Glycoalkaloid content in foliage of hybrid and backcross populations from aSolanum tuberosum X S. chacoense cross

The glycoalkaloid contents of foliage were measured in populations derived from a cross ofSolanum chacoense Bitter (PI 472810) with a composite sample of genotypes from a randomly matedSolanum tuberosum L. population. The mean total glycoalkaloid contents of the parent PI 472810 andtuberosum populations, and the F₂ and F₄ populations were 856, 121, 286, and 279 mg/100g fresh weight, respectively. The total glycoalkaloid content of the first backcross population, F₂ xtuberosum, was 290 mg/100 g, close to the content of the F₂. In a second backcross totuberosum, the mean total content was 148 mg/100 g, close to the content of the parenttuberosum population. Only the glycoalkaloids α-solanine and α-chaconine were found in PI 472810, whereas in the parenttuberosum, hybrid, and backcross populations, the glycoalkaloids α & β-solamarine also were found in a small number of genotypes. The ratios of chaconine to solanine contents were significantly (P≤.05) different in the parent PI 472810 andtuberosum populations, 2.55 and 2.12, respectively. The ratios in the F₂ and F₄ populations were similar to that of PI 472810, whereas the ratios in the backcross populations were closer to that of thetuberosum parent. The levels of foliage glycoalkaloids in the hybrid and backcross populations paralleled the levels of potato leafhopper,Empoasca fabae Harris, resistance measured in a previous study.     

Segregation of leptines and other glycoalkaloids inSolanum tuberosum (4x) ×S. chacoense (4x) crosses

A clone, 8380-1, selected fromSolanum chacoense (PI 458310) for its high foliage content of the leptine glycoalkaloids, a factor in resistance to Colorado potato beetle, was doubled in chromosome number from 2n=2x=24 to 2n=4x=48. Three 4x clones were crossed with sixS. tuberosum (4x) clones. Foliage glycoalkaloid contents were measured for 452 F1 hybrids from 15 crosses. The 4xchacoense parental clones were not different in respect to glycoalkaloid contents and were similar to the original 2x clone. All F1 hybrids synthesized foliage leptines ranging from 9 to 369 mg/100 g fresh weight (fw) with a mean content of 113 mg/100 g fw. The proportion of leptines in the total glycoalkaloid content ranged from 1% to 62% with a mean of 25%. The 4xchacoense parent mean leptine content was 1482 mg/ 100 g fw which was 90% of the total glycoalkaloid content. Tubers from 136 hybrids and the threechacoense parental clones were tested for glycoalkaloid contents. The tuber solanine + chaconine contents of the 136 hybrids ranged from 30 to 180 mg/100 g fw with a mean of 79. The mean tuber content of the threechacoense parental clones was 157 mg/100 g fw. Leptines were not found in any of the tubers.     

Leptines and other glycoalkaloids in tetraploidSolanum tuberosum xSolanum chacoense F2 Hybrid and Backcross Families

The leptine glycoalkaloids fromSolanum chacoense Bitter are potential resistance factors to Colorado potato beetle,Leptinotarsa decemlineata Say. A selected sample of 17 F₁ hybrids (4x) from crosses of a 4xS. chacoense clone that synthesizes leptines (8380-1) with 4xS. tuberosum L. lines were selfed to generate F₂ hybrids (4x) and were also backcrossed toS. tuberosum. Glycoalkaloid (GA) content in foliage and tubers was measured for 786 sibling genotypes from the two generations in the field at Beltsville, Maryland. Leptines were found in the foliage of all F₂ hybrids and in 98% of the backcross genotypes. Leptines were not detected in tubers from either generation. Foliage concentrations of leptines for the F₂ hybrids averaged 156 mg/100g fresh weight (FW). The proportion of the total GA content consisting of leptines averaged 42%. By backcrossing the F₁ hybrids toS. tuberosum the average concentration of leptines was reduced to 44 mg/100g FW. The proportion of leptines averaged 16%. The tuber contents of solanine plus chaconine glycoalkaloids averaged 52 mg/100g FW for the F₂ hybrids and 27 mg/100g for the backcross genotypes.     

