Glycoalkaloid contents in tubers fromSolanum tuberosum populations selected for potato leafhopper resistance

Solanum tuberosum L. Gp. Tuberosum populations that had been improved for resistance to potato leafhopper,Empoasca fabae (Harris), by recurrent selection, were analyzed for tuber contents of the glycoalkaloids α-solanine and α-chaconine. The mean content of both glycoalkaloids was significantly higher in the more resistant populations compared with the unselected population. In a population generated from seven cycles of selection for resistance, the mean content of solanine + chaconine was 9.5 mg/100 g fresh weight compared with 4.0 mg/100 g in the original, unselected population; a 137% increase. Kennebec, in the same experiment, averaged 10.9 mg/100 g; Katahdin averaged 4.6 mg/100 g.     

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.     

The effect of light intensity on Colorado potato beetle resistance and foliar glycoalkaloid concentration of fourSolanum chacoense clones

Controlled environment experiments were used to determine the effect of light intensity on levels of glycoalkaloids and resistance to the Colorado potato beetle (CPB),Leptinotarsa decemlineata Say, inSolanum chacoense Bitter clones that synthesized acetylated glycoalkaloids, the leptines. Plants were grown under two light intensities, 50 or 250 ?mol m^-2S^-1, and bioassayed for CPB resistance by placing neonate larvae on excised foliage. Larval development stage and mortality were recorded after four days. The leptine-synthesizing clones responded to the increase in light intensity with a 2–4 fold increase in level of foliar leptines. Larval development rate on foliage from plants grown under high light intensity was reduced and larval mortality increased. Results showed a significant (p>0.05) effect of light on glycoalkaloid synthesis and CPB resistance.     

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.     

Performance of Colorado potato beetle larvae,Leptinotarsa decemlineata (Say), reared on synthetic diets supplemented withSolanum glycoalkaloids

Glycoalkaloids are a class of secondary compounds (nitrogenous, steroidal glycosides), ubiquitously distributed throughout the Solanaceae. Numerous studies (in planta) have shown that certain glycoalkaloids, e.g., α-tomatine, solanocardenine, and leptine, have a negative impact on performance of the Colorado potato beetle,Leptinotarsa decemlineata (Say). However, the presence of other secondary compounds, as well as the nutritional status of the plants used, are additional variables in such experiments. By rearing Colorado potato beetle, from egg to prepupal stage, on a synthetic diet supplemented with the glycoalkaloids α-tomatine, α-chaconine, α-solanine, leptine I and the steroidal aglycone solanidine, we have been able to further establish the effects (ex planta) of these compounds on the Colorado potato beetle. Leptine I displayed a dose-dependent negative activity against the Colorado potato beetle (as measured by larval weight gain and tune to molt), when assayed at 0.31, 0.62 and 1.23 mM concentrations; however, by the fourth stadium no effect was found. When Colorado potato beetle were fed a higher concentration of leptine I (2.4 mM), there was a sustained effect in all stadia. At 2.4 mM, leptine I displayed a greater negative impact on Colorado potato beetle growth and development than did α-tomatine. α-Chaconine at 2.4 mM did not impair Colorado potato beetle performance relative to Colorado potato beetle reared on control diets. α-Chaconine plus α-solanine, at concentrations commonly found inSolanum tuberosum L. foliage (0.6 and 0.3 mM respectively), did not impair Colorado potato beetle performance. The steroidal aglycone solanidine (2.4 mM) had a significant negative impact on Colorado potato beetle performance. Results are discussed in the context of host-plant resistance and insect-plant interactions.     

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.     

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.     

