Chromosome Number Manipulation as Part of Potato Pre-breeding Programs

The cultivated potato(Solanum tuberosum L.) is a tetraploid(2n=4x=48) and can be improved with the incorporation of desirable traits from other Solanum species.Often the transfer of these traits is hindered by complex genetics and breeding barriers within potato.Parthenogenesis and microsporogenesis are used in chromosome number manipulation allowing breeders to reduce the potato's chromosome number to dihaploid(2n=2x=24)[diploid] or monohaploid(2n=x=12) from which a predictable transfer of traits can be made,in accordance with the endosperm balance number theory(EBN).Furthermore,the reproductive processes of first division restitution(FDR) and second division restitution(SDR) are utilized in order to increase the chromosome number for incorporation into the cultivated potato.     

The inheritance of resistance to soft rot (Erwinia carotovora subsp.atroseptica) in diploid potato families

Soft rot of potato tubers, caused byErwinia (Pectobacterium), is a serious disease affecting potato crops during storage. Studies on the inheritance of resistance to tuber soft rot were undertaken on diploid potato hybrids. A total of 480 clones, derived from 12 families, were examined for resistance to soft rot in laboratory tests over 3 years and for basic agronomic traits in field experiments over 2 years. General (GCA) and specific (SCA) combining abilities were significant in the inheritance of resistance to soft rot; however, GCA for female parents were significant in 1 or 2 years during 3 years of evaluation and SCA was significant for eight, two, and six families out of 10 tested in 1994, 1995, and 1996, respectively. There were also significant differences between years. Moreover, marked interactions for GCA_females × year and SCA × year in the variation of soft rot resistance were found. Broad-sense and narrowsense heritability of resistance, measured as diameter of rotten tissue, was estimated as 0.92 and 0.89, respectively. The maternal effect, evaluated in two sets of reciprocal crosses, was not significant for the genetic determination of resistance to soft rot. No significant relationships were found between resistance to soft rot and the main agronomic traits in the tested diploid families. These results suggest that diploid potato clones with resistance to soft rot can be selected after being evaluated over a few seasons. It is also possible to select clones combining good resistance to soft rot with high yield, superior tuber characteristics, and acceptable starch content. These resistant diploids can be used as male parents in 4x-2x crosses in breeding tetraploid potato resistant to soft rot.     

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.     

Inheritance of tuber shape in cultivated diploid potatoes

The inheritance of tuber shape was studied by developing and/or selecting clones from a cultivated diploid potato breeding program. Progeny analyses indicated that one major gene controls the round and long shapes. Round is dominant over long. The gene symbol Ro, earlier proposed by Masson, is accepted. All three possible genotypes, RoRo, Roro and roro were identified. Ro was found to be linked with I, a previously described gene which controls the expression of anthocyanin in the tuber skin. In nearly all genotypes studied the linkage was in the coupling phase; however, one parent was identified where the linkage was in the repulsion phase. The recombination frequency between Ro and I was found to be approximately 11.8%. The implication of linkage between tuber skin color and shape is discussed.     

Diploid Potato Hybrids as Sources of Resistance to Blackspot Bruising

Resistance to bruising is an important quality trait of potato depending on multiple genetic and environmental factors. Thirty one interspecific diploid hybrids and two tetraploid standards were evaluated for resistance to bruising in 2 years. Diploids originated from crosses between wild and primitive Solanum species and dihaploids of S. tuberosum. Two-year mean values of bruising resistance of tested genotypes indicated significant variability of the trait. Analysis of variance showed significant effects of genotype, year and interaction between them on the trait. Broad-sense heritability of bruising resistance was estimated as moderately high, Hb?=?0.73. Content of L-tyrosine, the main substrate of discoloration reaction, was not significantly correlated with brusing in tested diploid hybrids. The clones, that were resistant to blackspot bruise, also combined quality traits and resistances to many pathogens. All these traits could be transferred together into tetraploid level in 4x?×?2x crosses via male 2n gametes produced by diploid hybrids.     

