Preventing chimerism in potato (Solanum tuberosum L.)

Summary A fast neutron irradiation experiment using two different dose rates has been performed on the potato variety Desiree in order to obtain chimera-free mutants. Both tubers and tuber parts (cross sections) were de-eyed at different moments before and after irradiation. Adventitious sprouts successively developing on the callus in the holes of excised eyes were separated from the treated tubers and planted individually. So called grouped sprouts were separated. Results indicated that (practically) chimera-free mutants can be obtained by de-eying tuber parts shortly before irradiation, by applying relatively high dose-rates and by taking adventitious sprouts which develop not earlier than three months after irradiation.Separation of the grouped sprouts demonstrated that each part originated from a single original cell.This article is dedicated to Dr F. P. Ferwerda who till September 1969 was in charge of potato mutation research at our Institute.     

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.     

Identification of the trisomic series in diploid Solanum tuberosum L. group Tuberosum. II. Trivalent configurations at pachytene stage

Summary By means of pachytene analysis 11 of the 12 possible types of primary trisomics of diploid S. tuberosum have been identified. The typical trivalent configurations for each chromosome are illustrated. Triplo-4,5,7 and 9 occurred more frequently whereas triplo-1 is still lacking in the series. Some of the features of trivalent associations at pachytene are discussed, as also the fact that in the present study only primary trisomics have been found.     

Association mapping of quality traits in potato (Solanum tuberosum L.)

In this paper, we describe the assessment of linkage disequilibrium and its decay in a collection of potato cultivars. In addition, we report on a simple regression based association mapping approach and its results to quality traits in potato. We selected 221 tetraploid potato cultivars and progenitor lines, representing the global diversity in potato, with emphasis on genetic variation for agro-morphological and quality traits. Phenotypic data for these agro-morphological and quality traits were obtained from recent trials performed by five breeding companies. The collection was genotyped with 250 AFLP^® markers from five primer combinations. The genetic position of a subset of the markers could be inferred from an ultra dense potato map. Decay of linkage disequilibrium was estimated by calculating the squared correlation between pairs of markers using marker band intensities. Marker-trait associations were investigated by fitting single marker regression models for phenotypic traits on marker band intensities with and without correction for population structure. The paper illustrates the potential of association mapping in tetraploid potato, because existing phenotypic data, a modest number of AFLP markers, and a relatively simple statistical analysis, allowed identifying interesting associations.     

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

Summary 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.Scientific Journal Series Article 14896 of the Minnesota Agricultural Experiment Station supported in part by the U.S. Agency for International Development, contract no. 608-0160, IAV Morocco Project.     

Genetic analyses for bioactive potential in tetraploid potato (Solanum tuberosum L.)

A total of four traits related to bioactive potential of the tetraploid potato were studied in a North Carolina II cross‐experiment. The objectives of this study were to estimate genetic parameters for target bioactive compounds in a tetraploid potato population, to determine phenotypic and genotypic correlations and to calculate combining ability effects of cultivars and breeding lines included in the crossing scheme. Total monomeric anthocyanins, phenolics, carotenoids and hydrophilic antioxidant capacity were measured by spectrophotometric methods. The sources of variation female (GCA_f), male (GCA_m) and their interaction (SCA) were significant for bioactive compounds and antioxidant capacity. Narrow‐sense heritability estimates (h²) were moderate for all the traits (0.413–0.657). Both phenotypic and genotypic correlations were highly significant for phenolic compounds and antioxidant capacity. As regards combining ability, positive and negative GCA and also SCA effects have been identified for bioactive compounds and antioxidant capacity. These results indicate that hybrid breeding lines can be obtained by choosing parents with significant GCA, whose bioactive potential can also be further enhanced if the crosses have a significant SCA.     

Identification of the trisomic series in diploid Solanum tuberosum L., group tuberosum. I. Chromosome identification

Summary The morphology of 12 pachytene bivalents of the dihaploid Solanum tuberosum cv. Gineke is described, and the morphological features which are helpful for a critical chromosome identification are illustrated. The difficulties of identifying the individual chromosomes and the extra chromosomes in trisomics are discussed.     

Introduction of an amylose-free (amf) mutant into breeding of cultivated potato,Solanum tuberosum L.

