Use of seedling progeny tests for genetical studies as part of a potato (Solanum tuberosum subsp. tuberosum) breeding programme

A diallel set of crosses, including selfs and some reciprocal crosses, was made between 15 parents chosen for their male fertility from those included in a tetraploid potato (Solanum tuberosum subsp. tuberosum) breeding programme at the Scottish Crop Research Institute. Seedling progeny tests were used to evaluate the progenies for non-race-specific resistance to late blight (Phytophthora infestans) in both foliage and tubers, quantitative resistance to the white potato cystnematode (PCN) (Globodera pallida) and the commercial worth of their tubers as judged by breeders' visual preference. No reciprocal differences were found. Comparisons of the selfs and crosses revealed inbreeding depression for breeders' preference, which varied among the parents from negligible to severe, whilst there were also statistically significant differences for foliage and tuber blight, but not for PCN. When the selfs were omitted from the combining ability analyses, large differences in general combining ability (GCA) were found for all four traits, and smaller differences in specific combining ability for tuber blight and breeders' preference. The only statistically significant correlation between GCAs for different traits was a favourable one of r = 0.56 between foliage and tuber resistance to late blight. It was concluded that prospects were good for simultaneously improving all four traits by multitrait genotypic recurrent selection.     

QTL mapping of yield, agronomic and quality traits in tetraploid potato (Solanum tuberosum subsp. tuberosum)

Interval mapping of quantitative trait loci (QTL) for 16 yield, agronomic and quality traits in potato was performed on a tetraploid full-sib family comprising 227 clones from a cross between processing clone 12601ab1 and table cultivar Stirling. Thirty-eight AFLP primer combinations and six SSRs provided 514 informative markers which formed a molecular marker map comprising 12 linkage groups (LGs) in 12601ab1 (nine with four homologous chromosomes) which were aligned with 12 in Stirling (11 with four homologous chromosomes), with four partial groups remaining in 12601ab1. Two LGs were identified unequivocally as chromosomes IV and V and eight others were tentatively assigned with chromosomes VII and X unidentified. All of the traits scored had moderately high heritabilities with 54–92% of the variation in clone means over 3 years and two replicates being due to genetic differences. A total of 39 QTLs were identified. A QTL for maturity was identified on chromosome V which explained 56% of the phenotypic variance, whereas the other QTLs individually explained between 5.4 and 16.5%. However, six QTLs were detected for after-cooking blackening and four for each of regularity of tuber shape, fry colour both after storage at 4 and 10°C and sprouting. Just two QTLs were found for each of yield, the two ‘overall’ scores, crop emergence, tuber size and common scab and just one QTL was detected for each of dry matter content, keeping quality, growth cracks and internal condition. The implications for practical potato breeding and for practical linkage and QTL analysis in autotetraploids are discussed.     

Yield and cooking qualities of somaclonal variants of cv. Russet Burbank selected for resistance to common scab disease of potato

We previously obtained somaclonal variants of the important French fry processing cultivar Russet Burbank with significantly enhanced resistance to common scab disease. In this study we have shown the commercial merit of a proportion of these variants through comparison of relative yield and tuber quality with the parent cultivar Russet Burbank. Whilst we showed a weak negative correlation between tuber yield (as assessed by weight of tubers per plant) and relative disease resistance within selected variants, we identified several with equivalent yields to the parent cultivar. Furthermore, two disease-resistant variants (TC-RB8 and NZ-24B) consistently yielded more tuber mass than the parent. The majority of our Russet Burbank variants showed equivalent tuber quality characteristics (occurrence of defects, tuber specific gravity and dry matter content, and flesh colour) and cooking qualities (fry colour and presence of dark end defects) to the parent cultivar. Independent testing by a commercial French fry processor confirmed these quality characteristics. We present data demonstrating that highly common scab disease-resistant somaclonal variants of Russet Burbank have commercially acceptable tuber yield and quality characteristics, comparable to the industry standard and parent Russet Burbank cultivar. We also demonstrate the value of in vitro cell selection techniques for potato cultivar improvement.     

