tuberosum (Potatoes) DM Spooner, USDA Agricultural Research Service, University of Wisconsin, Madison, WI, USA

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This article is a revision of the previous edition article by K Schuler, volume 4, pp 1848–1850, © 2001, Elsevier Inc.

Glossary Protoplast fusion A nonsexual method of joining genes of Glycoalkaloid A bitter chemical compound with a different organisms by fusing the protoplasts (cell combination of a glycoside and an alkaloid, which is constituents without the cell wall) from different cells. present in potatoes and some other , for example, Rhizome An underground stem, which in potatoes have . tubers positioned at the end. Landrace Native varieties grown by indigenous peoples Sexual hybridization A method of joining genes of that are not improved by modern breeding methods. different organisms through the sexual process, which in Pedigree The breeding history showing the parents of a potatoes and other flowering plants involve transfer of cultivar. pollen (containing male gametes) to styles (containing Ploidy The number of chromosome sets which in female gametes). range from diploid (two sets of 12 chromosomes for a Somatic hybridization A method of joining genes of total of 24), triploid (three sets, 36), tetraploid (four sets, different organisms through any of the variety of 48), pentaploid (five sets, 60), to hexaploid (six sets, 72). nonsexual processes, such as protoplast fusion. Polygenetic A character formed through the interaction of Tuber A thickened and short underground stem having many genes. numerous buds or eyes and used for food storage.

Introduction changed considerably in recent years based on extensive field work and studies on morphology and genetics of collections Potato is the fourth most important food crop worldwide. In obtained from genebanks. Forexample,inamanuscript 2009, the world potato area was 18 651 838 ha, and the amount from 1990 Hawkes states that there were over 220 wild produced was 325 302 445 tons. The major producing countries potato (tuber-bearing species of the huge (as assessed by million tons grown; 2009 data) are China Solanum) and seven cultivated potato species, but recent (73 281 890 million tons), India (34 391 000), Russian estimates are 100–110 wild species and four cultivated Federation (31 134 000), of America (19 569 100), species. and Germany (11 617 500). Potatoes grow under a wide variety Chromosome numbers in wild species vary from diploid − of climates. The potato yield averages 176 702 hg ha 1 worldwide, (2n =2x = 24), triploid (2n =2x = 36), tetraploid (2n =4x = 48), − but varies widely by country, ranging from <40 000 hg ha 1 in pentaploid (2n =5x = 60), to hexaploid (2n =6x = 72). The cul­ − some developing countries to >450 735 hg ha 1 in developed tivated potato has all these ploidy levels, except hexaploid. countries. Cultivated potatoes can be classified as landraces that are The potato is food for both humans and animals, and raw native varieties still grown in South America today, or material for the food processing (e.g., potato chips, French improved varieties that are grown around the world. Potato fries, and dried potatoes) and starch industries. Substantial landraces originated from a group of closely related wild advantages of the potato are its high yield potential in a short species in southern Peru, and were rapidly diffused into two growth time, the high edible dry matter content of its tubers, areas, one group in a broad swath of the upland from and its high dietary value as a staple food. For example, an western Venezuela south to northern Argentina and a second average size raw potato contains only about 115 calories, 3.2 g group in the lowlands of south-central Chile. Our modern of protein, 80 mg of phosphorus, 1 mg of iron, and 30 mg of cultivars that are grown worldwide come from the Chilean vitamin C (about one-half the amount of an average-sized landraces. orange). Boiled potatoes have a similar nutrient composition The edible part of the potato is called a tuber, and is but lose some vitamin C. Baked potatoes contain about 25% actually a modified underground stem, not a root. While tubers more solids and proportionately higher levels of all nutrients of most of the landraces are large, palatable, and grow near the than raw or boiled potatoes. The yield from 0.4 ha (1 acre) of plant, those of many of the wild species are often no larger than potatoes meets both the energy and protein requirements for the size of a pea or hen’s egg and can be quite bitter and over 10 people, with a better balance of nutrients than corn, poisonous due to the presence of chemicals called glycoalka­ rice, wheat, and soybeans. A good balance of essential nutri­ loids. The tubers of the wild species can grow on thin ents is met with supplements of foods high in calcium and underground stems (rhizomes) up to some distance away vitamin A. from the plant, but close to the plant in the cultivated species. Wild potatoes are native from the southwestern United While high concentrations of glycoalkaloids may confer protec­ States to south-central Chile, with centers of species diversity tion against predation in the wild, they are a hindrance to in central Mexico and in the central Andes of Peru and potato breeders, who must ensure that they are greatly reduced Bolivia. The of wild and cultivated potatoes has in advanced cultivars.

Brenner’s Encyclopedia of Genetics, 2nd edition, Volume 6 doi:10.1016/B978-0-12-374984-0.01442-X 481 482 Solanum tuberosum (Potatoes)