Summary Using an amylose-free (amf)mutant of diploid potato (Solanum tuberosum), diploid and tetraploid clones with different genotypes at the amf-locus were produced. In order to make use of the diploid material in analytic breeding of amf-potatoes, clones were selected that produced a considerable frequencies of 2n-pollen and 2n-eggs. Successful attempts were made to select normal synaptic as well as desynaptic clones producing 2n-gametes. Based on the phenotype of starch in the microspores, tetraploid clones with nulliplex, simplex and duplex genotypes at the amf-locus were selected. Prospects of using this material in conventional as well as in analytic breeding of potato are discussed.     

Some more evidence of autotetraploid inheritance in the potato (Solanum tuberosum)

1. 1.
   The results presented here support the assumption that the potato species Solanum tuberosum is a true autotetraploid.     
   
   

Evaluation of seedling selection for salinity tolerance in potato (Solanum tuberosum L.)

Summary Salt-tolerance in potato (Solanum tuberosum L.) was selected on the basis of germination and survival of seed sown in trays of perlite suspended in either 75 or 150 mM NaCl. Salinity reduced the germination of seed. Genetic differences in salt-tolerance were apparent with salt reducing germination more in seed collected from cv. Cara than in that collected from cv. Maris Piper. Progeny from the seedling selection were then grown to maturity to produce tubers.The relative tolerance of the parental cultivars and of unselected and selected progeny to long-term exposure to salinity was examined in a pot experiment in which plants were irrigated with either fresh water or 50 mM NaCl solution from one week after plant emergence. In this experiment, salinity significantly reduced leaf conductance, total dry matter production and partitioning of assimilate to tubers. Salinity reduced dry matter production and assimilate partitioning to tubers to a greater extent in Cara than in M. Piper. Progeny selected for short-term salt-tolerance did not exhibit greater long-term salt-tolerance than unselected progeny, and both were more sensitive than M. Piper.These results demonstrate genetic variation in salt-tolerance in potato. However, although there was a correlation between the performance of the parent to long-term salinity and survival of progeny in the seedling selection, there was no correlation between short- and long-term salt-tolerance. This suggests that characters underlying short-term tolerance may contribute to long-term tolerance but do not of themselves confer long-term tolerance. Future progress in selecting for improved salt-tolerance depends on understanding the effects of salinity on the physiological processes underlying growth and carbon partitioning.     

Production of haploids of potato (Solanum tuberosum subsp. tuberosum) and their identification with electrophoretic analysis

Summary The frequency of haploid production following the interspecific pollination of eight tetraploid potato cultivars (Solanum tuberosum subsp. tuberosum) with Solanum phureja clone 1.22 was investigated. A total of 185 haploids were produced with an overall haploid frequency of 3.9 haploids/100 fruits. The haploid frequency was affected by the genotype of the maternal parent. Atlantic, ND860-2, Superior, Saginaw Gold, Spartan Pearl, Nooksack and Onaway had frequencies of 6.2, 5.1, 4.7, 3.9, 2.3 and 0.7 haploids/100 fruits, respectively. There were 60 and 57 haploids produced from Atlantic and Saginaw Gold, respectively, and no haploids were extracted from fruits of Lemhi Russet. Isozyme analysis and visual examination were performed independently to compare the efficiency of discriminating hybrids from haploids. Approximately 80% of total hybrids could be identified by electrophoretic analysis, while 77% were distinguished through visual examination. Pgm-2 ¹, which is unique in the clone 1.22 and absent from all seed parents, was found to be the most useful locus in hybrid identification and 50% of total hybrids could be distinguished by this allele. With similar rationale, Mdh-1 ¹ allozyme, which was absent in six of the eight parents, identified 37% of total hybrids. A combination of both visual and electrophoretic methods made hybrid identification even more efficient, with an average identification efficiency of 91%. A scheme was proposed to develop a new haploid inducer which would be homozygous for both Pgm-2 ¹ and embryo spot.     

Meiosis in triploid Solanum tuberosum L.

Summary Meiosis in triploid Solanum tuberosum was studied in plants that originated from crosses between tetraploids and diploids, the latter being mainly dihaploids.Association of chromosomes in first metaphase was regular, being as expected for autotriploid material. In first anaphase lagging chromosomes occurred that mostly divided precociously into their chromatids, the amount of lagging chromosomes being more or less proportional to the average number of univalents at M I. The A I distribution of chromosomes over the poles fitted a normal distribution.In the second meiotic division also lagging chromosomes were observed. During this division disturbances occurred resulting in cells with more or less the somatic chromosome number. The origin of this aberration is discussed, together with the relation between meiotic behaviour and pollen stainability.     