Assessment of five cultivars of potato (Solatium tuberosum L.) in a competition diallel

In 1992 and 1993, potato cultivars Cara, Estima, Pentland Dell, Pentland Javelin and Torridon were assessed in all possible pairings in three consecutive drills, such that one member of the pair (the cultivar) was the centre-drill, and the other member (the neighbour) was in the two adjacent drills. Each year the trial was a randomised complete block design with four replicates. Inter-cultivar competition was present for height, total tuber yield, ware yield and dry matter content, but not for emergence and maturity. Cultivar heights and dry matter contents under inter-cultivar competition and in pure-stands were highly correlated, whereas for total and ware yields, the rankings of cultivars in pure-stands were different from those under competition. Pure-stand yields were predicted for the two years separately because of year × cultivar and year × neighbour interactions. When the average total yield of the outer-drills was used as a covariate to adjust centre-drill yields to pure-stands, predicted yields were closer to those observed than were yields under competition, but there was little improvement in the correlations. In contrast, not only were the predicted values even closer to the observed ones when based on individual neighbour effects, the correlations were much higher (r = 0.76–0.94). Unfortunately, in plant breeding trials with large numbers of entries, precise estimation of individual neighbour effects would require an unrealistically large number of replicates. Hence, for the final stages of yield assessment of new cultivars, it is still desirable to use multiple-drill plots and to discard the outside drills where inter-cultivar competition can occur.     

Early-generation selection between and within pair crosses in a potato (Solanum tuberosum subsp. tuberosum) breeding programme

 In 1992, 72 seedlings from each of 198 pair crosses were grown in a glasshouse, and the tubers produced by each plant were visually assessed on a 1–9 scale of increasing preference. Three groups of four progenies with high, medium and low mean scores were chosen to progress, without selection via tuber progenies and four-plant plots at a high-grade seed site, to replicated yield trials in the third clonal generation. The three groups maintained their high, medium and low scores for visual preference over the three clonal generations and also had high, medium and low scores in the second and third clonal generations for yield, size and appearance of tubers, all of which were components of visual preference. The three groups were predicted to have 13.6%, 1.8% and 0.2% of their clones exceeding the mean of 13 control cultivars for visual preference in the replicated trials, and 12.1%, 4.9% and 1.4% for yield, and 56.8%, 37.1% and 14.8% for appearance. The experiment confirmed that selection for visual preference within crosses in the seedling and first clonal generations is very ineffective, but that worthwhile progress can be made from selection in the second clonal generation, with correlated responses for faster emergence, earlier maturity, higher yield and greater regularity of shape (appearance). Combining selection of the high group of progenies with selection in the second clonal generation of the best 34 out of the 120 clones in this group, produced a response in visual preference in the third clonal generation of 1.00 compared with a maximum possible of 1.74. Ways of achieving further improvements in early-generation selection are discussed. Received: 26 May 1998 / Accepted: 9 June 1998     

Simulation of fertilizer influence on yield and quality of potato (Solanum tuberosum) tubers by nonlinear optimization method

Data of yield characteristics and the main chemical compounds of potato tubers, received from special NPK-fertilized pot and field trials, were individually evaluated by multiple regression analysis. The best suited mathematical functions, including linear, quadratic and interactive terms of N-, P- and K-concentrations in tuber dry matter, were integrated as independent variables into the models and the SUMT-method was applied for the nonlinear programming.Particular nutrient requirements could be derived from different NPK-ratios which were obtained by optimization. These ratios led to maximum tuber yield (=objective function) while at the same time observing special threshold values (e.g. nitrate) or limiting indices (=constraints) of tuber quality. By means of simulation it was possible to demonstrate characteristic differences between the effect of N-fertilization and varied N-concentrations on tuber yield and composition.Calculation of dependent variables by fixed NPK-ratios of the tubers resulted in excellent correspondence of the values for several parameters with the predictions made by both models, which were based on pot or field experiments.     

