Solanum tuberosum
(potato)

Solanum tuberosum is native to Central and South America, but is now widely naturalized beyond its native range in extra-tropical regions and is considered a weed in many places including Australia, Indonesia, Micronesia, India, and Turkey (Holm et al., 1979; Randall, 2012). It has been declared a noxious weed in the United States, Turkey and South Africa (Randall, 2012) and listed in the American Lands Alliance’s “Worst Invasive Species in the conterminous United States” list (Randall, 2012). It is considered an agricultural weed on plantations and cultivated fields in parts of the Pacific Islands where it has been introduced (Randall, 2012). Because of the species’ global importance as a staple food crop, caution and vigilance is essential when cultivating the species in order to minimize escape into the wild.

The species of Solanum are considered native to Central and South America, mainly to the highland plains ('puna') and Andes mountains between 40°N and 45°S. S. tuberosum is considered native to the Peruvian-Bolivian Andes region, but has been introduced to most parts of the world. It is cultivated throughout the West Indies (Acevedo-Rodriguez and Strong, 2012) and the upland regions of Mesoamerica (Gentry and D’Arcy, 1986), as well as throughout Europe, in much of Asia, and in many other regions. The Distribution Table does not list all the countries where S. tuberosum is grown as a crop.

Based on the current literature, the species poses a risk to native flora. It is a declared noxious weed in the United States and South Africa (Randall, 2012; USDA-NRCS, 2014) and listed in the American Lands Alliance’s “Worst Invasive Species in the conterminous United States” list (Randall, 2012). It is considered an agricultural weed on plantations and cultivated fields in parts of the Pacific Islands where it has been introduced (Randall, 2012). Because of the species’ global importance as a staple food crop both in the international commercial industry and on the local scale, caution and vigilance is essential when cultivating the species in order to minimize cultivation escape into the wild.

S. tuberosum is one of the most important food crops of the world, and grown in cool-temperate regions and at higher altitudes in the tropics (Wagner et al., 2014). It is native to the mountainous areas of Bolivia, Chile and Peru. It is an important food crop in the mountainous countryside of China (An-ming, 1986). In Antioquia, Colombia the species has been reported growing in Lower Montane Rain Forest (bh-MB) and Lower Montane Wet Forest (Vascular Plants of Antioquia, 2014), while in Bolivia it is recorded growing in dry valleys, the Yungas forest, and humid puna grassland of the central Andes region (Bolivia Checklist, 2014).

Genetics

There are numerous cultivars of S. tuberosum. Sporophytic count has been reported as 2n=24, 36, 48, 72, 96 (Wagner et al., 2014; IPCN Chromosome Reports, 2014).

Botanical Information

Tetraploid S. tuberosum can be classified into two cultivar groups, with the following characteristics:

- cultivar group Andigena (subsp. andigena), mainly occurring in South America from Venezuela to northern Argentina and is supposed to have originated by chromosome doubling in an unknown wild diploid species from the Andean region between Bolivia and Venezuela. Its members are tall, often straggling; leaves intensively dissected with numerous leaflets; adapted to short days; they usually produce rather irregularly shaped, deep-eyed and often pigmented tubers that are usually not acceptable to the more sophisticated markets of Europe and North America. They are also grown to a small extent in Mexico and Guatemala.

- cultivar group Tuberosum (subsp. tuberosum), mainly occurring in Europe and North America, supposed to have originated from selections made during the last 300 years from cv. group Andigena. Its members are smaller, less straggling, with less dissected leaves and are adapted to long days. This group has become a world crop and is now cosmopolitan in distribution. It was first introduced into Europe where selection began and from where cultivars spread to North America. With growing interest in the crop, supplementary introductions from South America were made to both these regions. Continuing selection has led to the establishment of numerous cultivars, a process still going on wherever the crop is grown. Cultivars vary in characteristics of their tubers, sprouts, foliage, flowers, growth cycle and disease resistance; much of the variability is also influenced by the environment. Propagation by true seed, however, produces variability due to genetic recombination.

Growth and Development

The general growth and development patterns of potato plants are characteristic within cultivars, but also vary with the environment and fertilizer treatments.

After harvest, tubers usually enter a period of dormancy, the duration of which depends on cultivar, maturity of the tuber, soil and climatic conditions during growth, and storage conditions. It often lasts for 2-6 months, but in some cases bud growth has already started before harvest. High temperatures during growth and storage tend to shorten dormancy and low temperatures prolong the dormancy period. Dormancy can be broken by treating tubers with chemicals such as chlorohydrin, thiourea or gibberellic acid. However, naturally sprouted tubers without the use of chemicals are preferred as they give more uniform germination and better growth. Once the period of natural dormancy has ended, the seed tuber passes through various subsequent physiological stages: apical dominance of sprouts, multiple sprouting and senility. An apical sprout is dominant over the other buds, so these remain dormant. Only when this apical or top sprout is removed (de-sprouting) will the other buds of the tuber develop sprouts during this phase. The degree of apical dominance depends on the cultivar. The optimum stage for planting is multiple sprouting, not only because of the number of sprouts, but also because of the vigour of individual sprouts. The number of sprouts (germinating eyes) per tuber depends on the extent of apical dominance, which is affected by variety, tuber age and physiological age as affected by chitting. It also depends on nutrition, tuber size and tuber health. After prolonged storage seed tubers may reach the stage of senility and have then become unfit for planting.

After planting, sprouts develop into stems. A main stem grows directly from the seed tuber. The lower lateral branches from the main stem are called secondary stems. Apart from secondary stems, a stem may develop branches at higher nodes several times during its growth. Main and secondary stems grow and behave like independent plants, and develop roots, stolons and tubers. Plant population is, therefore, best expressed as number of stems, rather than number of plants.