Segregation of leptine glycoalkaloids and resistance to Colorado potato beetle (Leptinotarsa decemlineata (Say)) in F2Solanum tuberosum (4x) ×S. chacoense (4x) potato progenies

Solanum chacoense Bitter is resistant to the Colorado potato beetle (CPB),Leptinotarsa decemlineata (Say). Resistance has been associated with the presence of a rare class of glycoalkaloids, the leptines. In this study, seven tetraploid, F2S. tuberosum xS. chacoense families were evaluated for foliar production of leptines I and II, leptinines I and II, and α-solanine and α-chaconine; and screened for resistance to CPB in the laboratory and field. Resistance was correlated with the concentrations of glycoalkaloids on a family and an individual basis. Leptine concentrations ranged from undetectable to a high of 18.0 mg/g dry weight. All of the progeny produced solanine and chaconine. Family 9623 had the highest mean leptine concentration and the lowest mean leaf disk feeding and CPB defoliation levels. Family 9616 had the lowest mean glycoalkaloid concentration and ranked as one of the most susceptible families. Regression analyses of solanine + chaconine, leptine I and II, and leptinine I and II foliar concentrations versus leaf disk consumption and field defoliation revealed that only increased foliar levels of leptines resulted in decreased CPB feeding. The regression models for leptines versus leaf disk consumption and field defoliation were highly significant, accounting for 17% and 26% of the variation in consumption and defoliation, respectively. To the best of our knowledge, this is the first work reporting the impact of leptine and leptinine concentrations on CPB feeding in tetraploid,S. tuberosum xS. chacoense potato hybrids. Results are discussed within the context of breeding for resistance to CPB.     

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.     

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.     

Resistance of potato clones to the green peach aphid and potato leafroll virus

During 1980 and 1981 potato cultivars and breeding selections, including cultivated species and their hybrid derivatives, were evaluated for resistance to the green peach aphid (GPA),Myzus persicae (Sulzer), and to potato leafroll virus (PLRV). Criteria used were the number of aphids which colonized the clones in free choice field experiments and the number of plants derived from these experiments which showed symptoms of PLRV infection. Generally, greater resistance to GPA was found inSolarium tuberosum gp.andigena selections and hybrids than in gp.tuberosum cultivars. There were approximately fourfold differences in season-mean GPA levels among the clones tested each year. Forty-two families, representing a cross-section of the USDA breeding populations at the University of Idaho Research and Extension Center, Aberdeen, showed a similar range in colonization levels. Resistance to GPA colonization appeared to be more prevalent in gp.andigena, gp.phureja, and gp.stenotonum derivatives. There was a weak positive correlation (r² = .34, P = .01) between foliar total glycoalkaloids and season-mean GPA colonization levels for six clones representing the range of observed resistance to GPA. Resistance to GPA colonization was apparently not directly related to resistance to PLRV infection. Katahdin, for example, was relatively susceptible to GPA colonization but very resistant to PLRV infection whereas selection A69657-4 (gp.andigena) was among the most resistant to GPA colonization but among the more susceptible to PLRV infection. Breeding for resistance to GPA colonization therefore may not be as promising for PLRV control as developing PLRV resistant cultivars.     

The nutritional value of pressed potato vine silage

Potato (Solanum tuberoswn L.) vines were studied to determine if they could be successfully ensiled and fed to ruminant animals. Russet Burbank potato vine and alfalfa (Medicago sativa L.) silages were fed to goats (Capra hircus) to measure in vivo digestibility and to determine if potato glycoalkaloids were aversive or toxic. No differences in the feeding patterns between control and experimental animals were observed. Alfalfa silage was more digestible than the Russet Burbank potato vine silage due to a higher content of digestible cell wall materials. Digestibility differences between potato clones and harvest dates were found when in vivo digestibility tests were performed. W729R was the most digestible clone studied, especially for the early harvest dates. Most of the clones had vines that were more digestible, in vitro, than alfalfa. Vine glycoalkaloid contents of the experimental clones were similar to the values reported in the literature. There was no apparent correlation between vine glycoalkaloid content and percent digestible dry matter. A positive correlation of 0.38 between digestible dry matter and dry vine yield was found. Potato vine silage, produced after pressing the vines to remove water, was an acceptable feed for ruminant animals. Additional in vivo testing is necessary to determine if toxic effects due to glycoalkaloids or pesticides from long term feeding will be a problem.     