Producing commercially attractive,uniform true potato seed progenies: the influence of breeding scheme and parental genotype

The production of attractive, uniform true potato seed (TPS) progenies was investigated. Four breeding schemes were compared: intercrossing tetraploid cultivars (cv x cv); doubled dihaploids x cultivars (ddh x cv); cultivars x diploid unreduced-gamete producers (cv x FDR) and doubled dihaploids x diploid unreduced-gamete producers (ddh x FDR). Fifty three progenies and five clones were grown in a glasshouse in a randomised complete block design with three replicates of 25 plants per progeny and clone. Each plant's tubers were counted and the colour, shape, quality of skin finish, flesh colour, and commencai attractiveness (which includes yield) recorded. The most uniform progenies were also selected by visual comparison with the clones. For mean attractiveness, differences (P < 0.001) between breeding schemes and between progenies within breeding schemes were detected. The cv x cv and cv x FDR progenies were more attractive than clonal controls. There were significant additive and non-additive effects for attractiveness in all breeding schemes except cv x FDR. There were between-progeny differences (P < 0.001) for uniformity for all characters. Progenies uniform for one character could be variable for other traits. Breeding schemes gave different levels of uniformity (P < 0.001) for all characters except shape and flesh colour, but none gave low levels of variation for all traits. Doubled-dihaploid parents increased the variation in progenies. There were uniformity differences (P < 0.001) between progenies within breeding schemes for all characters. Evidence of additive and nonadditive genetic variation for uniformity in all traits was detected. In each breeding scheme, parents with good general combining ability (GCA) for uniformity in several characters were identified. Visually selected uniform progenies had parents with good GCAs for uniformity in a range of traits and high specific combining abilities (SCAs) for several traits. A desynaptic first-division restitution (FDR) clone and a male-sterile doubled-dihaploid clone had the best GCAs for tuber uniformity in TPS progenies. Achieving multitrait uniformity in TPS is problematic but may be aided by the selection of parents with GCAs for uniformity coupled with progeny testing to allow for non-additive effects.     

An investigation into the relations between some growth parameters and yield of barley

Twenty-five field experiments on barley were done at four sites from 1970 to 1975, with an additional site in 1975, comparing five rates of nitrogen application. The crops were sampled at c. 14-day intervals from about the four-leaf stage to maturity to follow changes with time in the dry weights of the constituent plant parts and to measure fertile tiller number, grain number per ear and grain weight. Some data have been selected from this body of information and regression analysis has been used to assess the possible importance of pre- and post-anthesis growth in determining the yield of barley. Ear emergence was taken as an approximate indicator of anthesis. Yield was closely related (r=+0–96) and almost equal to the amount of dry matter accumulated before ear emergence for twenty-one of the experiments, with a regression coefficient of 0–95. In two of the remaining experiments the regression coefficient was greater, 1–14; and smaller in the other two, o-8i. Plant population is also shown to affect the regression coefficient. Despite these anomalies grain yield was more closely related to plant dry weight at ear emergence than to the increase in weight after ear emergence (r =+0–79). The increase in plant dry weight after ear emergence was frequently less than the yield of grain, suggesting that the plant can compensate for inadequate photosynthesis during grain filling. The result of this compensation is a reduction in straw dry weight. This implies that previously assimilated dry matter is transported to the grain, or that respiratory losses from the straw are not replaced by current photosynthesis. These observations suggest that yield may be limited by sink capacity rather than by photosynthesis after ear emergence. The main component of sink capacity, grain number per m² was closely related to yield (r =+0–95) and is known to be determined at or before anthesis. Grain size was shown to be related to grain number per ear (r= 4- 0–99), suggesting that grain size is also, at least partially, determined at ear emergence. Therefore, all the yield components are determined, wholly or partly before ear emergence.     

A cytogenetic and phenotypic characterization of somatic hybrid plants obtained after fusion of two different dihaploid clones of potato (Solatium tuberosum L.)

