Tuberosum Group Research Articles

Utilization of potato genetic resources in variety development

Potato varieties of Europe, widely grown prior to the late blight epidemic of the 1840s, were apparently derived mainly from ChileanSolanum tuberosum Group (Gp) Tuberosum and with contributions from Gp Andigena. A small number of these old varieties had field resistance and consequently survived the late blight. These survivors, along with a limited number of 19th and early 20th century introductions, provided the very narrow genetic base for our modern potato variety development. Beginning in the first half of the 20th century, resistance to diseases and pests from exotic species and primitive relatives was backcrossed into the existing parental stocks, with little improvement in broadening of the genebase. By the 1980s, 77% of European and somewhat fewer North American varieties had genes, derived by backcrossing, fromS. demissum (late blight resistance) and Andigena (resistance to cyst nematode). Broadening of the Tuberosum genebase was undertaken in 1959 by creating long-day adapted Neo-Tuberosum (N-T) from large populations of Andigena. This took six or more cycles of recurrent mass selection. Simmonds, in England, was the first to begin this work, followed shortly after by Plaisted, in the U.S., and Tarn, in Canada. Varieties with N-T in their pedigrees include the New York releases “Rosa”, which is 50% N-T, and “Eva”, 25% N-T. The Tuberosum genebase has also been broadened with diploid Gp Phureja resulting in the releases of “Yukon Gold,”with yellow flesh and high internal quality, and “NorValley,”a chipper with resistance to cold sweetening. Over 5000 accessions of about 150 wild species are available to breeders from the U.S. Department of Agriculture, National Research Support Project 6 (NRSP-6) genebank. Many of these accessions have been evaluated for resistance to diseases and pests as well as other important traits. Six genebanks in other countries also have many accessions for breeders. These seven collections are a great source of valuable traits for breeding, but remain under-utilized, mainly because of the time and additional resources required in eliminating the “wildness”characters associated with the desired traits. “Pre-breeding”is needed to help breeders utilize the many needed genes and alleles in the wild species. There now are two projects with pre-breeding as an objective in the U.S., one at Madison, WI, and the other at Prosser, WA. Resistance to cold sweetening (low sugar build up in cold storage) has been backcrossed from several wild species into the Tuberosum background, as has resistance to late blight, the Columbia rootknot nematode, and the potato leafroll virus (PLRV). Resistance to potato virus Y (PVY) and PLRV obtained from N-T has been incorporated into Tuberosum parental stocks. Durable resistance to late blight in Polish breeding stocks, withS. demissum andS. stoloniferum background, and in improved Bolivian and Peruvian Andigena has also been utilized by North American programs.

Transfer of resistance to potato cyst nematode (globodera pallida) into cultivated potato Solanum tuberosum through first division restitution 2n pollen

Genetic resistance to potato cyst nematode is considered as one of the most effective means of increasing yield and reducing nematode infestation levels in potato fields. In this study, resistance to this nematode was successfully transferred from diploid tuber-bearing Solanums to the tetraploid gene pool using a 4x-2x breeding approach. More specifically, resistance from Solanum vernei, S. sparsipilum and haploids of S. tuberosum group Andigena was introgressed into conventional tetraploid clones, using first division restitution (FDR) 2n gametes. Furthermore, some of the FDR diploid parents had similar breeding values as advanced resistant tetraploid clones which were developed only after several cycles of selection against the potato cyst nematode.

The genetics of triploid formation and its relationship to endosperm balance number in potato

The ability of Solanum tuberosum Group Andigena clones to produce triploids (2n = 3x = 36) in 4x(4 endosperm balance number (EBN)) x 2x(2EBN) crosses was investigated. The difference in triploid production among the clones tested, though large, appears to be the result of low heritability. The triploids produced in the 4x x 2x crosses did not seem to bear heritable factors that improved triploid production in 2x and 4x populations derived from them. Yet, the seeds/fruit data from a similar 4x x 2x cross fit a Poisson distribution. It was argued that the low probability nonheritable random events responsible for the triploids from 4x x 2x and 2x x 4x crosses were misfertilizations, mitotic abnormalities in the gametophyte, and (or) mitotic misdivisions in the endosperm.

