The effect of seed tuber weight on characters in the first and the second clonal generation of potato populations

Summary Fifty-five populations from crosses of three Solanum tuberosum ssp. tuberosum cultivars and seven selected S. tuberosum ssp. andigena clones adapted to the northern temperate zone have been studied in the seedling and the first and second clonal generation. This paper only deals with the effect of seed tuber weight on various important agronomic characters which are selected for in early clonal generations, independently of the type of crosses.The results showed that a distinction has to be made between the effects of differences in seed tuber weight within and between seedlings, i.e. genotypes. The effects on the first clonal generation of differences in weight of the tubers within seedlings and those of the first heaviest tubers between seedlings were similar and comparable to seed tuber weight effects within cultivars. In contrast to the within seedlings effects the between seedlings effects proved to be heritable. This is concluded from the fact that, on average, independent of seed tuber weight seedlings with larger first heaviest tubers performed better in the second clonal generation than those with smaller ones. Notably plant height, general impression, date of maturity and particularly tuber yield and mean tuber weight in the second clonal generation were related to the weight of the first heaviest tubers of the seedlings. The potentialities of these findings for an early generation selection are discussed.     

Early generation selection for potato tuber quality in progenies of late blight resistant parents

Developing disease resistant cultivars is one of the major objectives for a potato (Solanum tuberosum L.) breeding program, but many resistant clones have not achieved commercial acceptance because of late maturity and non-marketable tuber characteristics. Selection for tuber quality should have greater emphasis inbreeding disease resistant cultivars. The objectives of this study were 1) to evaluate the ability of late blight (Phytophthora infestans (Mont.) de Bary) resistant parents to transmit chip-processing (tuber appearance, specificgravity, and chip-color) or tablestock (tuber appearance) quality to the offspring and 2) to compare selecting for tuber quality in single-hill versus eight-hill generations. We made crosses among eight unadapted potato cultivars (B0718-3,Bertita, Bzura, Greta, Libertas, Stobrawa, Tollocan, and Zarevo) with reported late blight resistance with adapted susceptible cultivars/breeding clones to generate 95populations (4,750 seedlings). Approximately 10% of the progeny from each cross were selected from single-hill plots based on tuber appearance, number, shape, and internal defects. These selected clones (408) were evaluated for tuber appearance, specific gravity, and chip-color. The same evaluations in the following year were made on tuber samples from eight-hill plots. Libertas and Tollocan were the best parents for transmitting chip-color; B0718-3, Zarevo, and Tollocan for transmitting tuber appearance; and Bzura, Libertas, and Zarevo for transmitting high specific gravity to the highest percentage of the offspring. Overall, 50% and 56% of the clones based on single- and eight-hill generation, respectively, were considered to possess chip-processing quality; over 90% of the clones had acceptable tablestock quality. A total of 71% of the clones possessing acceptable chip-processing and 95% of the clones possessing acceptable tablestock quality selected in both generations were identified in single-hill plots. The evaluation of tuber quality characteristics in single-hill generation not only permitted the identification of clones with acceptable chip-processing and tablestock, but also increased the amount of clonal information for the following generation of selection. In crosses between late blight resistant and susceptible clones, selection for tuber quality traits can be initiated in single-hill generation using a moderate selection intensity and precede late blight testing. This revised version was published online in August 2006 with corrections to the Cover Date.     

A breeding method for accelerated development of cold chipping clones in potato

Summary The development of potato cultivars having acceptable chipping quality after cold storage is important because it reduces costs to growers while ensuring continuity of supply to processors throughout the year. Over 5100 single-hill progenies were planted to select for cold chippers. A breeding procedure for selecting and evaluating these progenies for cold chipping ability was used, and 38 desirable genotypes were identified. These selections were increased in the second clonal generation and evaluated for yield, specific gravity, and seven chipping treatments of varying storage duration/temperature/reconditioning duration and were compared to standard chipping cultivars Atlantic, Monona, Norchip, and Snowden. Twenty-two selections yielded Norchip the highest yielding cultivar, while 15 selections had a specific gravity Atlantic, the highest specific gravity cultivar. Snowden was the best chipping cultivar overall and some selections were not significantly different than Snowden. Overall, nine selections combined high yield and specific gravity with the ability to produce attractive chips from 4° C. Single-hill selection for cold chipping could potentially save four years in the breeding process by the identification of good parents, the recycling of good parental cross combinations, and the evaluation of progeny for chipping earlier in the breeding program.     

