants, unrelated to direction of cross or cytoplasmic factors. By BC₄, seed set and fertility were as good as ssp.tuberosum, and recurrent backcrossing could be terminated without loss of seed production or fertility. Pennsylvania Agricultural Experiment Station Journal Series No. 7493.