Performance of populations derived by selecting for resistance to potato leafhopper in A 4XSolanum Tuberosum X 2XSolanum Chacoense cross

Intercross and backcross populations derived from aSolanum tuberosum L. (2n = 2x = 48) ×Solanum chacoense Bitt. (2n = 2x = 48) cross by selecting for resistance to potato leafhopper (PLH) (Empoasca fabae Harris), were tested in the field. In F2 and F4 populations, the levels of nymphal infestation and leaf necrosis from PLH feeding were considerably lower and tuber yields were much lower compared with those measured on the susceptible cultivar Kennebec. No differences were found between the two populations. Backcrosses of the F2 and F4 populations toS. tuberosum decreased resistance to PLH. Resistance to infestation was still greater than that of Kennebec; severity of leaf necrosis equaled that of Kennebec. Tuber yields increased, but were less than Kennebec’s yield. Foliage types shifted closer to those ofS. tuberosum. Three generations of selection and intercrossing within the backcross populations did not change the level of resistance to PLH but did tend to lower tuber yields. Foliage types remained primarilyS. tuberosum in appearance although distinctive types segregated with increased frequency. A second backcross toS. tuberosum did not change the level of resistance to PLH or the level of tuber yield relative to those of the first backcross or Kennebec.     

Glandular pubescence,glycoalkaloid composition,and resistance to the green peach aphid,potato leafhopper,and potato fleabeetle inSolanum berthaultii

Fifteen accessions ofSolarium berthaultii Hawkes andS. berthaultii xS. tarijense Hawkes were assessed for resistance to field infestations of the green peach aphid,Myzus persicae (Sulzer), potato leafhopper,Empoasca fabae (Harris), and potato fleabeetle,Epitrix cucumeris (Harris). Accessions bearing both Type A and Type B glandular trichomes were much more resistant to the green peach aphid and potato leafhopper than accessions bearing Type A hairs alone. All accessions had significantly smaller populations of these 3 pests than S.tuberosum cultivars. Total glycoalkaloid (TGA) content of foliage and tubers was not correlated with insect populations. Foliar TGA levels of field-grown plants varied among accessions, ranging from < 2–240 mg/100 g fresh wt. Solasonine and solamargine were the major foliar glycoalkaloids while solamarines predominated in tubers.     

Introgression and stabilization oferwinia tuber soft rot resistance into potato after somatic hybridization ofsolanum tuberosum ands. brevidens

Resistance to potato tuber soft rot caused byErwinia carotovora was transferred fromSolanum brevidens to the cultivated potato over the course of four backcross generations originating from a somatic hybrid. Soft rot reactions were determined via a tuber plug inoculation method developed during the course of these experiments. Soft rot resistance was highest in the somatic hybrid (only ca. 20% of tubers and plugs showed evidence of severe rotting) and lowest among progeny of control potato x potato crosses (ca. 80% of tuber plugs showed severe rot). Backcross generations involving somatic hybrids were intermediate in their reaction, and resistance stabilized to about 60% of tuber plugs showing severe rot in the BC₂ through the BC₄. Reciprocal crosses showed no difference in the inheritance of soft rot resistance, indicating that neitherS. brevidens norS. tuberosum donor cytoplasm had a significant effect on the expression of resistance. Crosses between BC₃ siblings where noS. brevidens genetic markers were detected but resistance was segregating demonstrated a dosage effect for soft rot resistance. We conclude that introgression of soft rot resistance has occurred and that at least one locus responsible for resistance inS. brevidens now resides in theS. tuberosum genome.     

Glycoalkaloid content inSolanum species and hybrids from a breeding program for resistance to late blight (Phytophthora infestans)

As part of an effort to study the relationship between the “glycoalkaloid trait” and genetic resistance to late blight (Phytophthora infestans), glycoalkaloid content in tuber and foliar tissues from a wide genetic background withinSolanum, includingS. demissum, S. iopetalum and 15 hybrids selected from a backcrossing breeding scheme was determined. Analysis of variance indicated significant genotypic effect on total glycoalkaloid, solanidine, α-solanine, and α-chaconine content in both tubers and leaves. Tubers from wild potato species commonly contain glycoalkaloids in concentrations that exceed international health regulations for human consumption (20 mg/100 g fresh weight). In this study,S. demissum andS. iopetalum were highest in total tuber glycoalkaloids among all materials tested, with 70.4 and 76.2 mg/100 g fresh weight, respectively. In contrast, both commercial cultivars had the lowest concentration, both below the safety limit. Solanine was more abundant than chaconine in all but one genotype. All hybrids were intermediate to low in total glycoalkaloids. Except for the two wild species, glycoalkaloid concentration in leaves of all genotypes studied was at least twice that in tubers, with glycosylated forms accounting for more than 80% total glycoalkaloid content. Correlation between tuber and foliage alkaloids was poor. In view of the observed field resistance to late blight, it was concluded that tuber glycoalkaloid content may not be responsible for such resistance.     