Breeding for resistance to potato tuber moth,Phthorimaea operculella (Zeller), in diploid potatoes

Summary Sixty-two 2x families were generated by intermating 16, 2x clones and evaluated for resistance to potato tuber moth (PTM), Phthorimaea operculella under natural infestation in a storage at San Ramon, Peru and in laboratory tests. The following conclusions could be drawn: (1) relatively simple inheritance was observed for resistance derived from Solanum sparsipilum (spl), (2) the high level of resistance of the original spl has been transferred, undiminished, into an advanced 2x population, (3) simple phenotypic selection was successfully applied to transfer resistance into an improved 2x population, (4) there was a strong indication of reciprocal effects, however spl cytoplasm is not essential for the expression of nuclear resistance genes, (5) antibiosis and antixenosis are the mechanism of PTM resistance in this population, and (6) 4x × 2x crosses could be used to transfer the resistance into commercial cultivars.     

Optimising potato breeding. I. The genotypic,environmental and genotype-environment coefficients of variation for tuber yield and other traits in potato (Solanum tuberosum L.) under different experimental conditions

Summary Coefficients of variation for genotypic differences, genotype-location, genotype-year and genotype-location-year interaction were computed from reported data of potato trials in order to use them in a decision support system. The obtained coefficients of variation not only varied considerably between traits, but also between trials within traits. It is argued that only parameter values representative for the pertaining breeding situation should be used for optimising a selection programme.     

Correlations within and between characters between and within generations as a measure for the early generation selection in potato breeding

Summary The main objective was to determine the reliability of selection in early generations of a potato breeding programme. To that end data were recorded in the seedling generation, an early and a late harvested experiment of the first clonal generation and the late harvested second clonal generation on up to 30 genotypes of 55 populations from crosses of three Solanum tuberosum ssp. tuberosum cultivars and seven selected S. tuberosum ssp. andigena clones, adapted to the northern temperate zone. Phenotypic correlations were computed per population in almost all possible combinations within and between characters between and within generations. The mean across 55 comparable correlation coefficients was considered to be the best estimate of the relationship concerned.In all four experiments data were collected on number of tubers, tuber yield and mean tuber weight; in the three experiments of the two clonal generations in addition on date of emergence, number of stems, plant height, haulm type, and general impression of the underground plant parts and in the two late harvested clonal generations on date of maturity and under water weight.The results confirmed that general impression which is largely decisive for the selection in early generations, is a little reliable measure. However, from the magnitude of the mean correlations between experiments within characters it must be concluded that selection for most of these separate characters is hardly more reliable. An exception was date of maturity for which a mean correlation was determined of r=0.78 between the two clonal generations. The second strongest mean correlations, perhaps surprisingly, were for tuber yield, viz. r=0.52 between the seedling generation and the late harvested first as well as the second clonal generation and r=0.63 between the late harvested clonal generations. From the correlations between characters it appeared that for a high tuber yield, besides its components, in particular an early emergence, a large plant height, an attractive haulm type and a late maturity are of importance.The main conclusion is that, as long as not enough seed tubers are available for the layout of statistically sound experiments, a negative instead of a positive selection should be applied to avoid the rejection of most of the valuable genotypes in an early stage. On the basis of the results directives for the application of such a negative selection are given.     

Plant regeneration from callus culture in potato

Summary A procedure for plant regeneration from callus culture of potato, Solanum tuberosum L. is described. Calli were induced from 1–2 mm long shoot apices of potato cultivars Cara and A25/19 on half-strength Murashige and Skoog's medium (half-MS) supplemented with 3.2 mg IAA (indole-3-acetic acid), 1.0 mg kinetin (6-furfurylamino)purine], and 0.5 mg 2,4-D [2,4-dichlorophenoxy)acetic acid]/1. Sixty percent explants produced nodular calli on this medium within 30 days. Calli differentiated into shoot-primordia when subcultured on half-MS medium supplemented with 0.5 mg 2,4-D and 1.0 mg zeatin [6-(4-hydroxy-3-methybut-2 enylamino)amino purine]/1. Differentiated calli on half-MS medium without growth hormones produced complete plantlets which were cloned on the same medium and transferred into soil.     