芸薹属二倍体种的基因组结构及细胞遗传学研究进展

本文综合分析了细胞遗传学及比较基因组学在芸薹属栽培种基因组结构及进化方面的研究进展。测序物种的DNA序列比较分析显示，芸薹族特有的六倍体祖先基因组的进化途径为，先由芸薹科x=8的祖先核型衍生出染色体数减少的x=7的核型，然后该核型经过三倍化事件产生古老的六倍体基因组，最后才分化产生3个芸薹属栽培二倍体种。根据3个二倍体种测序基因组的比较分析，构建了具有9条染色体的芸薹属祖先基因组及所形成的二倍体的染色体组成。传统及分子细胞遗传学研究为二倍体种基因组的多倍体性质及部分同源性关系提供了直观的证据，特别是二倍体间的异源染色体附加系的减数分裂配对行为揭示了单条染色体间的同源性程度。最后，对依据近缘物种的基因组结构进行芸薹属作物种质资源的创建与利用提出建议。     

彩色马铃薯花色苷生物合成相关基因的研究进展

关键酶基因表达量决定了花色苷含量的高低,综述国内外对彩色马铃薯花色苷生物合成途径以及相关基因的研究现状,多个相关酶基因已经通过二倍体或四倍体马铃薯完成了cDNA的克隆,研究发现部分酶基因的启动子容易受到UVB辐射、低温等外界环境条件的诱导。对以后的研究工作提出了建议,希望能够为马铃薯花色苷的开发利用和生物合成相关基因的克隆、表达分析以及马铃薯分子育种提供参考依据。     

Seed protein variation within accessions of wild and cultivated potato species and inbredSolanum chacoense

Summary Soluble proteins in seed potato were analyzed by electrophoresis (PAGE). The Index of Variation (IV) was calculated in order to estimate variation within each accession of wild and cultivated potato species andS. chacoense selfed lines. Seeds of 34 accessions representing 14 species from six taxonomic series were analyzed. The IV ofS. chacoense selfed lines decreased from 47.7 in the S₂ to 12.9 in the S₇ generation. The average IV for the self-incompatible diploid species was 41.2, whereas that of the selfcompatible diploid species,S. polyadenium, was 21.3. TetraploidS. tuberosum ssp.andigena andS. sucrense had an average IV of 62.2, which is much higher than that observed in any other diploid species. The naturally selfing speciesS. acaule (4x), and its colchicine-doubled derivative (8x), showed very low variation (IV=7.5). The IV appears to reflect heterozygosity and is affected by the breeding mode and the genetic constitution of diploid parents for derived polyploids.     

Resistance to soft rot (Erwinia carotovora subsp.atroseptica) in tetraploid potato families obtained from 4x-2x crosses

Diploid potato clones, interspecific hybrids ofSolanum species, having in their originS. tuberosum,S. chacoense, S. yungasense, S. phureja, S. gourlayi, andS. demissum, with resistance to soft rot, were crossed to tetraploid potato clones in 4x-2x crosses. The 24 tetraploid families obtained in a North Carolina II design were examined for tuber resistance to soft rot in a laboratory test and for basic agronomic traits in field trials conducted for two consecutive years. In addition, one family originating from a 4x-2x cross of two susceptible parents was tested. Statistical analysis of the data revealed significant general (GCA) and specific combining ability (SCA) effects, year, GCA (female) × year, GCA (male) × year, and SCA × year upon the inheritance of resistance to soft rot. About 35% of the progeny was selected as resistant to tuber soft rot, and of these 11% showed high resistance combined with good tuber yield, tuber weight, and tuber appearance. The relationships between resistance to soft rot and chosen agronomic traits were not noted or were weakly significant and sporadic. The resistance to tuber soft rot found in diploid potato hybrids can be transferred to the cultivated tetraploid pool through 4x-2x crosses, and a high frequency of offspring posses resistance.     

