Inheritance of potato glycoalkaloids

Significant differences in tuber glycoalkaloid (TGA) content were found among parents and among family means in a two year study of 10 tetraploid crosses. TGA contents of the parents ranged from 3.6–36 mg/100 g, with an average content of 10 mg/100 g. Offspring variations within families were generally continuous, indicating polygenic inheritance. Heritability (1-year—1-replicate base) ranged from 86–89% in the broad sense and from 66–84% in the narrow sense. It was concluded that TGA content is highly heritable. The use of parents with high TGA contents in a breeding program is discussed.     

Genetic and environmental control of potato glycoalkaloids

Genetic and environmental factors that can cause potato tubers and processed products to have excessive glycoalkaloid levels (> 20 mg/100 g fresh wt) are reviewed and discussed. Measures that breeders, growers, processors, and distributors might take to maintain glycoalkaloid levels at their present low levels are suggested.     

Preparative isolation ofSolanum tuberosum L. glycoalkaloids by MPLC

Summary A new, efficient and economic method employing Medium Pressure Liquid Chromatography (MPLC) for the isolation of the two majorSolanum tuberosum L. glycoalkaloids (α-solanine and α-chaconine) is described. Potato peelings are homogenised with 5% acetic acid, the glycoalkaloids purified by filtration through an XAD-2 column and then by precipitation from the aqueous solution. The resulting glycoalkaloid fraction was purified by MPLC using a Silica Gel column and a CHCl₃:MeOH:2% NH₄OH mixture (70∶30∶5) as mobile phase to yield pure α-chaconine and a-solanine. This methodology can be used to obtain glycoalkaloids for enthomology and toxicological research where large amounts of these compounds are required.     

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.     

A rapid method for the quantification of steroidal glycoalkaloids by reversed phase HPLC

Summary Methods were developed for clean-up of potato tuber extracts on solid phase extraction CN-cartridges and for analysis of steroidal glycoalkaloids by reversed phase HPLC. The alkaloids α-solanine, α-chaconine, α-solasonine and α-solamargine could be separated on C₈ or C₁₈ reversed phase columns using a mobile phase of acetonitrile/Tris-buffer (3∶2, v/v). The analysis time of tuber extracts containing these alkaloids was less then 4 min, if the pH of the mobile phase was adjusted to 7.4 and run at a flow rate of 0.5 ml/min.     

Steroid glycoalkaloids and related compounds as potato quality factors

The steroid glycoalkaloids are triterpenoid derivatives which are found in all tissues of the potato plant including the tubers. The compounds are largely localized in the peel of tubers, but tissue beneath the peel rapidly accumulates the steroid glycoalkaloids to levels equal to or greater than those in the peel as a result of injury or environmental stress. The accumulation is restricted to the outer 1–2 mm of injured or stressed tuber. Potatoes containing over 0.02% steroid glycoalkaloids are considered toxic to man, and at this concentration they would impart a distinctly bitter flavor. The accumulation of steroid glycoalkaloids is suppressed and the accumulation of sesquiterpenoids is elicited in tubers infected by various pathogens and nonpathogens including the late blight pathogen,Phytophthora infestans. Arachidonic acid and eicosapentaenoic acids, two polyunsaturated fatty acids isolated fromP. infestans, are potent inhibitors of steroid glycoalkaloid accumulation. Both acids elicit the localized accumulation of sesquiterpenoids including rishitin, lubimin, phytuberin, phytuberol and solavetivone. Rishitin and lubimin generally comprise 85–90% of the total sesquiterpenoids which accumulate. The steroid glycoalkaloids and sesquiterpenoids appear to have a role in disease resistance to some fungal pathogens. Both groups of compounds are synthesized via the acetate-mevalonate pathway. Arachidonic and eicosapentaenoic acids appear to inhibit steroid glycoalkaloid accumulation at the level of the conversion of farnesyl pyrophosphate to squalene and they activate the biosynthesis of sesquiterpenoids. The reduction of steroid glycoalkaloids in potato foliage and tubers for health and flavor considerations should be considered relative to the ability of tubers and foliage to accumulate sesquiterpenoids in response to infection and its influence on disease and insect resistance.     

Origin and inheritance of solarmarine glycoalkaloids in commercial potato cultivars

Tuber tissues of 123 commercial cultivars were tested for their ability to synthesize solamarine glycoalkaloids. Eleven cultivars including ‘Kennebec’ and ‘White Rose’ synthesized major concentrations of solamarines, ranging between 42 and 85% of total glycoalkaloid, when tuber slices were exposed to light during wound-healing. Tuber tissues of the other 112 cultivars did not synthesize solamarines, or they synthesized only trace concentrations of these unusual glycoalkaloids. Nine of the 11 solamarine-synthesizing cultivars have a common ancestor, USDA 96-56. This parental clone synthesizes major solamarine concentrations and it also carries the R₁ gene for late blight resistance that it inherited fromSolatium demissum. Results of solamarine analyses of foliage from 47 USDA 96-56 selfed progeny suggest that this parental clone is the source of a major gene(s) for solamarines present in 9 of the commercial cultivars. However, there appeared to be an alternative source of a gene(s) for solamarines because ‘White Rose’, with onlyS. tuberosum ancestors, also synthesized major solamarine concentrations. There was no association between the R₁ gene for late blight resistance and the ability to synthesize solamarines in 31 USDA 96-56 selfed progeny that were analyzed for both characters.     