Study on the inheritance of potato tuber yield by means of harvest index components and its consequences for choice of parental material

Summary The inheritance of potato tuber yield was studied considering the seasonal course of harvest index. Harvests of several progenies and their parents were performed at intervals and fresh weight of foliage, underground stems, tubers and stolons was assessed.Tuber yield depends on the time of tuber initiation and the proportion of the assimilates allocated to the tubers, as reflected in the increase rate of harvest index. The time of tuber initiation of the progenies was associated with the time of tuber initiation of the earliest tuberizing parent. The mean increase rate of the harvest index of the progenies was in most cases equal to the mean values of parents, however in crosses combining early with late maturing parents the rate equaled the value of the maternal parent. Using these relations, differences in harvest index between progenies can be predicted with a high degree of precision by using the harvest index parameters of the parents. This estimated harvest index showed a fairly good correlation to tuber yield at mid-September and can be used in the prediction of the yield of the progeny. The use of the mid-parent value for this purpose is not suitable.     

Performance and prediction of potato genotypes tested in international trials

Summary A series of international trials with the potato crop was conducted in eight countries representing widely differing environments. The purpose of the experiments was: (1) to develop a method for obtaining environmental indexes which measure productivity of diverse potato-growing areas, and (2) to construct performance models for individual genotypes based on the environmental indexes. Yield data of 32 genotypes obtained from a series of 13 experiments conducted in the eight countries in 1983 and 1984 were used in the study. The response pattern of the genotypes was studied by a multivariate analysis. Five genotypes were chosen as representatives for different response patterns to the environments and their data were used for calculating a series of independent indexes for each of the experimental sites based on principal component analysis. Performance models for each of the genotypes were constructed by stepwise regression analysis of yields of a genotype on the environmental indexes based on 1983 data. Yield data of 1984 experiments were used to verify the models. Satisfactory correspondence between observed and predicted yields was obtained for most of the genotypes.     

Breeding behavior for tuber protein in Solanum tuberosum and Tuberosum-phureja hybrids

Summary True protein content among tubers within a plant of Solanum tuberosum cv. Oneida was found to be negatively correlated with tuber size. A similar study of S. phureja genotype 148-17 revealed no correlation. Tuber protein was determined for 250 genotypes in each of four hybrid potato populations in a factorial mating design with four potato cultivars as stylar parents mated to four groups of pollen parents (4x cultivars, 4x high protein selections, 2x S. phureja, 2x high protein S. phureja). The hybrid population derived from the 4x high protein selections was significantly higher in protein content than the other populations. High estimates of general combining ability for tuber protein content were found for both stylar and pollen parents. Poor photoperiodic adaptation to growing conditions in northern latitudes was a possible explanation for the variable protein phenotypes typical of S. phureja and the lack of transmission of the high protein character in phureja to 4x-2x hybrids. Although protein content was negatively correlated with total yield, high protein segregates with good yield potential were identified in all four populations.Scientific Journal Series Article 11, 616 of the Minnesota Agricultural Experiment Station.     

Increased frost tolerance and amino acid content in leaves,tubers and leaf callus of regenerated hydroxyproline resistant potato clones

Summary A number of previously selected hydroxyproline (hyp) resistant cell lines of a diploid potato (Solanum tuberosum L., clone H²578, 2n=2x=24) could be regenerated into plants which were further analysed. Hyp resistance, although lower than in the originally selected calli, was still present in regenerated shoots and in callus initiated from these shoots and it was not lost upon (mini)tuber propagation. Regenerated shoots showed a wide range of phenotypic variation. The chromosome number, analysed in 4 clones, appeared to be hypotetraploid (44 or 45). Tuber-propagated regenerants generally showed increased frost tolerance both at the plant and the cell level. In leaves this seemed to be associated with increased levels of both proline and total amino acid content. However, in callus only the total amino acid content but not proline was still elevated. In the wild type the frost tolerance of the tubers appeared to be lower than that of the leaves. Between tubers of wild type and the hyp resistant regenerants no differences in frost tolerance were found, although proline and total amino acid content tended to be higher in tubers from the regenerants.     