Summary Somatic hybrid plants of various ploidy levels obtained after chemical fusion between two dihaploid clones of potato Solanum tuberosum L. have been analysed by cytological, morphological and molecular methods. The hybrid nature of tetraploid and hexaploid plants and the genome dosage in hexaploid hybrids were confirmed by Giemsa C-banding. Tetraploid and hexaploid hybrids showed numerical as well as structural chromosome mutations. The latter occurred mainly in the nuclear organizing chromosome. The tetraploid hybrids were more vigorous than the dihaploid parents as demonstrated by an increase in height, enlargement of leaves, increase in the number of internodes, restored potential for flowering and increased tuber yield. The grouping of tetraploid somatic hybrids into various classes on the basis of leaf morphology revealed that plants with a full chromosome complement were more uniform than aneuploids. Many hexaploid somatic hybrids were also more vigorous than the dihaploid parents and could be grouped into two different classes on the basis of floral colour and tuber characteristics, the differences being due to their different dosage of parental genomes. Most of the tetraploid somatic hybrids showed pollen development halted at the tetrad stage as one of the parental clones contained a S. Stoloniferum cytoplasm. However, one tetraploid plant produced pollen grains with high viability. The chloroplast genome in the hybrid plants was determined by RFLP analysis. All of the hybrids had a cpDNA pattern identical to one parent, which contained either S. Tuberosum or S. Stoloniferum cpDNA. A slight preference for S. Tuberosum plastids were observed in hybrid plants. No correlation between pollen development and plastid type could be detected.     

An analysis of the effects of nutrient supply on the growth of potato crops

Fertilizer nitrogen did not delay tuber initiation by the potato variety King Edward in the field, but slowed the early growth of tubers. Later, N hastened tuber growth and the largest amounts prolonged it. Leaf and stem growth were increased by N from an early stage. Leaf area index (L) reached maxima of 2.5 to 3.0 with the largest amounts of N, and 1.0 with no nitrogen: L decreased after late July, faster with increased N, and only the largest amount prolonged the life of the haulm. N increased leaf area duration (D) by up to 125% in both years. D was 21% greater in 1964 than 1963, and net assimilation rate in August and September was larger; consequently mean yield was 50% more in 1964. Uptake of nitrogen and N % of dry matter were increased by increasing nitrogen. The N % of tuber dry weight remained constant or increased slightly from about 2 weeks after tuber formation, while N % of the leaves and stems decreased rapidly, and much N was transferred from tops to tubers. The 1964 results suggest that tuber growth depends on continued nitrogen uptake by the plant. P and K had small effects compared with those of N. K increased leaf area duration by 9% in 1963 and 3% in 1964, and yield by 11 and 8% respectively. P increased leaf area duration by 17% and yield by 9% in 1964. K had very small effects until the end of the season, when it prolonged the period of growth. P increased growth rates of all parts of the plant up to 4 weeks from emergence, and the differences in dry weight at that time persisted to maturity but did not increase.     

Influence of minisett sizes on dry matter accumulation and fresh tuber yield of white Guinea yam (Dioscorea rotundata)

Studies were conducted in 2005 and 2006 at Irrua, Nigeria, to determine the performance of various sizes of minisetts of Dioscorea rotundata cv. 'Obiaoturugo' evaluated for size and yield of yield matter and seed yams. These trials involved a macrosett (250 g) and six minisett sizes (25, 30, 35, 40, 45 and 50 g) in a randomised block design with four replicates. The results indicated that larger minisetts had higher degree of field establishment, foliation, leaf area index, total dry weight, percentage of leaf dry matter and net assimilation rate. These growth parameters influenced higher crop growth rate, which was responsible for higher fresh tuber yield. The macrosett's fresh tuber yield was the greatest (20.48 t ha⁻¹) but had the least multiplication ratio (8.19). The greatest multiplication ratio was obtained from 30-g setts.     