Glycoalkaloids and resistance to the Colorado potato beetle inSolanum chacoense Bitter

Resistance of 20 F₂ Solarium chacoense Bitter clones to the Colorado potato beetle,Leptinotarsa decemlineata (Say), was measured in a field test. Levels of total glycoalkaloids (TGA) and composición of the glycoalkaloid mixtures in foliage of the clones were also determined. Clones with either commersonine or dehydrocommersonine as the major foliar glycoalkaloid were significantly more resistant (lower damage ratings, fewer larvae and adult insects) than clones with solanine and chaconine. Damage ratings were negatively correlated (r = -0.67, p = 0.01) with foliar TGA levels. The results indicate that the types of glycoalkaloids present in the foliage ofS. chacoense may be as important as the level of TGA in limiting damage and numbers of insects.     

Change in Some Glycoalkaloids of Potato under Different Storage Regimes

The potato (Solanum tuberosum L.) is an important food crop worldwide. Potato tubers can be stored to provide continuity of supply between production seasons, but it is important that they be stored under appropriate conditions as incorrect storage will result in deterioration in end user quality and may increase glycoalkaloid levels. We have investigated the effects of types of household storage on potato glycoalkaloid content (total glycoalkaloids [TGA]; α-solanine; α-chaconine) in Turkey. Tubers of potato cultivars (cvs.) Agria and Bettina were stored under four types of storage conditions (indirect sunlight for 10 h per day and dark storage for the remaining 14 h per day; storage under continuous fluorescent light; storage in constant darkness; storage in the dark in a refrigerator) for 56 days. Samples of tubers were taken at the beginning of the storage period and after 14, 28 and 56 days of storage for tuber glycoalkaloid measurement. Tubers stored in the three light environments showed an increase in glycoalkaloid levels; however, none of the cv. Agria tubers reached the critical level of 200 mg/kg tuber. On day 56 the TGA level of cv. Bettina tubers stored under fluorescent light reached 234.31 mg/kg.     

Evaluation for chipping and tuber soft rot (Erwinia carotovora) resistance in potato clones from unilateral sexual polyploidization (2x × 4x)

The aim of this work is the evaluation of tetraploid potato clones with germplasm fromS. chacoense andS. phureja for chipping and resistance to tuber soft rot (Erwinia carotovora subsp.carotovora). Tetraploid potato clones were obtained via 2n eggs through 2x–4x crosses. Cytological mechanisms were investigated in the diploid hybrid 2n-egg producer used as parent in the unilateral sexual polyploidization scheme; the omission of the second meiotic division and cytokinesis failure at the end of meiosis were identified with a genetic consequence equivalent to second division restitution (SDR). Tuber marketable yield, specific gravity and chip-processing ability evaluated at harvest and after cold storage with and without reconditioning were higher in some clones as compared to theS. tuberosum tetraploid parent. Tuber soft rot resistance, contributed byS. chacoense, was successfully transferred to the4x level. After inoculation withErwinia carotovora subsp.carotovora and estimation of the rotted area, one tetraploid clone proved to be resistant and three partially resistant. The genetic value of exotic germplasm and sexual polyploidization strategy are discussed in relation to potato improvement.     