In plants growing from tubers, adventitious roots arise from the nodes of the underground stems. Plants grown from true seed develop a slender taproot with lateral branches.

The tuber is a modified stem which develops by the swelling of the tip of an underground stem (stolon).

The length of the growing period depends upon cultivar, amount of fertilizer (particularly N), pest attack (particularly the nematode burden on the roots), disease and weather conditions. In South-East Asia, cultivars generally mature in 3-5 months.

Reproductive Biology

The species produces viable seeds and is also capable of regenerating from its underground tubers.

Ecology

To achieve their yield potential potato crops require well-distributed rainfall of 500-750 mm in a growing period of 3-4.5 months. Cropping is possible in drier areas, as in Northern China, but yields are restricted. It can tolerate an annual temperature of 3.6 to 27.8°C, but is a cool weather crop, growing best at 15-20°C for most cultivars (Duke, 1983). Most commercial cultivars of potato tuberize best in cool climates with night temperatures below 20°C. Little or no tuberization occurs at night temperatures above 22°C. Optimum day temperatures for dry matter production are within the range 20-25°C. High light intensities favour dry matter production through their effect on photosynthesis. Short daylengths (12-13 hours) lead to earlier maturity. Potato is tolerant of moderate frost and cool soils (Missouri Botanical Garden Plant Finder, 2014).

In the short daylength conditions of the tropics and subtropics, maximum yields can usually be obtained in cool highland areas and in cooler seasons. In Papua New Guinea, for example, optimum growth of potato takes place at altitudes between 1500 and 2200 m above sea-level, where day temperatures are about 25°C and night temperatures about 20°C.

Potato is tolerant of most soils, except heavy, waterlogged clays. Good drainage is of great importance. Impermeable layers in the soil limit rooting depth and the amount of available water, and so greatly reduce yields. Deep soils with good water retention and aeration give best growth and yields. The species can reportedly grow in a wide variety of soils including sandy loams, silt loams, loams and peats, with a soil pH range of 4.2 to 8.2 (Duke, 1983). Potatoes perform well across a wider range of soil pH than most crops. It is commonly thought that the optimum range is 4.8 to 7.0, but high yields of good quality potatoes are obtained on soils of above 8.0 pH, as on the Wisbech series in Lincolnshire, UK.

In the Americas, S. tuberosum can be grown from sea level up to 4500 m. In Nicaragua the species has been observed at 800-1000 m (Flora of Nicaragua, 2014), while in Panama it has been observed between 1000 and 2000 m (Panama Checklist, 2014). In Antioquia, Colombia, the species has been reported at elevations of 2000-2500 m in Lower Montane Rain Forest (bh-MB) and Lower Montane Wet Forest (Vascular Plants of Antioquia, 2014). In Pakistan the species apparently does well in hilly areas up to 3000 m (Flora of Pakistan, 2014). In Ecuador the species has been reported between 0 and 4500 m (Vascular Plants of Ecuador, 2014), and in Bolivia it has been observed between 2500 and 4000 m and is capable of tolerating dry soil (Bolivia Checklist, 2014).

Diseases of S. tuberosum are numerous and widespread, affecting yield and quality where the plant is grown as a crop. The most prevalent diseases are:

- bacterial diseases, including bacterial wilt caused by Ralstonia solanacearum, bacterial soft rot caused mainly by Erwinia carotivora, and common scab caused by Streptomyces scabies

- fungal diseases including late blight caused by Phytophthora infestans, early blight or target spot caused by Alternaria solani, black scurf caused by Rhizoctonia solani [Thanetophorus cucumeris], and pink rot caused by Phytophthora erythroseptica

- several viral diseases including potato leafroll luteovirus (PLRV) and the mosaic viruses, notably potato X potexvirus (PVX) and potato Y potyvirus (PVY).

Duke (1983) states: In the USA, potatoes are injured by more than 100 species of insects, especially the Colorado potato beetle (Leptinotarsa decemlineata). It and the flea beetle (principally Epitrix spp.) reduce yields by feeding on the foliage. The potato aphid attacks the foliage and also spreads several viral diseases. Potato leaf hoppers cause a destructive disease-like condition known as hopperburn by sucking juices from the plants. The tubers are attacked by wireworms, often rendering the potatoes unsuitable for sale. 

Animal feed, fodder, forage

• Fodder/animal feed

Genetic importance

• Gene source

Human food and beverage

• Beverage base
• Flour/starch
• Vegetable

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical
• Traditional/folklore

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Papers on control of S. tuberosum are generally studies on volunteer potatoes as a weed in succeeding crops. Rahman (1980) reviews the literature on S. tuberosum as a weed, including mechanical, cultural and chemical control methods. Lainsbury et al. (1998) report that clopyralid and ethofumesate reduce the vigour and population density of S. tuberosum in sugarbeet crops. Boydston and Seymour (2002) found that fluroxypyr plus bromoxynil reduced tuber weight of S. tuberosum acting as a weed in onion. Fluroxypyr was found by Riggle et al. (1999) to suppress volunteer S. tuberosum in wheat and barley crops, while Bond (1993) found treatments containing fluroxypyr more effective than ioxynil or clopyralid for control of S. tuberosum in vegetable crops. 

24/8/2014 Updated by:

Marianne Jennifer Datiles, Department of Botany-Smithsonian NMNH, Washington DC, USA

Pedro Acevedo-Rodríguez, Department of Botany-Smithsonian NMNH, Washington DC, USA