Genetic variation in Solanum tuberosum group Andigena haploids

Summary A random sample of haploids, derived from 28 parental introductions from Solarium tuberosum Gp. Andigena, was used to estimate the quantitative genetic variation for six traits within this group. The six traits analyzed on a plot mean basis were: total tuber weight, fresh vine weight, total fresh weight (tuber+vine), dry vine weight, total dry matter (tuber+vine) and specific gravity. Progenies were obtained following the North Carolina mating Design I and were evaluated along with the female parental clones at two locations. Components of variance and narrow sense heritabilities were calculated by two methods: Design I and female parent-offspring regression. Heritability estimates calculated by the two procedures were in close agreement for most traits. The estimates for total tuber weight from the Design I procedure were twice that from parent offspring regression. The genetic coefficient of variation for these traits indicated a large amount of total genetic variance in this population. Genetic variability for total tuber weight was mostly additive, while both additive and dominant genetic variances were equally important for the remaining traits.     

Effects of common scab (Streptomyces scabies) on potatoes

Seed tubers with severe (71% cover) or slight (12% cover) common scab selected from a badly infected crop of cv. Maris Piper were boxed for sprouting in November and February and planted in field experiments at Woburn and Rothamsted in 1980. The severely scabbed seed lost more moisture than the slightly scabbed seed during sprouting and sprouted from a larger number of eyes but total stem numbers were greater on plants from the slightly scabbed seed. Plant growth during the first 6–9 wk after planting was less from the severely scabbed than from the slightly scabbed seed. This was shown by records of ground cover, leaf area index, fresh weights of stems and leaves, total tuber yield (18% lower at 9 wk) and tuber number. Subsequently these differences became non-significant. Seed with slight scab boxed in November produced smaller numbers of progeny tubers than that boxed in February but there were no other consistent effects of boxing date on growth and yield. Scab incidence on progeny tubers was very slight and unrelated to the severity of disease on the seed tubers. It seems unlikely that severe scab infection of seed tubers would significantly decrease tuber yields except perhaps in early potato production.     

Genotypic influence on in vitro induction, dormancy length, advancing age and agronomical performance of potato microtubers (Solanum tuberosum L.)

Microtubers of 13 cultivars, largely grown in Italy and other European countries, were induced. They were stored in the dark at 3°C for different periods (28, 56, 84 and 105 days), prior to being transferred to 20°C for between 4 and 17 weeks. Following removal to room temperature, sprouting was recorded and dormancy duration quantified. Dormancy decreased from 28.1 to 19.9, 11.1 and 7.8 days with reduced time of storage. Cvs Arsy, Nicola and Jaerla took consistently more time for dormancy release. The dormancy duration was linearly and inversely correlated with the length of storage. After sprouting, tubers were held at 20°C for various intervals and a range of physiological ages (0, 368, 720 and 1008 degree days) were accumulated. The field comparison of microtubers evidenced a plant growth response and tuber yield/plant affected by the cultivar and physiological age. In early cultivars (Jaerla), a better performance was shown by younger tubers; the opposite trend was noted in Alpha (a later cultivar) with an increase in stems/plant, tubers/plant and tuber yield/plant for tubers with greater physiological age. Like conventional seed tubers, microtubers showed differences in optimum physiological age associated with cultivar earliness. This study has provided some indications on how to enhance emergence and haulm development of plants from microtubers.     

