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Biology Document BIO1996-09:
The Biology of Solanum tuberosum (L.)
(Potatoes)

A companion document to the Directive 94-08 (Dir94-08),
Assessment Criteria for Determining Environmental Safety of Plant with Novel Traits

Table of Contents

Part A - General Information

A1. Background

Since 1988, Agriculture and Agri-Food Canada (AAFC) has been regulating the field testing in Canada of agricultural and horticultural crop plants with novel traits (PNT's). "Plants with novel traits" are defined as a plant variety/genotype possessing characteristics that demonstrate neither familiarity nor substantial equivalence to those present in a distinct, stable population of a cultivated species in Canada and that have been intentionally selected, created or introduced into a population of that species through a specific genetic change. "Familiarity" is defined as the knowledge of the characteristics of a plant species and experience with the use of that plant species in Canada. "Substantial equivalence" is defined as the equivalence of a novel trait within a particular plant species, in terms of its specific use and safety to the environment and human health, to those in that same species, that are in use and generally considered as safe in Canada, based on valid scientific rationale.

The PNT's can either be derived from recombinant DNA technologies or from traditional plant breeding. Regulated field testing is necessary when the PNT's have traits of concern, i.e., the traits themselves, their presence in a particular plant species or their use are: (1) considered unfamiliar when compared with products already in the market; (2) not considered substantially equivalent to similar, familiar plant types already in use, and regarded as safe.

Before PNT's may be authorized for unconfined release, they must be assessed for environmental safety. Regulatory guidelines entitled: Assessment Criteria for Determining Environmental Safety of Plants with Novel Traits have been developed to define criteria and information requirements that must be considered in the environmental assessment of PNT's to ensure environmental safety, in the absence of confinement conditions.

A2. Scope

The present document represents a companion document to the Directive 94-08 (Dir94-08), entitled "Assessment Criteria for Determining Environmental Safety of Plants with Novel Traits". It is intended to provide background information on the biology of Solanum tuberosum (L.), its centres of origin, its related species and the potential for gene introgression from S. tuberosum into relatives, and details of the life forms with which it may interact.

Such species-specific information will serve as a guide for addressing some information requirements of Dir94-08. Specifically, it will be used to determine whether there are significantly different/altered interactions with other life forms, resulting from the PNT's novel gene products, which could potentially cause the PNT to become a weed of agriculture, become invasive of natural habitats, or be otherwise harmful to the environment.

The conclusions drawn in this document about the biology of S. tuberosum only relate to plants of this species with no novel traits. Novel traits of concern might confer new characteristics to the plant, that could impact on the environment pursuant to their unconfined release.

Part B - The Biology of Solanum tuberosum

B1. General Description, Use as a Crop Plant and Origin of Species

The potato (S. tuberosum) belongs to the Solanaceae family. This family includes, among 2000 other species, the tomato (Lycopersicum esculentum), sweet pepper (Capsicum annuum), eggplant (S. Melongena var. esculentum), tobacco (Nicotiana tabacum), and petunia (Petunia hybrida). The genus Solanum is a polymorphous and largely tropical and subtropical genus containing more than 1000 species (Fernald, 1970).

The potato is one of the world's most important crops, following wheat, maize, and rice. It has weak stems that grow to a maximum of three feet, long pinnate leaves, ovate leaflets with smaller ones disposed along the midrib. The flowers are white, purple, pinkish, or bluish, in clusters, usually with a five parted corolla and exserted stamens with very short filaments. Some varieties are male sterile, suffer from abscission of flowers, and rarely produce fruits. The fruits are yellowish or green, globose, less than one inch in diameter, some lack seeds, but others may contain several hundred. The fruits are inedible to humans, due to the presence of toxins (Hortus Third, 1976). Solanum species have an initial chromosome number of 12, but polyploidy is prevalent in both wild and cultivated potatoes.

All potatoes cultivated in Canada belong to the species S. tuberosum, a species widely cultivated as an annual in temperate regions for its edible underground tubers. The tubers are utilized for food, feed and as seed propagules. In North America, the crop is grown primarily for human consumption and for seed. In some areas, starch is manufactured from surplus production and cullage. Starch manufactured from potatoes has a wide range of end uses. The most extensive use is for sizing and coating in the paper industry. In the food industry, starch may be used in the preparation of instant puddings, in the manufacture of ice cream, as an additive to breads and biscuits, as a thickener in soups and a variety of other preparations in home cooking. Potatoes utilized for food may be fresh or processed; the cultivars grown for processing are also acceptable for fresh consumption or table stock, while some table stock cultivars are not suitable for processing and are limited to the fresh market. Fresh potatoes are usually prepackaged in consumer packs or may be sold at retail in open displays. The single most important processed product is frozen french fried potatoes and there is a significant production of potato chips. The processed potato products are usually preserved by freezing, canning and dehydrating and are prepared in a variety of consumer products. Tubers used as livestock feed are usually cullage from fresh pack operations, surplus production or waste from processing plants.