Hydrolysis of glycoalkaloids fromSolanum tuberosum L. haulm by enzymes present in plant material and by enzyme preparation

Summary This paper deals with the kinetics of enzymatic hydrolysis of glycoalkaloids from potato (Solanum tuberosum L.) haulm. The hydrolysis was carried out by the action of the enzymes present in fresh haulm, juice of fresh haulm and in haulm dried at various temperatures. The highest degree of enzymatic hydrolysis of 90% was obtained during fermentation of haulm dried at 40 °C after 30 h incubation time. The enzyme preparation was obtained from the juice of fresh potato haulm by using capillary dialysator HM 16 (AQM 1681, 1.6 m² Hemofan 8 υ). The best degree of enzymatic hydrolysis by enzyme preparation, 68%, was achieved after 20 h time of incubation. The enzyme preparation from juice of fresh haulm was characterized by K_m of 0.70 mM at pH 5.5 and 35 °C.     

The mass extraction of potato glycoalkaloids from blossoms

A new procedure has been developed to extract gram quantities of glycoalkaloids from freeze-dried potato blossoms. The per cent recovery is 65–70%, yielding a mixed glycoalkaloid product that is greater than 90% glycoalkaloids. This method is very simple and rapid with completion in only two days. This new methodology will be very useful in entomological and toxicological research where large amounts of these glycoalkaloids are utilized.     

Diploid and tetraploidSolanum chacoense genotypes that synthesize leptine glycoalkaloids and deter feeding by Colorado potato beetle

A selection (8380-1) fromSolatium chacoense Bitter (2n=2x=24) accession PI 458310 that synthesizes the leptine glycoalkaloids was compared in growth chambers with tetraploid (2n=4x=48) genotypes derived from tissue culture of 8380-1 leaf expiants for plant growth habit, leaf glycoalkaloid content, and effect on the development of Colorado potato beetle [Leptinotarsa decemlineata (Say)] larvae. The plants of the 4x regenerant genotypes were more vigorous with larger, more oval shaped leaflets than 8380-1 plants. The leaf concentrations of leptines and total glycoalkaloids were significantly lower (about 34%) in the 4x genotypes than in 8380-1. The proportion of leptines in the total glycoalkaloid content was nearly the same (about 80%) in both ploidy groups. In leaf-disk feeding tests, the development of Colorado potato beetle neonate larvae was not significantly different for the 2x and 4x genotypes. Both groups significantly slowed development compared with development on cv. Kennebec leaf disks. The 8380-1 selection and a group of 4x 8380-1 regenerant genotypes are maintained in the Vegetable Laboratory, Beltsville Agricultural Research Center, Beltsville, MD 20705 and are available for distribution.     

A new procedure for the mass extraction and collection of potato glycoalkaloids

A methodology for the collection of large volumes of potato glycoalkaloids from potato blossoms has been developed for use in preparative work. This new modification shortens and simplifies the laborious proceduresutilized heretofore and should prove a valuable aid for those requiring multiple gram quantities of pure glycoalkaloids for use in further research.     

A comprehensive method for the determination of total potato glycoalkaloids

A method has been developed for the quantitative analysis of total glycoalkaloids (TGA) in potato tubers. The method consists of TGA extraction by suitable solvent mixtures followed by hydrolysis of the glycosides and extraction of the aglycones. The aglycones are then quantitated by nonaqueous titration. The advantages of this method over those previously described are the inclusion of glycoalkaloids that are not measured by other methods, and the simplicity, safety, and rapid nature of the procedure. This method has been applied to the TGA analysis of potato tubers subjected to a variety of storage and treatment conditions.     

Development and production of monoclonal antibodies for the measurement of solanidine potato glycoalkaloids

Although it is generally acknowledged solanidine glycoalkaloids found in domestic potato cultivars are of sufficient toxicity to require testing prior to the release of new varieties, the widespread use of one of the most promising analysis techniques, immunoassays, is hampered by the variability of polyclonal antibody that has been developed for these analyses. We report the development of a uniform monoclonal antibody (mouse IgG1) that binds to solanidine and demissidine alkaloids for use in immunoassays. The monoclonal producing hybridoma developed is sufficiently resilient to produce the antibody in protein free media, from which very pure antibody could be isolated by simple ammonium sulfate precipitation. The purified antibody can be freeze-dried for storage and performs well in immunoassays with very low background absorbances. The monoclonal antibody was used in the optimized immunoassay at a concentration of 200 ng/mL with only 10 ng/mL concentration required for detectable signals (titer). From half absorbance levels (I₅₀ values) the antibody detected α-solanine the best (0.021 μM) while α-chaconine, demissidine and solanidine were detected at levels of 0.043, 0.092 and 0.103 μM, respectively.     