Ascorbic acid and glycoalkaloid content of Atlantic and Superior potato tubers as affected by supplemental irrigation and soil amendments

Atlantic and Superior potato (Solanum tuberosum L.) tubers were collected at harvest from two field experiments in Maine during 1993 and 1994. Tubers were analyzed for ascorbic acid (ASC) and total glycoalkaloid (TGA) concentration within one month of harvest and after 4 to 5 months of storage at 10 C. ASC concentration was significantly higher in Superior than Atlantic at harvest and after storage. TGA concentration was consistently higher in Atlantic than Superior. Irrigation tended to slightly reduce ASC and increase α-solanine concentrations when applied too late in the season for yield benefits. Storage decreased tuber ASC content, but no specific pattern was observed for TGA changes. Soil amendment programs using compost and manure (22 Mg ha^?1 potato compost + 45 Mg ha^?1 manure) did not dramatically affect tuber ASC or TGA concentrations. ASC content of the tubers declined dramatically in storage, but no consistent pattern was found for tuber TGA changes. We conclude that genotype, growing environment, and storage time play much stronger roles in determining tuber ASC and TGA levels than do irrigation and soil management programs. We observed a negative relationship between the average tuber size of the assayed samples and ASC concentration in fall samplings; however, this relationship was not observed from storage. Average tuber size and TGA content generally displayed a negative relationship.     

Tuber quality and soft rot resistance of hybrids betweenSolarium tuberosum and the incongruent wild relativeS. commersonii

Tetraploid BC₃ hybrids between sexually incompatible speciesSolanum commersonii andS. tuberosum were characterized for tuber quality (stolon length, tuber eye depth, chipping color from 3-month storage at 5 C, and specific gravity) and soft rot resistance traits. For all analysed morphological traits, except stolon length, genotypes resembled theS. tuberosum phenotype. On average, the specific gravity of selected genotypes was quite high (1.087), and 12 of them had a value >1.090. As for chipprocessing ability, 4.8% of genotypes chipped well directly from cold storage, and 14.3% after reconditioning. All but one of these genotypes also possessed a high specific gravity of tubers. Variability was found for resistance toErwinia carotovora subsp.carotovora. In particular, 24% of hybrids had a rotted area diameter ≤ 4 mm and were classified as resistant. The average percentage ofcommersonii-specific markers still present in the BC₃ hybrids was 22%, ranging from 9% to 37%. Genotypes combining good qualitative tuber traits with a wild genome content lower than the average value of the population were selected for further breeding efforts. The importance of molecular-assisted selection is discussed.     

Foliar leptine production in segregating F1, Inter-F1, and backcross families ofSolanum chacoense bitter

Levels of foliar leptine glycoalkaloids were measured in segregating F₁, inter-F₁, and backcross families derived fromS. chacoense (PI 320287) sibs 55-1 and 55-3, which axe (respectively) high and nil leptine producers, and from crosses of these two genotypes with 8380-1, which produces high levels of leptine, to study the inheritance of leptine biosynthesis inS. chacoense. A total of five F₁ families was produced from reciprocal crosses between 55-3 and 55-1 and between 8380-1 and 55-3, and from the cross 8380-1 x 55-1. The F₁ crosses produced two leptine classes, high (≥62% of total glycoalkaloids; TGA) and low (≤17% of TGA). Twenty-three families were derived from F₁ intercrosses and backcrosses of high x high, low x low, high x low, and low x high F₁ individnals. These families produced all high, all low, or both high and low leptine classes, depending upon type of cross. Three of the reciprocal (high x low) F₁ families segregated 1:1 for high:low leptine, and progeny from the (high x high) 8380-1 x 55-1 cross were all high, consistent with control by a single recessive gene in this population. One of the reciprocal families (9501) differed slightly but significantly (p=0.05) from 1:1. All of the low x high and high x high inter-F₁ and backcross families segregated as expected based on a single recessive gene model; however, five of eight high x low and four of six low x low families differed significantly from expectation, suggesting the presence of additional factors affecting the inheritance and expression of leptine glycoalkaloids in this population orS. chacoense.     

Horizontal resistance insolanum tuberosum to colorado potato beetle (leptinotarsa decemlineata say)