Potatoes are grown in all provinces and territories of Canada. The surface area devoted to commercial potato production in 1995 was 144,700 hectares. The average yield for the same period was 26.27 tonnes per hectare, giving an average production of 3.78 million tonnes. On a regional basis, Canadian commercial production was distributed in 1995 as follows: New Foundland, Nova Scotia, New Brunswick and Prince Edward Island, 50%; Ontario and Quebec, 24%; and Manitoba, Saskatchewan, Alberta and British Columbia, 26%. Production is expanding rapidly in Prince Edward Island, and to some extent in Manitoba and Alberta. Production has remained relatively constant in all other provinces.

B2. Brief Outlook of Agronomic Practices for the Potato (from Hortus Third, 1976)

Cold summer temperatures are ideal for potato production. It is also essential to have ample soil moisture for optimum yields. Tuber formation in potatoes is favoured by short days. The potato does not breed true, and seeds may differ genetically in the same fruit and from the parent plant. Therefore, the seeds are of value only to the plant breeder who wishes to develop new genotypes. Ordinary propagation is through the planting of tubers or pieces of tubers presenting at least one eye. These propagules are known in the industry as "seed", not to be confused with true or botanical seed. Each eye of a potato tuber is made up of a rudimentary scale leaf and a multiple bud cluster. For each row of cultivated potatoes, the soil is ridged up to prevent exposure of the developing tubers to light. Tubers exposed to the light turn green and produce an antinutritional alkaloid, which renders them unfit for human or livestock consumption. For the same reason, potatoes should be stored in a dark place after harvest.

High application rates of nitrogen, phosphorus and potash are required for best yields in most locations, and magnesium is frequently needed in acid soils. Potatoes may be planted before the usual date of the last killing frost. Although the foliage is only moderately tolerant of frosts, new shoots will emerge if the seed pieces are still sound at the time of any frost damage.

There are many serious diseases that may be carried in seed potatoes, such as scab, a disease which causes corky lesions on the skin of the potato. Potatoes can also be attacked by such diseases as late blight and early blight, bacterial ring rot and virus diseases. The only protection against such diseases is to use certified disease free seed potatoes. A number of insects can attack the developing plant. Perhaps the most serious of these is the Colorado potato beetle, which can cause extensive foliar damage. Other insects attacking foliage include potato flea beetles, leaf hoppers, and aphids.

B3. The Reproductive Biology of S. tuberosum

The cultivated potato is an annual and may be reproduced by seed although the commercial crop is propagated from tuber "seed" pieces (Rowe, 1993). In the context of true seed production, the degree to which flowering occurs, the duration of flowering and the response of flowering behaviour to environmental conditions is greatly influenced by cultivar (Burton, 1989). The environmental conditions that influence flower initiation and development include light intensity, quality and duration (day length), temperature, water supply and available soil nutrients. Flower development does not ensure fruit set. Pollen sterility is frequently encountered, in which case pollinating insects may not be attracted due to poor nectar production, and ovule sterility is also occasionally experienced.

True seed production is practised in breeding programs, and under greenhouse conditions. It requires skilled manipulation of variables to be successful. True seed production in the natural environment varies with cultivars and weather conditions. Many varieties do not produce any seed, while some varieties are either self-pollinated or cross-pollinated and do produce seeds.

B4. The Centres of Origin of the Species

The potato originates from regions of high elevation of South America. The area of first domestication is reasoned to be the area where wild diploids are still found and where the greatest diversity of cultivated forms can still be found, and is identified as the high plateau of Bolivia and Peru, in the general region of Lake Titicaca (Hoopes and Plaisted, 1987).

Many authors have traced the origin and distribution of the potato (Burton, 1989; Dodds, 1965; Hawkes, 1967; Howard, 1970; Salaman, 1949; Simmonds, 1976). These authors essentially agree that the significant species considered to be the progenitors of the cultivated potato are from South America. Simmonds (1976) indicates these may be found to 45° S latitude in South America and to 40° N in North America.