Immunity to Clavibacter michiganensis subsp. sepedonicus: Screening of exotic Solanum species

Accessions from exotic Solanum species, including diploid and tetraploid species, were screened for immunity to Clavibacter michiganensis subsp. sepedonicus, the causal agent of potato ring rot. The diploid species included S. infundibuliforme, S. lesteri, S. megistacrolobum, S. tuberosum Group Phureja, S. polyadenium, S. pinnatisectum, S. raphanifolium, S. sparsipilum, S. sanctae-rosae, S. tuberosum Group Stenotomum, S. toralapanum, and S. verrucosum. The tetraploid species included S. tuberosum Group Andigena, S. acaule, S. fendleri, S. hjertingii, S. oplocense, S. polytrichon, and S. stoloniferum. Apparent immunity was initially found in several diploid species, but was not present during subsequent retesting. Immunity was found in nine accessions of tetraploid S. acaule. These accessions maintained their immunity during testing over an eight-month period. S. acaule appears to be a good source of immunity for introgression studies.

Inheritance of potato chip color at the 24-chromosome level

Potato chip color is an important trait in determining quality and acceptability of cultivars for processing. Therefore, the genetics of potato chip color is important in varietal breeding. The use of 2xS. tuberosum Group Tuberosum haploid × 2x wild species hybrids provides disomic inheritance for genetic analysis of chip color. Two hundred forty haploid-species hybrids representing crosses between 15 haploids and 10 species were evaluated for potato chip color after 21 days reconditioning (18 to 20C) following 6 months at 4C. Phenotypic variation for chip color was found among the haploid-species hybrids. Crosses between good, medium, and poor performing clones were made in all combinations and 136 families were obtained. Progeny were evaluated for reversion resistance (chipping direct from 10C storage) and reconditioning (chipping from 4C after tuber warming) chip color. Variation for chip color was found among the progeny for each trait. Significant correlations between reversion resistance and reconditioning were found. Yet, the use of at least two chip tests (one for reversion resistance and one for reconditioning) is more informative than the use of one test and subsequent predictions made, regarding the other trait. A three locus hypothesis for both reversion resistance and reconditioning is proposed for the inheritance of each trait. One dominant allele at each of the three loci is necessary for good chipping. One or two loci may be common to both characteristics. Good chipping 2x hybrids that produce 2n pollen can be used to transfer this trait to the 4x level through use of 4x × 2x crosses.

The inheritance of anthocyanin pigmentation in potato (Solanum tuberosum L.) and mapping of tuber skin colour loci using RFLPs

Two existing genetic models for anthocyanin pigmentation are compared: the genetic model as proposed by Lunden (1937, 1960, 1974) for tetraploid potato Solanum tuberosum group Tuberosum and the model by Dodds & Long (1955, 1956) for diploid cultivated Solanum species. By crossing well defined genotypes from both genetic sources it was demonstrated that locus R/Rpw and locus D are allelic. Both loci are involved in the biosynthesis of red anthocyanins. We propose to maintain the symbol D for this locus. Tuber skin colour is expressed due to the complementary action of one locus involved in anthocyanin biosynthesis and a second locus involved in tissue-specific regulation of anthocyanin expression. The inheritance of two phenotypes of skin colour was investigated in this study: pigmentation of the epidermis and pigmentation of the cortex. In two different populations the loci determining the two phenotypes were located with RFLPs on the map of the potato genome, at approximately the same position as the earlier mapped PSC locus on chromosome 10. Lunden proposed the symbols E and R for the loci determining these phenotypes. Dodds and Long proposed only one locus I for tuber skin colour without describing these different phenotypes. The identity and nomenclature of the loci studied by the various authors are discussed.

Potato germplasm with combined resistance to leafroll virus and viruses X and Y

Potato germplasm with high levels of combined resistance to potato viruses X, Y, and leafroll was identified and used to produce improved parental clones with similarly high levels of resistance. Resistance was determined from the amount of tuber infection following inoculation of plants in the field. Parental germplasm with the best multiple resistance came from two backgrounds, eitherSolanum tuberosum group Andigena derived from the Cornell University neo-tuberosum program, or from complex hybrids ofS. tuberosum and wild solanums that were produced by the Max Planck Institute and the Polish Institute for Potato Research. Two Aberdeen, ID selections, A85519-6 and A85530-10, with gp. Andigena ancestry, have had no tuber-borne infection of PVX, PVY, or PLRV during four years of intensive field testing. We have not been successful in combining virus S resistance with resistance to the other viruses.