Evaluation of Vitamins and Glycoalkaloids in Potato Genotypes Grown Under Organic and Conventional Farming Systems

Potato tubers provide people not only with carbohydrates but also with other essential compounds for human health. Several investigations have compared the quality of crops grown under organic and conventional farming systems. The aim of the present study was to evaluate the concentrations of vitamins C, B₁ and B₂ as well as glycoalkaloids (α-solanine and α-chaconine) in potato tubers of different genotypes and to estimate the farming system (conventional and organic) impact on the content of these compounds. Twenty potato genotypes were grown under organic and conventional farming systems in Priekuli (Latvia) during 2010 and 2011. The concentrations of vitamins C, B₁ and B₂ as well as glycoalkaloids (α-solanine and α-chaconine) were significantly influenced by the potato genotype. The vitamin B₁ concentration of potato genotypes grown in the organic field exceeded that of potato genotypes grown in the conventional field. A significant negative correlation was found between the vitamin C concentration and tuber yield only in the conventional field. No significant correlations were found between the other potato characteristics, such as starch content, tuber taste after boiling and glycoalkaloids, vitamins C, B₁ and B₂. The high broad-sense heritability for all tested traits (vitamin C 93%, vitamin B₁ 92%, α-solanine 88%, α-chaconine 84% and vitamin B₂ 70%) demonstrated that the high genetic diversity in the potato genotype population accounted for the phenotypic expression. The present study suggested that the breeding of new potato varieties with improved nutritional quality can be launched, and that the varieties that will be developed can be produced in an environmentally friendly way.     

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.     

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.     

Production of phytoalexins, glycoalkaloids and phenolics in leaves and tubers of potato cultivars with different degrees of field resistance after infection withPhytophthora infestans

Summary The kinetics of accumulation of phytoalexins, glycoalkaloids and phenolics was studied in two potato cultivars differing in their degrees of field resistance when infected withPhytophthora infestans. Tuber slices and leaves of cvs Pampeana INTA (high degree of field resistance, free of R genes) and Bintje (susceptible) were infected with race C (complex race 1, 3, 5, 7, 11) ofPhytophthora infestans. Phytoalexins and phenolics accumulated in tuber and leaf tissues which had been inoculated. The levels of these compounds in the susceptible cv. Bintje were relatively low and similar to those found before inoculation. Leaves of cv. Pampeana INTA had a very high glycoalkaloid content, suggesting that glycoalkaloids may play a role in protection of leaves against the fungus. However, we could find no correlation between resistance and glycoalkaloid content of tubers. Our results suggest a major role of phytoalexins, phenolics and glycoalkaloids in the complex mechanisms of field resistance.     

Effect of potato seed tuber glycoalkaloid content on subsequent infection byRhizoctonia solani

Since glycoalkaloids have been shown to have fungitoxic properties, it is important to know what impact this might have on potato plant breeding programs which select for low levels of total glycoalkaloids (TGA) in the tuber. Potato clones with TGA levels ranging between 1.6 and 32.8 mg/100 g fresh tissue were planted in two trials to evaluate the relationship between seed tuber TGA and incidence ofRhizoctonia solani infection in the developing plant. An inoculation procedure was followed in the greenhouse and field to establish uniform infection of potato seedlings. Plants were examined for lesion development on stems and stolons and assigned disease ratings. In the field, yield of malformed tubers was recorded and included in the overall disease ratings. The results reported herein indicate that TGA levels in the seed tuber are unrelated to the severity ofR. solani infection in the seedling.     

The Inter-genebank potato database and the dimensions of available wild potato germplasm