Yield and quality enhancement have marked the changes that emerged with the introduction of plant breeding programs in Europe and North America in the 19th century. The need for pest resistance was introduced with the late blight (Phytophthora infestans) infestation of the 1840's, and, in the 20th century, a need for resistance to viruses and nematodes. This resistance was attempted through the use of S. demissum for late blight, S. stoloniferum, S. chacoense and S. acaule for viruses and S. multidissectum, S. spegazzinii, S. kurtzianum, S. oplocense and S. vernei for nematodes. These wild species have been used extensively in breeding programs (Burton, 1989; De Jong and Tarn, 1984; Howard, 1970; Simmonds, 1976).

B5. Cultivated S. tuberosum as a Volunteer Weed

Some varieties of the cultivated potato produce true seed. In Southern England, this seed can survive for up to seven years (Lawson, 1983). In Canada, most production areas experience deep frost penetration in the soil profile and tubers that set on plants produced from true seed are regularly purged from the soil environment. In addition, plantlets that grow from true seed are easily controlled with normal weed control practices and do not usually set tubers. Thus, in land areas where potatoes are grown commercially, the measures required to control volunteers that result from true seed being dispersed do not differ from the cultural and pest management practices that are normally followed for the crop and succeeding crops in the rotation. Outside of cultivated areas, seedlings grown from true seed do not compete successfully and are not reported as a weed pest in these areas.

Vegetative volunteers may result from tubers that are left at harvest time. Plants established from such tubers have failed to survive outside of cultivated areas. In cultivated areas, they may become a short-term weed problem, but a combination of weed control efforts and unfavourable environmental conditions limits weediness to one or a few years only (Makepeace et al., 1978). The possibility for vegetative escape of tubers, however, is present in the handling and transportation of potatoes. Even though volunteers occur periodically near animal feed lots, at waste disposal sites and in areas surrounding commercial production sites, there is no evidence that potato plants will proliferate and become established as a weed. Evenhuis and Zadoks (1991), have concluded that this is the case because S. tuberosum is at a competitive disadvantage and does not survive in the wild.

B6. Summary of Ecology of S. tuberosum

S. tuberosum is not a primary colonizer in unmanaged ecosystems. Seedlings of this species do not compete successfully against plants of similar type for space. In climax ecologies they are displaced by grasses on prairies or tree species and perennial shrubs in forests and, in Canada, do not survive outside of cultivation for significant periods of time.

In crop production systems, volunteer tubers and plants are removed with the production practices that are normally used for potatoes and the crops that succeed potatoes in the rotation.

S. tuberosum is not listed as a noxious weed in the Weed Seed Order (1986). It is not reported as a pest or weed in managed ecosystems in Canada, nor is it recorded as being invasive of natural ecosystems. In summary, there is no evidence that in Canada S. tuberosum has weed or pest characteristics.

Part C - The Close Relatives of S. tuberosum

C1. Inter-Species/Genus Hybridization

Important in considering the potential environmental impact following the unconfined release of genetically modified S. tuberosum, is an understanding of the possible development of hybrids through interspecific and intergeneric crosses with the crop and related species. The development of hybrids could result in the introgression of the novel traits into these related species and resulting in:

• the related species becoming more weedy
• the introduction of a novel trait with potential for ecosystem disruption into the related species.

This section will be subject to updating, as more data becomes available. Based on background information provided in the present document, applicants will need to consider the environmental impacts of potential gene flow.

For a trait to become incorporated into a species genome, recurrent backcrossing of plants of that species by the hybrid intermediaries, and survival and fertility of the resulting offspring, is necessary.

C2. Potential for Introgression of Genetic Information from S. tuberosum into Relatives

Less than a tenth of the Solanum species are tuber-forming and, so far as is known, these occur only in the Americas, between mid-USA to the north and southern Chile and Argentina to the south (Burton, 1989). S. fendleri and S. jamesii, found in the southern part of the United States, can produce hybrids with S. tuberosum plants under controlled laboratory conditions (Adiwilaga and Brown, 1991). These species occupy dry forest at high altitudes, and therefore are quite unlikely to cross with cultivated potato plants under natural conditions due to geographical separation.

As a general rule, S. tuberosum can only hybridize naturally with Solanum species that form tubers (Dale et al., 1992; Evenhuis and Zadoks, 1991), none of which are present in Canada (Love and Pavek, 1994). Gene introgression to related native species through hybridization is therefore not possible (Love and Pavek, 1994 and other authors cited previously).