A method for the rapid estimation of glycoalkaloids in potato tubers

A rapid method for estimating glycoalkaloid levels in potato tubers has been developed. It is basically a screening technique whereby large numbers of samples can be assigned to categories of alkaloid level such as very low, low, medium and high. The elapsed time is typically four hours and the per sample time 12 to 15 minutes when large numbers are run. Weighed tuber samples are cut up and blended with a volume (ml) of extracting solution equal to the weight of the sample in g. After blending for four minutes, a portion of the extract is poured on to a fluted filter. An aliquot of the filtrate is treated with an antimony trichloride reagent and the color is read at 550 nm after 15 min.     

A technique for rapid detection of leptine glycoalkaloids in potato foliage

A rapid screening procedure for detecting the presence of leptines in potato foliage was developed. The glycoalkaloids in expressed sap are separated by high performance thin-layer chromatography and detected with iodine vapor. About 80 foliage samples can be analyzed per day as compared to about 10 using other available methods, such as gas-liquid chromatography.     

Total foliar glycoalkaloids and resistance of wild potato species toEmpoasca fabae (Harris)

Levels of total glycoalkaloids (TGA) in foliage of 10 wild, tuberbearingSolanum (Tourn.) L. species differentially resistant to infestation by the potato leafhopper,Empoasca fabae (Harris), were determined. Levels of TGA ranged from a high of 688 mg/100 g fresh wt. in a resistant species,S. polyadenium Greenm. to a low of 13 mg/100 g fresh wt. in a susceptible species,S. bulbocastanum Dun. Foliar concentration of TGA and nymphal infestation by the potato leafhopper were highly correlated (r = ?0.75, p = 0.01). The significant correlation of TGA levels and potato leafhopper resistance suggests that foliar TGA may be a significant factor in the defense of wild potato species against this pest.     

A rapid quantitative assay for solanidine glycoalkaloids in potatoes and industrial potato protein

Summary Aprapid quantitative assay for potato glycoalkaloids with solanidine (solanid-5en-3β-ol) as steriodal aglycone is described. The method of Sachse & Bachmann has been modified with respect to the extraction and working up procedures to increase the speed ans ease of analysis. A considerable simplification of analysis was achieved by replacing the original ether extraction and celite filtration by centrifugation. Fresh potato and industrial potato protein were analysed with this method. Industrial potato protein from several sources contained widely divergent glycoalkaloid contents (5–165 mg/100 g).     

Potato glycoalkaloids: Increases and variations of ratios in aged slices over prolonged storage

Four commercial cultivars of potatoes were maintained under normal storage conditions at 44 F for 34 weeks. Except for a final 10 week interval tubers were withdrawn at 6 week intervals. After slicing, a portion of the slices was immediately analyzed for total glycoalkaloid content. The remaining slices were aged for four days in the dark at room temperature, then similarly analyzed. The total glycoalkaloid content of the aged slices increased dramatically on aging. This increase on aging of slices reached a maximum early in storage then decreased gradually over the storage period. In determining the individual glycoalkaloids, α-solanine and α-chaconine both increased in these slices, but the greatest increase was in the former. Appearing solely in the aged slices of the Kennebec variety, α-and β-solamarine appeared early in the storage period and gradually decreased over the storage period. Analyses of the unaged slices indicated that the glycoalkaloid content and composition of the potato tubers was little affected by storage. Aging of potato sprouts did not change their glycoalkaloid content.     

Determination of total glycoalkaloids in potato tubers using a modified titration method

A new method for determining total glycoalkaloid content of potatoes (TGA) was developed by extensively modifying the comprehensive titration procedure of Fitzpatrick and Osman (1). This modified titration method eliminates the need to hydrolyze the glycoalkaloids and to purify the resulting aglycones by partitioning them into an organic solvent such as benzene or methylene chloride. Instead the glycoalkaloids are precipitated using ammonium hydroxide with the precipitate being dissolved in a tetrahydrofuran-water-acetonitrile (50:30:20) mixture. An aliquot is evaporated and quantitated using the nonaqueous titration procedure developed by Fitzpatrick and Osman (1). A comparison between this modified method and a high-performance liquid Chromatographic (HPLC) procedure was made using three commercial potato varieties and five experimental selections. Results from the two methods compared favorably.     

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.