Minimizing inbreeding in tetraploids derived through sexual polyploidization

Diploid (2n = 2× = 24) potato (Solarium) species that produce 2n gametes are being utilized in potato breeding programs. Three breeding schemes involving these diploids are presently used by potato breeders to transfer this genetic material from diploid parents to their tetraploid offspring. Derived tetraploids may arise through tetraploid × diploid, tetraploid × haploid-species, or diploid × diploid hybridizations. The inbreeding coefficient of derived tetraploids is a complex function of the coancestry of the parents, the inbreeding of the parents, the coefficient of double reduction in the tetraploid parent, and the frequency of single exchange tetrads in the diploid parent(s), and it depends on the mechanism of 2n gamete formation. For the two breeding strategies involving tetraploid female parents, there is less inbreeding in the derived tetraploid from a diploid parent producing 2n pollen by first division restitution than 2n pollen by second division restitution when the frequency of single exchange tetrads in the diploid is less than 2/3. In bilateral sexual polyploidization, the inbreeding coefficient of a derived tetraploid for a given set of parents from a first division × first division restitution cross is less than the inbreeding coefficient of a second division × first division restitution cross which is less than the inbreeding coefficient of a second division × second division cross when the frequency of single exchange tetrads is less than 2/3.     

Inheritance of pigmented tuber flesh in cultivated diploid potatoes

In a genetic study with cultivated diploid potatoes the distribution of anthocyanin to the tuber flesh was found to be controlled by a single dominant allele. The gene symbolPf (pigmented flesh) is proposed. The geneI, which controls the distribution of pigment to the tuber skin, is necessary for the expression ofPf and is closely linked to thePf locus. ThePf gene is a potentially useful genetic marker which does not appear to be associated with any deleterious traits and can be screened for without laboratory equipment.     

The current status of knowledge on the cellular biology of potato

Summary Conventional potato breeding does not make full use of the existing biodiversity within theSolanum genus. Moreover breeding at the 4x-4x level is slow. The potential for breeding at the diploid and dihaploid levels has therefore been explored. This requires use of novel techniques to overcome deviations from the desired Endosperm Balance Number. Somatic hybridization approaches include symmetric and asymmetric hybridizations and cybridization. Interesting traits have been successfully transferred through these techniques. Introgression and chromosome elimination have profited from the recent and rapid development of analytical techniques such as RFLP and RAPD. Cellular approaches in potato breeding may be combined with conventional breeding by a stepwise reduction of the ploidy level followed by resynthesis of a new heterozygous tetraploid clone. Such schemes have been used to include virus or nematode resistance. Haploids may be derived from different sources or obtained through different techniques. Dihaploid-dihaploid breeding programmes may be especially interesting. Because of this potential, cellular biology of potato deserves the continued interest of the scientific community.     

Insert copy number,chromosome number,pollen stainability,and crossability ofAgrobacterium-transformed diploid potato

Two 2n-pollen producing cultivated diploid, 2n = 24, potato genotypes DM56.4 and US-W5337.3 were inoculated with binaryAgrobacterium vectors. The T-DNA contained a neomycin phosphotransferase II coding region fused to a nopaline synthase promoter providing gene expression in plants and resistance to kanamycin. A total of 28 clones regenerated as adventitious shoots from callus tissue, growing on medium with kanamycin, was analyzed for chromosome number, pollen stainability, and crossability. Several clones were tested and found to retain crossability with diploid and tetraploid clones. Nine out of 10 of the regenerants from DM56.4 had been doubled; seven of these were tetraploids with 2n = 48, one clone had 2n = 49, and another 2n = 46. Five of 14 regenerants of US-W5337.3 had been doubled, and three of these had fewer than 2n = 48. Pollen stainability revealed that the tetraploid regenerants from DM56.4 were male sterile, whereas tetraploids from US-W5337.3 had stainable pollen. All of the diploid regénérants produced 2n pollen. Crossability of several diploid and tetraploid regenerants was high. The number of T-DNA inserts revealed by Southern blot analysis was also determined. Six, 10, and 9 regenerants had 1, 2, and 3 inserts of T-DNA, respectively. There were single regenerants each with 5, 6, or 7 inserts. Selection for higher insert number among regenerants should be feasible based on the range of insert number found. Identical restriction patterns within three groups of clones indicated that the 28 clones analyzed emerged from only 21 cells derived from independent transformation events. The variability in chromosome number and pollen stainability suggests that variation in other traits would be obtainable.     