Inbreeding and true seed in tetrasomic potato. II. Selfing and sib-mating in heterogeneous hybrid populations of Solanum tuberosum

 Inbreeding depression may affect the performance of consecutive generations of potatoes propagated by true potato seed (TPS). The effect of inbreeding was established using selfed and sib-mated generations of five TPS families. Correlation coefficients were calculated between the level of inbreeding and different traits. Inbreeding depression was expressed mainly by pollen viability, as measured by its stainability (r=−0.912, P<0.01), and tuber yield (r=−0.837, 0.01<P<0.05). The results also indicated that without unavoidable selection inbreeding depression is expected to be more evident. Furthermore, the TPS families responded quite differently to inbreeding depression. They did not show the same amount of depression for yield as they did for the characters concerning fertility. The high tuber-yielding families displayed a greater inbreeding depression for tuber yield than the lower-yielding families. Received: 10 November 1997 / Accepted: 3 March 1998     

Growth, partitioning, and harvest index of tuber-bearing solanum genotypes grown in two contrasting peruvian environments

Ten Solanum potato genotypes, including four primitive species and six hybrids, were grown to maturity near 230 and 3273 meters in elevation at two sites, Coast and Sierra, in Peru. Growth data, with emphasis upon tubers and leaves, were collected periodically to analyze the plant components which differed in these contrasting environments. Nine of the Solanum species/cultivars effectively partitioned dry matter into tubers with values reaching 73 to 85% of the total plant at mature harvest in the Sierra but dropping to 33 to 75% on the Coast. These harvest index differences were, however, accompanied by no consistent changes in total leaf area, specific leaf area, nor number of tuber initiated. Consistent differences did occur in having shorter plants in the Sierra and an increased tuber dry matter percentage, 20 to 28%, in the Sierra compared to 14 to 21% on the Coast. Linear relationships exist between plant tuber harvest index versus tuber yield and versus total plant dry matter on both the Coast and in the Sierra.     

Optimal rates of 2,4‐dichlophenoxyacetic acid foliar application for control of common scab in potato

Applications of the synthetic auxin 2,4‐dichlorophenoxyacetic acid (2,4‐D) to the foliage of potato plants can reduce common scab, a tuber disease. However, in prior research effective applications at 200 mg L^?1 2,4‐D resulted in phytotoxic side effects with reduced tuber yield and quality. This study showed that minimal significant threshold rates from 8.3 to 23.6 mg L^?1 2,4‐D reduced disease incidence in pot trials, and from 10.8 to 41.0 mg L^?1 minimised disease severity in both pot and field trials. In only one pot trial, significant phytotoxicity was found with rates of 100 mg L^?1 or greater, reducing mean total tuber mass per plot and 38 mg L^?1 or greater, reducing mean mass per tuber. Notably, within the field trial, a more reliable plant growth system for estimation of yield, no significant impacts were observed. Disease control was associated with decreased sensitivity of tubers to thaxtomin A, the phytotoxin produced by the common scab pathogen essential for disease induction. The amount of residual 2,4‐D in tubers at harvest varied with cultivar, Russet Burbank accumulating more 2,4‐D than Desiree. Application rates less than 100 mg L^?1 resulted in levels of 2,4‐D below the Australian standard maximum residue limit. These data suggest that applications of 2,4‐D at low rates could provide a commercially suitable control strategy for common scab.     

Tuber proteins from haploids,selfs, and cultivars of group tuberosum separated by acid gel disc electrophoresis

Summary Tuber extracts of 46 cultivars (American varieties), and 350 haploids (2n=24) and selfs (2n=48) from four parents (2n=48), were analysed by acid gel disc electrophoresis. This system separated proteins into 12–14 bands. Twelve cultivars possessed unique patterns of bands, and the remaining cultivars could be placed in groups on the basis of 8 different banding patterns. Distinctions between varieties within groups was accomplished by either esterase or peroxidase isozyme patterns. The usefulness of basic gel proteins, esterase, and peroxidases for varietal identification is known; the acid gel protein patterns described provide a fourth system.Proteins from haploids and selfs were examined for variation in frequency and presence of bands. Differences among bands of the 4 parents were minor. Most haploids and selfs possessed the same bands as their parents, but there were interesting exceptions. The frequency of certain bands was significantly higher in selfs than in haploids. The results fit what would be expected if the parent tetraploid is simplex for a dominant allele controlling the production of each protein. Other bands are more frequent in haploids than selfs and some bands are present in haploids and not in the parent. Suppressor genes in the tetraploids may account for these latter results.