Horizontal resistance (HR) was assessed as a strategy to reduce potato defoliation by the Colorado potato beetle (CPB). Hybrids amongSolanum tuberosum varieties grown in Iowa were first evaluated with a detached leaflet feeding bioassay. Beginning in 1998, resistance was increased annually over three years by intermating and selecting the most resistant l%–2% of each generation of 300–400 plants using the bioassay. When C (= mg leaf tissue consumed_* neonate larva^-1 over 48 h) was measured for the 1% most-resistant genotypes of all generations grown side by side in 2000, it ranged from 6.1 mg_* larva^-1 in the parents to 2.3 for progeny of the F₃ generation compared to 2.7 in ND2858-1, a resistant check. Field trials in Wisconsin showed less defoliation in the F₁ and F₂ selected genotypes than in the parents. A second breeding program using moreS. tuberosum parents with greater genetic diversity, and much larger breeding populations, resulted in significantly faster accumulation of resistance, further suggesting that recurrent mass selection is effective. Foliar glycoalkaloid analyses revealed low levels of solanine and chaconine in the F₃ selections; no leptines or leptinines were detected. Because the parents wereS. tuberosum varieties in which vertical resistance to CPB is unknown, and because the resistance to feeding from parents to the F₃ resistant plants was linear and gradual while ranging from initially very low to considerably higher in the third year, horizontal resistance is strongly implicated. The development of a significant degree of resistance after three rounds of breeding using relatively small breeding populations suggests that HR can be developed from varieties ofSolanum tuberosum lacking initial high levels of resistance to CPB.     

Pollen-pistil incompatibility in a diploid hybrid potato population with cultivated and wild germplasm

The basis of low seed set was investigated in a diploid hybrid population with germplasm from the cultivated speciesSolanum tuberosum spp.tuberosum andS. tuberosum ssp.phureja and the wild speciesS. chacoense. Controlled crosses were performed following an incomplete diallel mating design which included the hybrid population and the parental species. Pollen grain germination and pollen tube growth were observed with fluorescence microscopy in 174 intrapopulation and interspecific combinations of genotypes. Fifty percent of the combinations of genotypes within the hybrid population and 46% of those between this population and the parental species were incompatible; overall, 71% of the interspecific combinations of genotypes were compatible when plants of the hybrid population were used as females, vs. 5% when used as males. Although the site of reaction could vary in a given intrapopulation or interspecific cross with the combinations of genotypes, pollen tube inhibition occurred in the first third of the style in 42% of them. Since the gene pool of the hybrid population had been widened with germplasm from other geographic areas and the genotypes ofS. tuberosum ssp.tuberosum, S. chacoense andS. tuberosum ssp.phureja used in this study were not the ones involved in the original crosses, it is concluded that the S-locus is not controlling the incompatibility reaction but rather that a cross-incompatibility system, possibly governed by more than one locus, is acting.     

Photoinduction of glycoalkaloids in cured potatoes

Curing of Sebago potatoes for 10 days at 25°C prior to common storage at 5°C, reduced the responsiveness of tubers to photoinduced glycoalkaloid synthesis. Continuous illumination with 15 and 25-Watt incandescent light for 10 days increased glycoalkaloid content of peelings (12–14% of tuber weight) in uncured potatoes by a factor of 3.2 and 2.8, respectively, while the corresponding factor for cured tubers was only 1.8 for both lights. The peeled tuber portion (86–88% of tuber weight) had negligible amounts of glycoalkaloids, averaging about 1 mg per 100 g of fresh weight. The rise of glycoalkaloid levels in peels of uncured tubers was nearly linear to 164.7 mg/100g (15W light) with no indication of levelling off. In peels of cured tubers, the rise began only after the 4th day of light exposure with an apparent maximum and levelling off at 94.7 mg or approximately 43% lower than the final TGA levels in uncured tubers.     

Evaluation of wild tuber-bearingSolanum accessions for foliar glycoalkaloid level and composition

Six hundred forty-five accessions of 70Solanum species and six natural hybrids were screened for foliar glycoalkaloids. Total foliar glycoalkaloid (TFGA) level and glycoalkaloid composition of one or more accessions of each species were determined by TLC and GLC analyses. Of the more than 12 different glycoalkaloids found in the wild species in this survey, solanine and chaconine account for more than 60% of the TFGA found in the foliage of these plants. There was wide variation in the total glycoalkaloid levels among the species.S. neocardenasii had the highest average TFGA value of the 70 species, 222 mg/100 g fresh wt (222 mg %) and an accession ofS. chacoense had the highest TFGA value recorded in the survey, 486 mg %. Of the 70 species, only 11 had average TFGA levels of more than 100 mg %. However, one or more accessions in 27 of the species synthesized more than 100 mg %. Forty-five species synthesized an average level of less than 50 mg %. The level usually found in the foliage of commercial potato cultivars is about 50 mg %. Therefore, most of theSolanum species in the potato germplasm collection can be considered low glycoalkaloid species.     