Integration of transgenes into sexual polyploidization schemes for potato (Solanum tuberosum L.)

Most potato transgenic research has focused on development of resistance to pathogens and modification of potato physiology. Many transgenes, particularly those conferring pathogen resistance, could substantially lower potato production costs in developing countries. However, transgenes have not been reported in sexually propagated 4x-2x potato hybrids commonly grown in developing countries. Two transgenes,the Bacillus thuringiensis cry3Aa endotoxin protein gene and the PVY°coat protein gene, were engineered intodiploid and tetraploid potato using Agrobacterium tumefaciens-mediated transformation. Cry3Aa was produced at high levels in several lines while the PVY° coat protein was not expressed. Diplandroid and tetraploid genotypes were crossed to produce transgenic 4x-2x hybrids. Genetic transformation had no discernable effect on fertility ofthe primary transformants, germination of4x-2x seed derived from the transformants and agronomic performance(tuber set, average tuber weight and total tuber yield) of the 4x-2xhybrids. The transgenic 4x-2xhybrids produced non-viable pollen and could only be crossed as female parents. Results suggest that transgenes, such ascry3Aa, could be expressed in 4x-2x hybrids to lower costs of production with no significant effect on plant phenotype. This revised version was published online in July 2006 with corrections to the Cover Date.     

Anther culture of Solanum tuberosum L.

Summary Embryoid formation was induced in pollen of Solanum tuberosum, cv. Pentland Crown, Maris Piper and Record, by culturing anthers at or just prior to the first pollen mitosis. The composition of the medium was not critical in respect of either nutrients or hormones. In the presence of relatively high hormone levels, callus formation also occurred from somatic tissues of the anthers.     

Parthenogenetic monohaploids (2n=x=12) from Solanum tuberosum L. and S. verrucosum Schlechtd. and the production of homozygous potato diploids

Summary Dihaploid and dihaploid derived clones of Solanum tuberosum and diploid genotypes of S. verrucosum produced 85 viable monohaploids by female parthenogenesis. All were induced using diploid S. phureja clones, homozygous for embryo spot, as pollinator. Frequency of S. tuberosum monohaploids per 100 berries was rather constant in three successive years (14, 17 and 17 respectively). No male and female fertility was found in flowering monohaploids.Colchicine-induced chromosome doubling yielded homozygous s. tuberosum diploids with low pollen quality but good seed fertility.Two diploid self-incompatible species (S. multidissectum and S. berthaultii) produced no monohaploids. The presence of genes for female parthenogenesis in some dihaploids is discussed.     

Genetics of self-compatibility in dihaploids of Solanum tuberosum L. 5. The S-genotype of tetraploid potato cultivar gineke

Summary Investigations of the genetics of self-compatibility and self-incompatibility in dihaploids and diploid derivatives from cv. Gineke revealed the presence of S ₁, S₂ and S ₃ at the S-locus of Gineke and in addition an S ₁-allele on a translocation. By means of a complete tester set involving the S-alleles S ₁, S₂ and S ₃ (all from Gineke) and S ₄ (from Black 4495) it was demonstrated that some Gineke dihaploids were compatible with all six testers. This indicated a fourth S-allele in Gineke, which differs from those in the tester series and was therefore assigned S ₅. Additional evidence was obtained from an analysis of F₁'s from crosses of two S ₅-bearing dihaploids and one of the testers. So the S-genotype of cv. Gineke was identified as S ₁S₂S₃S₅/S₁, the second S ₁ being the S-allele on a translocated fragment.     

Induction of fertile flowers in potato (Solanum tuberosum L.) by silver thiosulphate anionic complex

Summary The effect of gibberellic acid containing mixtures, silver thiosulphate and extended photoperiod on flowering induction in 16 non-flowering potato genotypes and on flowering enhancement in 14 normally potato flowering genotypes was studied in sub-tropical plains of India during short-day autumn crop season of 2000–2001 and 2001–2002. Extended photoperiod alone was not successful in induction of flowering. Silver thiosulphate in combination with extended photoperiod effectively induced flowering in 16 potato genotypes studied for flowering induction. Induced flowers of some genotypes were male fertile. Normal berry setting was observed on induced flowers and seeds obtained from such berries germinated normally. Gibberellic acid containing treatments were not very effective in flower induction as they induced some flowering only in few genotypes. In the normally flowering genotypes silver thiosulphate enhanced maximum flowering and duration of flowering to a great extent.     