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Zusammenfassung Knollenextrakte von 46 Klonen amerikanischer Kartoffel-Sorten sowie von 350 Haploiden (2n=24) und Selbstungen (2n=48) von vier Eltern (2n=48) wurden mit Hilfe von Disk-Gel-Elektrophorese in saurem Milieu analysiert. Dieses System trennte die Proteine in 12–14 Zonen auf. Zwölf Klone wiesen einheitliche Proteinmuster auf. Die übrigen Klone konnten auf Grund von acht verschiedenen Proteinmustern in Gruppen eingeteilt werden. Unterscheidungen zwischen Sorten innerhalb dieser Gruppen wurden entweder anhand von Esterase- oder von Peroxydase-Isozym-Mustern vorgenommen.Die Brauchbarkeit von basischen Gel-Proteinen, Esterasen und Peroxydasen für die Kennzeichnung von Sorten ist bekannt; die beschriebenen ProteinMuster nach Gel-Elektrophorese im sauren Medium stellen ein neues, viertes System dar.Proteine von Haploiden und Selbstungen wurden im Hinblick auf Variationen in Häufigkeit und Auftreten von Zonen untersucht. Die Unterschiede innerhalb der Protein-Muster der vier Eltern waren geringfügig. Die meisten Haploiden und Selbstungen wiesen die gleichen Zonen auf wie ihre Eltern; jedoch kamen interessante Ausnahmen vor. Gewisse Zonen traten beträchtlich häufiger in Selbstungen als in Haploiden auf.Diese Ergebnisse sind zu erwarten unter der Annahme, daß der tetraploide Elter simplex für ein dominantes Allel ist, das die Synthese eines jeden Proteins kontrolliert.Andere Zonen zeigten sich häufiger in Haploiden als in Selbstungen. Einige Zonen traten nur in Haploiden, nicht aber im Eiter auf. Suppressor-Gene in den Tetraploiden könnten für diese Ergebnisse verantwortlich sein.

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Paper No. 1232 from the Laboratory of Genetics, University of Wisconsin. Supported in part by a grant from the Rockefeller Foundation.     

Freezing tolerance and tuber production in selfed and backcross progenies derived from somatic hybrids between Solanum tuberosum L. and S. commersonii Dun.

 Selfed and backcross progenies developed from tetraploid somatic hybrids between Solanum tuberosum (tbr) and S. commersonii (cmm) were characterized for nonacclimated freezing tolerance (NA) and acclimation capacity (ACC) (two independent genetic components of freezing tolerance) under controlled environments. The segregation covered 28% and 71% of the parental range for NA and ACC, respectively, with the distribution skewed toward the tbr parent. Therefore, ACC appeared to be relatively easier to recover in the segregating generation. Some first backcross progeny had greater freezing tolerance than the cultivated parent primarily through the increase in ACC. When grown in the field, the improved freezing tolerance observed in the selfed progeny under controlled conditions was confirmed. Among NA, ACC, and freezing tolerance after acclimation (AA, which is the cumulative performance of NA and ACC), AA exhibited the highest correlation coefficient with field frost tolerance. In addition to freezing tolerance, vine maturity and tuber traits including tuber yield, tuber number per plant, mean tuber weight, and specific gravity were also segregating. No significant correlation between undesirable tuber traits and freezing tolerance was detected. Vine maturity and freezing tolerance were significantly correlated, so more careful selection for earliness was necessary in incorporating freezing tolerance. Yield comparable or superior to the backcross parent Wis AG 231 and an early Canadian cultivar, ‘Sable’, was found in many backcross progeny and some selfed progeny. The observed high yield can be attributed to the increase in mean tuber weight as well as tuber number. Moreover, a high portion of progeny had a specific gravity higher than 1.085, and some greater than 1.1. The implications derived from this study in breeding for freezing tolerance and further use of these materials are discussed. Received: 22 August 1998 / Accepted: 4 January 1999