Selection of monoploids for protoplast fusion and generation of intermonoploid somatic hybrids of potato

The union of potato monoploid genotypes (2n=1x =12) through protoplast fusion may result in vigorous somatic hybrids due to a reduction of the “genetic load” normally present in this highly heterozygous tetraploid (2n=4x=48) crop. More than 100 androgenic monoploids derived from diploid (2n=2x=24)Solanum phureja Juz. & Buk. andS. chacoense Bitt. xS. phureja clones were evaluated in field trials during 1996 and 1997 to identify the most promising genotypes for protoplast fusion experiments. Compared to the total population, the 1996 selected genotypes had higher means for tuber number (30.1 vs 11.2 tubers/plant), average tuber weight (3.0 vs 1.8 g/tuber) and total yield (66.1 vs 20.4 g/plant). Similarly, the 1997 selected genotypes had higher means for tuber number (42.8 vs 25.4 tubers/plant), average tuber weight (3.6 vs 2.5 g/tuber) and total yield (114.0 vs 63.4 g/plant) compared to the total population. The 31 selected monoploid genotypes from 1996-97 varied in their response to protoplast isolation and culture from no growth (9), cell enlargement (5), limited cellular divisions (8), callus formation (5) to plant regeneration from callus (4). Chemical fusion and electrofusion produced three groups of intermonoploid somatic hybrids. Polymorphic simple sequence repeat (SSR) loci enabled distinction of somatic hybrids from parental somaclones. Rapid DNA extraction with SSR analysis enabled screening of calluses to identify somatic hybrid tissue prior to plant regeneration. The somatic hybrids were highly polyploid, mostly hexaploid (2n=6x=72), possibly due to fusion of endopolyploid protoplasts and/or chromosomal doubling during plant regeneration.     

Aneuploid hybrids from 5x − 4x crosses in potato: Chromosome number, fertility, morphology and yield

The objective of this study was to characterize sixS. commersonii - S. tuberosum progenies deriving from 5x ? 4x crosses to provide evidence that they can be used in potato breeding. Hybrids analyzed (coded PTH) had a chromosome number between the 4x and the 5x level. In particular, progeny means for chromosome number ranged from 50±0.5 to 54±0.7, with most (70%) genotypes exhibiting a low aneuploid level of 48 to 53 chromosomes. Despite being aneuploid, the hybrids did not generally show phenotypic aberrations or vigor reduction common to aneuploids of other species. Most genotypes resembledS. tuberosum in growth habit, whereas corolla type, eye depth, and stolon length varied between and within progenies. Aneuploid hybrids produced tubers under long-day conditions. However, tuber yields were not as high as expected, probably due to lack of adaptation of theS. commersonii genome to long-day conditions. Although aneuploidy has often been associated with reduced male and female fertility, many 5x ? 4x hybrids were fertile in crosses withS. tuberosum. The average berry set and number of seeds/berry were 33% and 34.7, respectively, following PTH ×S. tuberosum crosses, and 40% and 51.7, respectively, forS. tuberosum × PTH crosses. The useful variation for fertility and tuber traits found in this material is being used for further breeding efforts.     

Erwinia resistance in backcross progenies ofSolanum tuberosum x S. tarijense andS. tuberosum (+) S. commersonii hybrids

Summary The resistance to tuber soft rot caused byErwinia carotovora ofSolanum tuberosum x S. tarijense andS. tuberosum (+) S. commersonii hybrids and their backcrosses is reported. A number of resistant diploid sexual hybrids and tetraploid/hexaploid somatic hybrids were selected. Backcross progenies were obtained through 2x×4x crosses involving a resistant diploid hybrid and tetraploidS. tuberosum, and through 4x×4x crosses between a resistant somatic hybrid andS. tuberosum. The hybrids showed high variability interms of resistance to tuber soft rot. The resistance of progeny from 2x×4x backcrosses was similar to that of the parental sexual hybrid. By contrast, the resistance of genotypes deriving from 4x×4x backcrosses was reduced compared with the resistant somatic hybrid. In general, tuber characteristics of the backcross hybrids improved considerably as compared with their parents, and tuber yield per plant was good.