Identification of epistatic interaction affecting glycoalkaloid content in tubers of tetraploid potato (Solanum tuberosum L.)

Glycoalkaloids are secondary metabolites characterised by an undesirable taste, and known to be toxic when consumed in large quantities. Their content in potato tubers should therefore be selected against and DNA markers can significantly facilitate such a process. This study was designed to describe the genetic control of the total content of glycoalkaloids (TGA) in the potato tuber and to enhance the development of DNA markers. A segregating population was constructed from tetraploid potatoclones, which were characterised by divergent TGA-content. The population had a high-TGA parent, LT7, and a low-TGA parent, NT8. We used 342 Inter-Simple Sequence Repeat (ISSR) single primers or two such primer combinations and 36 Cleaved Amplified Polymorphic Sequence (CAPS)primer pairs, digested with various restriction enzymes, to amplify random PCR products. Parental clones of both populations were used to identify polymorphic PCR products for further linkage analyses with TGA-content. In these analyses, one single ISSR marker was found to be significantly associated with TGA-content. A multiple regression analysis was also carried out using a ‘stepwise’ procedure. In this regression analysis TGA-content was the dependent variable whereas the polymorphic PCR products and all possible two-way interactions among them were the independent variables. The resulting best model consisted of an interaction between two loci in addition to a single locus effect. This interaction suggests that the expression of TGA-content is partially modulated by two interacting loci. This revised version was published online in July 2006 with corrections to the Cover Date.     

Transfer of resistance to Verticillium dahliae Kleb. from Solanum torvum S.W. into potato (Solanum tuberosum L.) by protoplast electrofusion

Summary Interspecific somatic hybrid plants were regenerated after electrofusion of mesophyll protoplasts with the objective of transferring resistance to Verticillium dahliae from Solanum torvum into potato. Early selection of the putative hybrids was based on differences in cultural behaviour of the parental and hybrid calli (particularly the ability of the latter to regenerate early) in combination with morphological markers. Four putative hybrids were recovered from hundreds of calli, probably resulting from complementation of the two parental genomes. The regenerates were tetraploids (2n=4×=48 chromosomes) and exhibited intermediate traits including leaf form, plant morphology and the presence of anthocyanin. The hybrid nature of the four selected plants was confirmed by examining isoenzyme patterns for isocitrate dehydrogenase (Idh), malate dehydrogenase (Mdh), phosphoglucoisomerase (Pgi) and 6-phosphogluconate dehydrogenase (6-Pgd). While the hybrid plants rooted readily and grew vigorously under in vitro conditions, in the greenhouse their development and growth were retarded by difficulties in rooting. When grafted on potato or S. torvum rootstocks, the hybrid plants recovered normal development and growth. Again, they exhibited intermediate morphological traits. Tests for resistance realized in vitro with medium containing 50% Verticillium wilt filtrate showed that all the somatic hybrids were resistant to the fungus filtrate.     

Divergent strategies displayed by potato (Solanum tuberosum L.) cultivars to cope with soil drought

The physiological responses of potato (Solanum tuberosum L) cultivars to soil drought at the tuberization phase and their impact on agronomically important traits were investigated in potted plants under semi‐controlled conditions. Genotype‐dependent responses of potato to water deficiency were evaluated on two pairs (tolerant/sensitive) of Polish cultivars. Each pair of cultivars had a similar genetic background but was extremely different in terms of drought tolerance evaluated on the basis of loss of tuber yield under field conditions. The results clearly indicate different mechanisms of tolerance to water deficiency and the ability to recover from soil drought in two tolerant but genetically unrelated cultivars. When subjected to soil drought, the cultivar Gwiazda had low rates of transpiration and photosynthesis and low levels of stomatal conductance due to hypersensitivity to ABA, but its maximal photochemistry efficiency and PSII performance index were unchanged. Another strategy was displayed by the dehydration‐avoidant cultivar Tajfun, which kept the stomata partially open. Thus, the plants were able to retain a relatively high rate of photosynthesis over transpiration. The parameters measured for cultivar Tajfun for photosynthesis and transpiration were the same after plant rewatering, similar to the control plants. This was not the case for the cultivar Gwiazda. The ability of plants to regenerate after soil drought relief appears to be a good indicator of potato susceptibility to soil drought and allows the yield of potato tubers to be predicted. The physiological traits identified in closely related potato cultivars but differed in their drought tolerance seem to be useful for genetic engineering and breeding programmes.