Towards F<Subscript>1</Subscript> Hybrid Seed Potato Breeding

Compared to other major food crops, progress in potato yield as the result of breeding efforts is very slow. Genetic gains cannot be fixed in potato due to obligatory out-breeding. Overcoming inbreeding depression using diploid self-compatible clones should enable to replace the current method of out-breeding and clonal propagation into an F₁ hybrid system with true seeds. This idea is not new, but has long been considered unrealistic. Severe inbreeding depression and self-incompatibility in diploid germplasm have hitherto blocked the development of inbred lines. Back-crossing with a homozygous progenitor with the Sli gene which inhibits gametophytic self-incompatibility gave self-compatible offspring from elite material from our diploid breeding programme. We demonstrate that homozygous fixation of donor alleles is possible, with simultaneous improvement of tuber shape and tuber size grading of the recipient inbred line. These results provide proof of principle for F₁ hybrid potato breeding. The technical and economic perspectives are unprecedented as these will enable the development of new products with combinations of useful traits for all stakeholders in the potato chain. In addition, the hybrid’s seeds are produced by crossings, rendering the production and voluminous transport of potato seed tubers redundant as it can be replaced by direct sowing or the use of healthy mini-tubers, raised in greenhouses.     

Solanum antacochense,a new wild Peruvian species

The largest concentration of wild tuber-bearingSolanums in the Western Hemisphere is located in the Andean region of Perú. However, in spite of the many potato collecting expeditions which have carried out extensive field work in the past, there still remain new species to be presented to science for the first time.Solanum antacochense, from the series tuberosa, a diploid species (2n = 2x = 24 chromosomes) native to Perú described here, is one of them.     

Crude Protein Content in Diploid Hybrid Potato Clones of Solanum phureja–S. stenotomum

Breeding potato (Solanum tuberosum L.) with high protein content is important for food value and for the processing sector to extract protein from potatoes. Due to the narrow genetic base of the common potato, a new germplasm has to be explored for breeding high-protein potatoes. The objectives of this research were to quantify the crude protein content of diploid hybrid Solanum phureja–Solanum stenotomum (PHU-STN) genotypes, determine the correlation of crude protein content with dry matter and other important agronomic traits, and estimate broad sense heritability for crude protein content. In 2008 and 2009, 70 diploid clones were grown in replicated field plots in Jiagedaqi, Heilongjiang. Also, two tetraploid potato cultivars, Kexin 2 (table potato) and Atlantic (high dry matter), were included in this experiment as controls. The crude protein content on a fresh weight basis (FW) over replications and years for PHU-STN clones ranged from 2.85% to 5.01% with a grand mean of 3.72%, and most of these clones were significantly or highly significantly higher in crude protein content than the two tetraploid controls. Correlations between crude protein content and agronomic traits were all negative, but the magnitudes were generally weak or moderate. Therefore it should be possible to select diploid clones with high crude protein content and acceptable agronomic traits. The estimate of broad sense heritability for crude protein content (FW) on a clonal mean basis was 0.66 with a 95% confidence interval of 0.46 to 0.79, whereas for crude protein content on a dry weight basis the estimate of broad sense heritability was 0.65 with a 95% confidence interval of 0.43 to 0.78. These results suggest that these diploid hybrid PHU-STN clones would be a good germplasm source for a high-protein-breeding effort, and identification of tetraploid progenies with high protein content and acceptable agronomic traits from 4x–2x cross should be possible.     