C3. Occurrence of S. tuberosum in Canada

The occurrence of S. tuberosum is limited to commercial production for harvest of tubers. Occasionally, plants and seedlings grow as volunteers from escape tubers and true seeds, but these do not become established in Canada as persistent weeds. S. tuberosum is not reported as a weed in Canada.

Part D - Potential Interactions of Solanum tuberosum with Other Life Forms

Table 1 is intended to guide applicants in their considerations of potential impacts the release of the PNT in question may have on non-target organisms, but should not be considered as exhaustive. Where the impact of the PNT on another life form (target or non-target organism) is significant, secondary effects may also need to be considered.

Table 1. Examples of potential interactions of Solanum tuberosum with other life forms during its life cycle.

Part E - Acknowledgments

This document was developed with the support of the following organizations:

• Alberta Potato Research Association
• Atlantic Canada Opportunities Agency
• Canadian Agri-Food Development Initiative
• Canadian Institute of Biotechnology
• International Centre for Agricultural Science and Technology
• McCain Produce Inc.
• Monsanto Inc.
• NatureMark Potatoes
• New Brunswick Potato Agency
• Ontario Potato Growers Marketing Board
• PEI Potato Board

Part F - Bibliography

Adiwilaga, K. D. and C. R. Brown (1991) Use of 2n pollen-producing triploid hybrids to introduce tetraploid Mexican wild species germplasm to cultivated tetraploid potato gene pool. Theor. Appl. Genet. 81: 645-652.

Burton, W. G. (1989) The potato - 3rd ed. John Wiley & Sons Inc. New York. 742 pp.

Dale, P. J., H. C. McPartlan, R. Parkinson, G. R. MacKay and J. A. Scheffler (1992) Gene dispersal from transgenic crops by pollen. In: Proceedings of the second international symposium on the biosafety results of field tests of genetically modified plants and microorganisms. Goslar Germany, 1992. pp. 73-77.

De Jong, H. and T. R. Tarn (1984) Using germplasm in potato breeding in Canada. In: Canada Agriculture No. 3 & 4, Communications Branch, Agriculture Canada, Ottawa Ontario.

Dodds, K. S. (1965) The history and relationships of cultivated potatoes. In: J. B. Hutchinson, ed., Essays in crop plant evolution, London, pp.123-41.

Evenhuis, A. and J. C. Zadoks (1991) Possible hazards to wild plants of growing transgenic plants. A contribution to risk analysis. Euphytica 55: 81-84.

Fernald, M. L. (1970) Gray's manual of botany. A handbook of the flowering plants and ferns of the central and northeastern United States and adjacent Canada. D. Van Nostrand Co. p.1252.

Hawkes, J. G. (1967) The history of the potato. F. Roy. hort. Soc.: 92; 207-24; 249-62; 288-302; 364-65.

Hoopes, R. W. and R. L. Plaisted (1987) Potato. In: Principles of cultivar development. Volume 2. Crop species. W. R. Fehr, E. L. Fehr, H. J. Jessen, eds. Macmillan Publishing Company, N.Y. pp. 385-436.

Hortus Third (1976) A concise dictionary of plants cultivated in the United States and Canada. Liberty Hyde Bailey Hortorium, ed. Macmillan Publishing Company, Cornell University pp.903-04; 1054.

Howard, H. W. (1970) Genetics of the potato: Solanum tuberosum. Logos Publishing, London. 126 pp.

Lawson, H. M. (1983) True potato seeds as arable weeds. Potato Research 26: 237-46.

Love, S. L. and J. J. Pavek (1994) Ecological risk of growing transgenic potatoes in the United States and Canada: potential for vegetative escape or gene introgression into indigenous species. Am. Potato J. 71(10): 647-58.

Makepeace, R. J., D. C. Cooper and J. Holroyd (1978) Weed control. In: The Potato Crop, P. M. Harris, ed. Halsted Press, New York. pp. 402-05.

Rowe, R. C. (1993) Potato Health Management. The American Phytopathological Society, St Paul, Minnesota, USA, pp. 4.

Salaman, R. N. (1949) The history and social influence of the potato. University Press. Cambridge. 685 pp.

Simmonds, N. W. (1976) Evolution of Crop Plants. Longman, London and New York. 339 pp. Weed Seed Order (1986) Canada Seeds Act.

This bulletin is published by the Plant Health and Production Division, Canadian Food Inspection Agency. For further information, please contact the Plant Biosafety Office at:

Plant Biosafety Office
Plant Products Directorate
Canadian Food Inspection Agency
59 Camelot Drive
Ottawa, Ontario K1A 0Y9
Telephone: (613) 225-2342
Facsimile: (613) 228-6629