Coagulable protein in potato: Screening method and prospects for breeding

Summary From tubers of 34 varieties of Solanum tuberosum, extracts were prepared and analysed for crude protein and coagulable protein by the Kjeldahl method. Content of coagulable protein was 0.37–1.24%. From the same material, juice was prepared with a juice centrifuge and analysed for coagulable protein by the Kjeldahl and microbiuret method. The average amount of coagulable protein in the juice was 81.8% of the total coagulable protein. The correlation coefficient between coagulable protein in the juice and total coagulable protein was 0.956. The correlation coefficient between Kjeldahl and microbiuret data for coagulable protein in the juice was 0.956. Analysis of tuber juice by the microbiuret method is recommended as a rapid screening technique for coagulable protein.Relationships between protein data of the 34 varieties and earliness, yield and content of dry matter were analysed statistically. Content of coagulable protein in fresh material correlated with content of dry matter (rs=–0.756), yield of fresh potatoes (r=–0.615) and earliness (r=–0.361) but not significantly with yield of dry matter (rs=–0.309). Coagulable protein in dry matter correlated with fresh yield (r=–0.525), but not significantly with content of dry matter (r=–0.260), yield of dry matter (r=–0.131) and earliness (r=–0.054). Path coefficient analysis showed that 67% of the variation in coagulable protein in fresh material was statistically determined by earliness, content of dry matter, fresh yield and content of uncoagulable protein in fresh material, whereas only 34% of the variation in content of coagulable protein in dry matter was determined by these components. A high content of coagulable protein in fresh or dry matter can be combined with early maturity and with high yield of dry matter. Coagulable protein in dry matter seems to be a more suitable criterion of selection than coagulable protein in fresh material.     

Somaclonal variation for resistance to Verticillium dahliae in potato (Solanum tuberosum L.) plants regenerated from callus

Summary Plant tissue culture is recognized as an important tool to generate useful genetic variability for crop improvement. Regenerated plants from callus induced from stem explants of Solanum tuberosum cv Désirée were assessed by in vitro selection, for resistance to Verticillium dahliae. This fungus is the causal agent of Verticillium wilt, a serious vascular wilt disease both in crops and wild species.The rate of in vitro multiplication by single node cuttings was used as a parameter of screening in two selection cycles with different concentrations of V. dahliae filtrate. One resistant clone was selected and then evaluated by inoculation in the growth chamber. Induced damage, and morphological traits (dry weight, leaf area and tuber production) were estimated. The selected clone was comparable to the resistant control, cv Kondor.The results suggest that genetic variation induced in tissue culture cound be utilized to generate disease resistance.     

The effect of varying the number of drills per plot and the amount of replication on the efficiency of potato yield trials

Summary The effect on yield trials of altering plot size was examined by investigating plots with varying numbers of drills (each with six tubers) planted. No evidence was found of the ware yield per drill being affected by different plot sizes nor any effect attributable to neighbouring drills, whether these were planted with another clone or left unplanted. Increasing the number of drills per plot did increase the precision of the estimated clone means as did, of course, increasing the number of replicates. It appeared, however, that increasing the number of replicates was a more efficient way to increase precision. Thus it was concluded that the most efficient utilization of limited planting space was to grow single drill plots with maximum replication.     

Chilean potato germplasm with resistance to potato viruses Y and S

Summary Four clones of the Chilota Potato Collection from the germplasm bank of the Universidad Austral de Chile, with potential combined resistance to PVX, PVY and PVS, were mechanically inoculated with these viruses in order to demonstrate wether they were truly resistant or not. Virus coat protein in the inoculated clones was determined by means of NCM-ELISA, DAS-ELISA, Western Blot and NASH.Two of the four inoculated clones were resistant to both PVY and PVS. This information will allow the utilization of these two clones in plant breeding programs.Abbreviations NCM-ELISA Nitrocellulose membrane enzyme-linked immunosorbent assay - DAS-ELISA double antibody sandwich enzyme-linked immunosorbent assay - NASH nucleic acid spot hybridization     

An assessment of morphogenic and transformation efficiency in a range of varieties of potato (Solanum tuberosum L.)