马铃薯抗青枯病和低温糖化体细胞杂种的鉴定

ACC-1-1和ACC-1-2再生株系由来自马铃薯二倍体栽培种(Solanum tuberosum)品系AC142-01(2n=2x=24)和二倍体野生种S.chacoense的一个无性系C9701(2n=2x=24)经原生质体融合获得,经鉴定为体细胞杂种。流式细胞仪分析和染色体计数显示,ACC-1-1为混倍体,ACC-1-2为八倍体。两个株系均能正常开花但花粉活力较低。花粉母细胞减数分裂观察显示,两个系在减数分裂各个时期均出现广泛的异常染色体行为,可能是花粉活力低的原因。青枯病接种鉴定表明,ACC-1-2对青枯病表现为高抗,而ACC-1-1表现为中感,同时这两个株系均具有"低温糖化"抗性,证明体细胞融合加上适当选择可以有效聚合有性杂交不亲和双亲的优良性状。     

利用体细胞杂交获取马铃薯软腐病的抗性

对马铃薯四倍体栽培种和二倍体野生种Solanumbrevidens的体细胞杂种通过叶片离体培养获得的四倍体植株,以及用四倍体栽培种进行回交获得的五倍体植株的块茎对软腐病的抗性进行了测定。结果表明,由体细胞杂种通过叶片组织离体培养再生植株中,有一个株系SC107对软腐病菌Erwiniacarotovora具有较强的抗性。在用不抗软腐病的马铃薯栽培种对体细胞杂种进行回交获得的杂种后代中,大部分株系对软腐病菌具有高水平的抗性,从而说明Solanumbrevidens对软腐病的抗性基因已转移到马铃薯栽培种。     

Breeding studies in potatoes containing high concentrations of anthocyanins

Studies of the breeding behavior of clones containing high levels of anthocyanins were conducted. Red-fleshed clones appeared in proportions suggesting multigenic control of degree of pigmentation. Red-fleshed and pur-ple-fleshed clones were always accompanied by red and purple skin, respectively. Red flesh ranged from partial pigmentation to complete pigmentation represented by pigment present in all tuber tissues. Percentage of com-pletely red-fleshed progeny was 14.5% and 4.1% in red x red crosses vs red × white (or the reciprocal), respectively. Purple-fleshed progeny were obtained from red x white crosses where the white-fleshed parent harbored theP pigment gene in juxtaposition with the nulliplex recessive state of theI gene (i.e.,iiii), which suppressed expression. Total anthocyanin ranged from 6.9 to 35 mg per 100 g fresh weight in the red-fleshed and 5.5 to 17.1 in the purple-fleshed clones. Red-fleshed clones contained predominantly acylated glycosides of pelargonidin while the purple-fleshed clones contained predominantly acylated glycosides of petunidin and peonidin. Oxygen Radical Absorbance Capacity and Ferrous Reducing Ability of Plasma revealed that the antioxidant levels in the red or purple-fleshed potatoes were two to three times higher than white-fleshed potato.     

Germplasm Release: Three Tetraploid Potato Clones with Resistance to Common Scab

Common scab caused by the soil-borne bacterium Streptomyces scabies is a serious disease for the potato industry. We have identified a strong source of resistance in the diploid wild relative Solanum chacoense. This resistance has been introgressed into tetraploid cultivated potato via unilateral sexual polyploidization. This paper describes three hybrid clones (M8, M16, M17) for use by potato breeding programs to enhance resistance to common scab. They were created by crossing a diploid clone (50% S. tuberosum, 50% S. chacoense) to tetraploid cultivars, producing hybrids with 75% cultivated and 25% wild germplasm. The clones are male and female fertile, and are adapted to temperate zone production environments.