Transmission and yield effects of a gibberellin mutant allele in potato

A selected clone ofSolanum tuberosum Group Andigena PI 347773 (clone Adg 11.1) and the cultivar Superior had previously been shown to be heterozygous at a gibberellin related dwarfing locus, ga1. Experiments were conducted to test for gametophytic selection for alleles at the ga1 locus in reciprocal crosses and for the effect of genotype on tuber yield. The genotypes of individuals from superior-Adg 11.1 reciprocal F1 families were determined by test crossing. Genotypic classes could be distinguished by the percentages of dwarf seedlings in their test cross progeny. No differences were found in the genotypic distributions of the reciprocal families, which indicates gametophytic selection at this locus is not the cause of reciprocal yield differences. Superior-Adg 11.1 individuals classified by ga1 locus genotype were evaluated for tuber yield. Tuber yields were highly correlated with genotype in both reciprocal families. Yields followed the pattern of simplex>duplex>triplex, indicating that the recessive mutant ga1 allele exhibited a dose effect stimulating yield.

A restorer gene for genetic-cytoplasmic male sterility in cultivated potatoes

Fifty-nine clones (cultivars and advanced selections) ofSolanum tuberosum Group Tuberosum were pollinated with two Group Phureja-haploid Tuberosum hybrids, which produce FDR 2n pollen (ps/ps) and are heterozygous for a dominant gene (Ms/ms) which interacts with Tuberosum cytoplasm to result in male sterility. Twenty-eight and thirty-four plants from each family were transplanted to the field in two different locations, respectively. Pollen samples were collected from each plant and stained with acetocarmine glycerol jelly. Plants with over 95% unstainable pollen were considered male sterile. The families could be put into distinct classes according to the ratio of male sterile to male fertile plants; 3 sterile: 1 fertile (23 clones), 2 sterile: 3 fertile (24 clones), 1 sterile: 5 fertile (3 clones), and 0 sterile: 1 fertile (3 clones). Four families deviated significantly from any expected ratio. The variation for male fertility among families resides in the tetraploid parent, since the male parents have the same genotype (Ms/ms) for theMs locus. The locus of this gene is very distal to the centromere such the 2n gametic output is 1 Ms/Ms : 2 Ms/ms : 1 ms/ms. The variation in male sterility is explained by the presence or absence of a dominant allele of a restorer gene (Rt) in tetraploid Tuberosum. This locus is also very distal to the centromere. The frequency of theRt gene was estimated to be 0.20 in Tuberosum. The finding ofRt gene explains some of the conflicting results in male fertility of haploid Tuberosum x 2x cultivated and wild species hybrids. It also provides an opportunity to partially circumvent this male sterility. Haploids (2n = 2x = 24) extracted from 4x clones withRt genes would have male fertile progeny in crosses with species carrying theMs gene.

Characterization of a new gibberellin related dwarfing locus in potato (Solanum tuberosum L.)

Gibberellins have been shown to be involved in such important processes as seed germination, flowering, maturation and tuberization in potato. Parents fromSolanum tuberosum Groups Andigena and Tuberosum were found to produce progeny containing dark green, rosette dwarf individuals which could be completely restored to normal appearance by exogenous GA3. Test crosses indicated that this phenomenon can be explained by the action of a single locus, the dwarfing characteristic being conferred by the nulliplex condition. The gene symbol “ga1” is proposed. Group Andigena dwarfs demonstrated much greater tuberization compared to their normal full sibs or dwarfs restored to normal phenotype by exogenous GA3. The possibility that such gibberellin mutants may be involved in the long day adaptation of Gp. Tuberosum is discussed. This character may also be a useful tool for investigating various aspects of the gibberellin status of the potato.

Two new blackfly species of Simulium (Simulium) from Java, Indonesia (Diptera: Simuliidae).

Two new blackfly species, Simulium (Simulium) sigiti sp. nov. and S. (S.) javaense sp. nov. are described based on the female, male, pupal and larval specimens collected from Java. Simulium (S.) sigiti is characterized by the presence of a pit-like cuticular organ at the base of pupal gill, as well as shortened pupal filaments. This is the first species of the tuberosum group from Java. The variety of S. (S.) iridescens De Meijere, 1913 is here elevated to the species status and is given a new specific name S. (S.) javaense sp. nov. This new species is easily distinguished from S. (S.) iridescens by the inflated gill filaments, the absence of tubercles on the cephalic and thoracic integuments of the pupa, and the russet body coloration of the larva.