The Association of Potato Inter-genebank Collaborators (APIC) constructed a database of all wild potato holdings of the most important potato genebanks in Europe, the United States, Peru, and Argentina. The Inter-genebank Potato Database (IPD) now contains data of 11,819 wild potato accessions conserved in seven potato genebanks. The collector’s number is the key identifier used to merge all databases into the IPD. A total of 7,112 different wild potato accessions were identified, which comprise 5,306 accessions with known collector’s numbers. The IPD passport database showed that almost 30% of accessions held in APIC genebanks are from Argentina, a country that comprises less species diversity than Peru and Bolivia. These latter countries are represented by 24% and 20% of accessions, respectively. APIC genebanks maintain 188Solarium taxa out of more than 230 recognized by the latest comprehensive treatment of potatoes(Solarium sect.Petota) by Hawkes (1990). About 60% of the accessions comprise only 20 taxa represented by 785 to 92 accessions each. Conversely, 2% of the accessions comprise 72 taxa and are represented by five or fewer accessions each. About 70 taxa are not available in any genebank. The IPD evaluation database comprises 5,603 records with data from more than 33,000 evaluations of wild potato accessions. Fifty-five traits are summarized, including the reactions of the accessions to 12 pathotypes or races or strains of 12 fungi, four bacteria, 12 viruses, one viroid, 13 nematodes, and seven insects; response to heat and cold stress; and content of dry matter, starch, vitamin C, amylase, reducing sugars, and glycoalkaloids. About 30% of the wild potato populations screened showed various levels of resistance to most of the diseases and pests evaluated. The IPD database is available on the Internet at www.potgenebank.org.     

Mechanisms of resistance to potato leafhopper,Empoasca fabae (Harris), in potato

Potato genotypes were evaluated for resistance to natural infestations of the potato leafhopper,Empoasca fabae (Harris), in the field. Characterization of Type A and B glandular trichomes, phenolic properties of Type A trichomes, glycoalkaloid content and composition,E. fabae adult and nymph infestation, leaf damage (hopperburn), yield, and yield reduction were determined on genotypes PI 473331 and PI 473334 (accessions ofSolatium berthaultii (Hawkes)), NY123 and Q174-2 (advanced hybrids), and Elba and Allegany (commercial cultivars). Regarding the Type A trichome, PI 473334 was most pubescent, followed by PI 473331, both had high levels of enzymatic browning; on PI 473334 no glycoalkaloids were detected, while on PI 473331 solamargine and solasonine were present. Those genotypes were the least infested by adults; moreover, nymphs were never found on their leaves. PI 473331 and Q174-2 possess Type B trichomes, the latter had levels of Type A trichome comparable to the first and to NY123, while displaying high levels of phenolic oxidation of Type A and very low levels of glycoalkaloids. Although Q174-2 had intermediate infestation ofE. fabae, it suffered a yield reduction comparable to the control cultivar Allegany. The density of Type A trichomes of NY123 was relatively low, even though the browning assay results were significantly elevated. Foliage of this genotype was found to contain the four types of glycoalkaloids studied at high levels.Empoasca fabae infestation on NY123 was intermediate, and it yielded well on infested plots, but suffered an intermediate yield reduction. Elba presented densities of Type A similar to NY123. It suffered the lowest yield reduction despite its high levels of leafhopper infestation and hopperburn. Its tolerance might be associated with its phenology, since it is a late-maturing cultivar. High scores of the modified enzymatic browning assay were correlated with high infestation and high leaf damage. Results indicated a significant correlation between leafhopper infestation and hopperburn.     

Soft-rot Resistance of Coloured Potato Cultivars (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.): The Role of Anthocyanins

Coloured potatoes (Solanum tuberosum L.) rich in anthocyanins are gaining increasing interest on the markets, mainly due to beneficial health effects. Potato varieties containing colour pigments are therefore utilized more and more in actual breeding programmes. In this study, 10 purple-fleshed potato cultivars were compared in their resistance to soft rot caused by Pectobacterium carotovorum (Pc) with 10 white/yellow-fleshed potato cultivars. The results revealed that coloured potato cultivars exhibited on average better resistance to soft rot than white/yellow-fleshed potato cultivars. On tuber halves of purple-fleshed cultivars, the extent of rotting caused by Pc was on average 28.6% lower than on white/yellow-fleshed cultivars. The greater resistance of coloured potatoes coincided with the presence of anthocyanins, higher concentrations of soluble phenols and elevated polyphenol oxidase activity in tuber tissue. These three components were significantly correlated with the extent of rotting caused by Pc. However, coloured and white/yellow-fleshed cultivars were not very different in phenylalanine ammonia-lyase and peroxidase activity. There were also no significant differences in concentrations of dry matter, starch, crude protein and glycoalkaloids. Key findings reveal that total soluble phenols and anthocyanins contributed crucially to resistance expression in tuber tissue of coloured potato cultivars.