Summary To provide a truly genotype-independent transformation system, it is necessary to be able to transform a wide range of potato genotypes. The ability to regenerate shoots in vitro was determined for 34 potato varieties using tuber disc explants. Following a culture regime used extensively in previous studies with the variety Desiree, half of the varieties could be regenerated from tuber discs and half could not. From a sample of varieties that could be regenerated from tuber discs, all but one variety gave transgenic plants. Twelve varieties were evaluated for the capacity to regenerate shoots from leaf and internode explants excised from in vitro grown plants. All of the varieties tested regenerated adventitious shoots. Leaf and internode explants from 5 varieties were subsequently used for transformation, and transgenic plants were produced from two potato varieties that did not give transgenic plants from tuber disc explants. Some varieties could not be transformed by either method, and will require modification of the in vitro regeneration and transformation system to be successful.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid     

Female fertility of potato (Solanum tuberosum ssp. tuberosum) dihaploids

Summary Results of testcrosses and seed set data of the dihaploid breeding program at the Potato Research Institute in Gross Lüsewitz, Germany, indicate that the low level of female fertility could hinder success in crossing work. With the objective to reveal major components of female fertility, the behavior of 47 outstanding potato dihaploids (S. tuberosum ssp. tuberosum, 2n=2x=24) was assessed in testcrosses over a period of 3 years. Analysis of variance was carried out for the traits: number of seed per berry (S/B), number of intact seed per berry (IS/B), and number of non-germinable seed per berry (NGS/B). Significant sources of variation included cross combinations, years, and cross combination-year interactions. More than 20 S/B were obtained in 25.4% of all cross combinations performed over 3 years using up to three pollinators. Berry set was not correlated to seed set, but was in general determined by the pollinator used. The number of seedless berries (SLB/F) was related to neither total berry set nor seed production. The trait S/B remained stable over different years, and thus it deemed to be most useful as a measure of the level of female fertility in practical breeding work. Selection for female fertility in early generations of a breeding program is recommended to avoid limitations in the production of variability via sexual recombination.     

A comparison between single plant plots and five plant plots for the initial selection stage of a potato breeding programme

Summary The efficiency of single plant selection in the initial selection stage of a potato breeding programme was examined. A random sample of potato clones was grown in single plant plots and also in tworeplicates of five plant plots. After harvest, each plot was visually assessed by three potato breeders; total tuber weight and number of tubers per plant were also recorded, from which mean tuber weight was calculated. The error variances of the single plant plots were found to be significantly greater than from the five plant plots for total tuber weight, mean tuber weight and number of tubers per plant, but not significantly different for breeders' preference. Coefficients of correlation between single and five plants plots were significantly greater than zero for all traits examined, but they were lower than the corresponding correlations between the two replicates of five plant plots. Although a random sample of clones was examined, each clone had been assessed for breeders' preference the previous year. When the clones were grouped according to the previous years preference scores, it was found that the correlation coefficients between single and five plant plots for breeders' preference were inversely related, in magnitude, to the mean preference score of each group. It was concluded that single plant selection was generally ineffective, particularly when only the better clones, from the previous years assessment, are examined.     

Transgenic potato plants resistant to viruses

Summary Traditional potato breeding is a laborious process in which, by intercrossing, valuable traits from different parental clones are combined in a progeny genotype. Depending on the availability of genes, molecular techniques can be used to add specific genes to existing cultivars that, although otherwise satisfactory, lack a lew commercially important traits. For virus resistance the gene for the coat protein of a given virus transplanted into the genome of the plant renders the plant resistant to that virus. In conferring such resistance to potato varieties it proved to be possible to preserve their intrinsic properties.     

Chloroplast DNA variation in the wild potato species, Solanum acaule and S. albicans

The chloroplast DNA of Solanum acaule (109 accessions) and S. albicans (9 accessions) was investigated by restriction endonuclease analysis. Unexpectedly, all the accessions analyzed had C type chloroplast DNA in common. This suggested that S. acaule originated from a species with C type chloroplast DNA. DraI restriction digestion revealed further differentiation of C type chloroplast DNA into 8 types. The DraI polymorphism indicated the province of Salta in Argentina and the nearby regions to be a center of diversity for S. acaule. Surprisingly, S. albicans as well as S. acaule both ssp. acaule and ssp. punae, from Peru were virtually indistinguishable, although by morphology and/or cytology all three taxa are easily distinguished. This revised version was published online in July 2006 with corrections to the Cover Date.