The Use of Potato Haploids to Put 2x Wild Species Germplasm into a Usable Form

AbstractAn effective method of incorporating germplasm of wild 2x Solanum species into the cultivated potato is through hybridization with haploids of 4x S. tuberosum Group Tuberosum. This procedure provides for the introduction of desirable traits and genetic diversity from wild species into potato. Haploid and wild species genotypes can be evaluated for parental value based on the presence of good tuberization, desirable traits, fertility, and 2n gametes in their hybrid progeny. Haploid‐wild species hybrids may be intercrossed and evaluated at the 2x level to take advantage of diploid genetic ratios. Selected 2x genotypes may then be brought to the 4x level through sexual polyploidization with 2n gametes.

Selection for Tuber Characters Can Maintain High Specific Gravity in a Diploid Potato Breeding Population

A base population of high specific gravity clones was established from a diploid hybrid population of Solarium tuberosum Group Phureja and Solarium tuberosum Group Stenotomum previously adapted to the long-day growing conditions in North Carolina. This base population was subjected to two 2-year cycles of recurrent selection. During each cycle, selections in the field were made on the basis of tuber smoothness, shape, and size. Tubers from unselected clones were bulked by plots. Tuber specific gravity was determined for the selected and unselected (bulk) clones. Tuber specific gravity was significantly greater in the selected than in the unselected clones in each cycle of selection.

Yield and yield components of meiotic tetraploids of potato

In a field study simulating commercial practice, the performance of 4x meiotic tetraploids from 4x−2x crosses (Group Tuberosum×(Group Phureja×haploid Group Tuberosum), and their 4x and 2x parents, was studied for total yield, total number of tubers, number of marketable tubers and average tuber weight. Some of the families showed striking heterotic effects for these characters. 38 selected high yielding tetraploids from these families, when evaluated in the next season, gave 80% higher mean yield than the mean of the 4x parents.

The agronomic value of tetraploid F1 hybrids between potatoes of Group Tuberosum and Group Phureja/Stenotomum

Selected tetraploid F1 hybrids, between Tuberosum cultivars and 2x Phureja clones, were compared with standard cultivars in randomized trials during the period 1980 to 1986 under conditions which simulated British agricultural practice. Hybrids were superior to standard cultivars in both total and marketable yield, and produced more tubers. We suggest that high yields in the 4x F1 hybrids result from the addition of complementary parental characters, high tuber numbers from Phureja and generally larger mean tuber size from Tuberosum. We discuss the relo of heterosis in an interploidy breeding scheme utilising unreduced male gametes and emphasise the value of tetraploid hybrids between Tuberosum and improved Phureja.

Heritability of Specific Gravity of Diploid Potato under High Temperature Growing Conditions

High temperatures encountered during the growing season reduce tuber dry matter content in commercial tetraploid potato (Solanum tuberosum L.). Variability in dry matter content as measured by specific gravity was observed in a diploid hybrid population of S. tuberosum Group Phureja and S. tuberosum Group Phureja and S. tuberosum Group Stenotomum grown under high temperatures. The objective of this research was to estimate heritability of specific gravity in this diploid hybrid population under high temperature growing conditions in North Carolina. Heritability was estimated by midparent offspring regression. Parents were grown at three high‐temperature locations and offspring at eight. Analyses of variance on specific gravity for each of the eight offspring locations revealed heterogeneity of error variances, therefore data were not combined over years and locations for further analyses. Twenty‐four estimates of heritability were obtained, 16 of which were unbiased (parents and offspring were grown in different years and different locations). The average unbiased estimate of heritability was 0.28 (range −0.07 to 0.77). Four estimates were biased because parents and offspring were grown at similar locations in different years. The average of these estimates was 0.57 (range 0.51‐0.63). Two estimates were biased because parents and offspring were grown in the same year in different locations, the average of which was 0.38 (range 0.29–0.46). Two estimates were biased because parents and offspring were grown in the same year at similar locations. These averaged 0.41 (range 0.40‐0.42). Considered together, the moderate estimates of heritability suggest that it should be possible to continue to improve this population for specific gravity under high‐temperature growing conditions. There was an apparent upward bias in the heritability estimates when the parents and offspring were not grown in different years and different locations.

Potato breeding with haploids and 2n gametes

Potato breeding methods that utilize haploids of Solanum tuberosum group Tuberosum or group Andigena and 2n gametes exploit the genetic diversity, including both valuable traits and allelic diversity, available in exotic germ plasm. Three essential components are involved: (i) the wild and cultivated 2x relatives of the cultivated 4x potato are a valuable source of genetic diversity; (ii) haploids (2n = 2x = 24) of cultivars (2n = 4x = 48) are effective in capturing diversity (germ plasm enhancement); (iii) 2n gametes, resulting from first division restitution, are an efficient method of transmitting this genetic diversity to cultivated 4x potatoes. Heterosis for total and marketable tuber yield and specific gravity occurs in 4x families from crosses between 4x cultivars and 2x haploid Tuberosum × 'Phureja' hybrids. Selected 4x clones from relatively small 4x × 2x families have been released as cultivars based on their earliness and heat tolerance in the tropics. Other 4x clones from 4x × 2x crosses, where the 2x parents were haploid – wild species hybrids, have good yield, excellent tuber type, high specific gravity, low reducing sugars, storage quality, and stress tolerance. The seedling vigor, uniformity, and large tuber yields of progeny from 4x × 2x crosses also makes this an effective breeding method for producing potatoes from true potato seed. This breeding method is also being successfully exploited in alfalfa, red clover, sweet potatoes, yams and several species of grasses, fruits, and ornamentals.Key words: potato, haploids, 2n gametes, germ plasm, allelic diversity.

Effect of environment and direction of hybridization on genetic variability in two diploid potato populations

Twelve selections from each of theSolanum tuberosum Groups haploid Tuberosum and Phureja were intercrossed in a NC Design II pattern to generate reciprocal hybrids. Yield parameters, combining ability and variance components were estimated from field experiments conducted at three locations, one in Minnesota and two in Morocco. Heterosis for yield and tuber number was significant at all locations, but only in Tuberosum cytoplasm. Estimates of general combining ability (GCA) for Tuberosum parents and specific combining ability (SCA) for Tuberosum-Phureja combinations varied with location and direction of hybridization. GCA of Phreja parents, however, was consistently significant at all locations and in both cytoplasms. Genetic variance estimates revealed predominantly non-additive gene action for most traits. Environment and direction of hybridization significantly influenced estimates, of variance components, indicating that hybrid performance should be evaluated in both cytoplasms and in the target environments for effective utilization of this germplasm in future breeding efforts.

Reciprocal differences between hybrids of Solanum tuberosum Groups Tuberosum (haploid) and Phureja

Yield components including total tuber yield, total tuber number, vine maturity, vine vigor and average tuber weight as well as seed germination and pollen stainability were studied in 28 exact reciprocal hybrid families, between 12 Solanum tuberosum Group Tuberosum (haploid) (TH) and 12 S. tuberosum Group Phureja (PH) clones in a NC Mating Design II in 4 sets of 3 by 3 reciprocal hybrids at three locations, one in Minnesota (USA) and two in Morocco. TH parents were insensitive to daylength whereas most PH clones required critical photoperiods equal to or less than 14 hours for tuberization. Mean reciprocal differences were significant for most traits at all 3 locations. Hybrids with TH cytoplasm were superior to those with PH cytoplasm by 18% for tuber yield, 21% for tuber number, and 9% for vine maturity, but inferior to hybrids with PH cytoplasm by 11% for vine vigor and 19% for time to reach 80% seed germination. Reciprocal differences were not detected for average tuber weight. Six reciprocal crosses revealed significant differences for pollen stainability but the overall mean difference (one location) was not significant. Possible reasons for the observed reciprocal differences included gamete selection, pseudo-self-compatibility and/or interaction of cytoplasm with both nuclear genes and environment. Differences for critical photoperiod of TH and PH parents were also demonstrated as a probable source of reciprocal differences.

Potato remains from a late pleistocene settlement in southcentral Chile

Taxonomic and evolutionary relationships between the Chilean cultivars ofSolanum tuberosum and the wild speciesS. maglia are explored. Widely separated centers of origin are postulated for the Group Tuberosum and Group Andigena varieties of the common potato. The first group is believed to have been domesticated originally in the humid forest-lands of southcentral Chile, while the second appears to have arisen in the high, cold Andes of Peru and Bolivia. In connection with the origin of the Group Tuberosum varieties, a 13,000-yr-old specimen ofS. maglia from the archaeological site of Monte Verde, Chile, is illustrated and described for the first time. These remains, the oldest on record for any wild or cultivated potato species, are important in that they help to establish the area of southern Chile as one of two main centers for evolution of the common potato.