History wilt. ‘Virus’–Calico; corky ring spot; roll; mop‐top; PVA; PVM; PVY; PVS; PVX; and rugose mosaic (PVX + PVY). Perhaps 6000 years ago in the Central Andes of what is today For a long period after the potato was introduced into North southern Peru and northern Bolivia, native peoples began to America, little effort was made to improve it or to introduce select wild potato species for human use. According to Hawkes, new kinds. The period from 1719 to 1850 was characterized by who outlined a taxonomic system still used by some today, no marked or lasting improvement in the crop. Improvement there are seven cultivated species: Solanum ajanhuiri (2x), of potatoes near the end of this period became imperative Solanum chaucha (2x), Solanum curtilobum (5x), Solanum juzepc­ because the available cultivars ‘ran out’ to the extent that yields zukii (3x), Solanum phureja (2x), Solanum stenotomum (2x), and decreased to low levels and production was uneconomical. Solanum tuberosum (4x) with the latter containing subspecies ‘Running out’ is caused by increasing levels of andigenum and subsp. tuberosum. However, combined morpho­ tuber-transmitted virus diseases in existing stocks and lack of logical studies of Huamán and Spooner and molecular studies proper seed (potato tuber planting stock) maintenance meth­ of Spooner et al. documented that not all of these seven are ods. In 1851, C. E. Goodrich, a clergyman of Utica, NY, good species, and the current taxonomy by Spooner et al. introduced a small amount of potatoes received from the recognizes only four species: S. tuberosum with Andean and American consulate in Panama. One of them, Rough Purple Chilean landrace groups (Andigenum Group and Chilotanum Chili, was one of the most valuable plant introductions in Group), S. ajanhuiri, S. curtilobum, and S. juzepczukii. The most history and continues to have a tremendous impact on the widely grown landrace is S. tuberosum Andigenum Group and North American potato industry. It contributed 100% of the the other landraces are not as commonly grown. Potato first pedigree of the main US potato cultivar, Russet Burbank, and appeared outside of South America in Europe in 1567 and an average of about 25% of the pedigrees of the 10 most rapidly diffused worldwide. Our modern cultivars of S. tuber­ important cultivars grown in North America. Since 1925, osum originated from the Chilean landraces. The Irish potato plant explorations have been made in the United States, famine caused by potato late blight disease, Phytophthora infes­ Mexico, Central America, and South America in search of new tans, caused widespread famine and migration in Europe wild species and landrace cultivars of potato for use in improv­ beginning in 1845. Late blight remains one of the most serious ing commercial types. In addition, many named cultivars of potato diseases worldwide, but modern breeding and chemical potato have been introduced into genebanks worldwide for use controls afford protection against this disease. in commercial breeding. Potato introductions and their exploitation are especially important because: (1) the potato is the most economically important vegetable in the world, (2) there is a broad array of easily accessible-related Potato Breeding germplasm, (3) solutions to most of the present limitations of the potato have been demonstrated to exist in related germ- The potato is threatened by numerous pests and pathogens, plasm, and (4) potato has a great potential to provide which makes resistance breeding so important. Both the land- nutritious food in a diversity of environments for an increas­ races and wild potato species have been extensively collected ingly hungry world. and are maintained in a series of genebanks worldwide, and are The ability to make crosses between cultivated species and used by potato breeders to incorporate a variety of disease many of the wild species allows use of a vast germplasm resistances as well as traits to improve growth in harsh environ­ resource useful for potato improvement. Although potato has ments such as heat, cold, and drought, and quality traits such as a series of mechanisms that inhibit crossing among many yield or improved potato chipping qualities. Radcliffe men­ cultivated and wild species, these can be overcome to various tions that more than 150 species of insects attack potatoes in degrees by manipulation of chromosome numbers and other North America alone, and Johnson et al. list the following mechanisms that allow widespread germplasm transfer for potato diseases affecting potato in North America alone: breeding programs. Prebreeding at the diploid level makes ‘ ’– bacteria bacterial brown rot, Ralstonia solanacearum; bacterial the interpretation of genetic segregation and selection of poly­ soft rot, Pectobacterium carotovorum var. carotovora; blackleg, genetic traits easier. Besides the classic sexual hybridization, Pectobacterium carotovorum var. atrosepticum; common scab, there is the possibility of combining genomes asexually by Streptomyces scabies, Streptomyces spp.; and ring rot, Clavibacter protoplast fusion. This somatic hybridization can be applied michiganensis subsp. sepedonicus. ‘Chromista’ – late blight, to species that are impossible or very difficult to cross sexually ; leak, Pythium debaryanum, Pythium spp.; (e.g., S. bulbocastanum � S. tuberosum subsp. tuberosum). and pink rot, Phytophthora erythroseptica, Phytophthora spp. ‘’–blackdot, Colletotrichum coccodes; dry rot, Fusarium See also: spp.; early blight, solani, Alternaria alternata; Fusarium Somatic Mutation. wilt, Fusarium solani var. eumartii, Fusarium oxysporum; Rhizoctonia, Rhizoctonia solani; silver scurf, ; Verticillium wilt, Verticillium spp.; and white mold, Further Reading Sclerotinia sclerotiorum. ‘Nematode’– Columbia root knot, Meloidogyne chitwoodi; golden, Globodera rostochiensis; potato Ames M and Spooner DM (2008) DNA from herbarium specimens settles a controversy tuber rot, Ditylenchus destructor; root knot, Meloidogyne spp.; about origins of the European potato. American Journal of Botany 95: 252–257. Emsinger AH, Emsinger ME, Konlande JE, and Robson JRK (1994) Foods & Nutrition and poot lesion or meadow, Pratylenchus penetrans. Encyclopaedia, 2nd edn. Boca Raton, FL: CRC Press. ‘Plasmodium’–powdery scab, Spongospora subterranean, and Food and Agriculture Organization (FAO) (2009) FAOSTAT. http://faostat.fao.org wart, . ‘Phytoplasma’– purple‐top (accessed 12 October 2011). Solanum tuberosum (Potatoes) 483

Hanneman RE, Jr. (1989) The potato germplasm resource. American Potato Journal 66: Spooner DM (2009) DNA barcoding will frequently fail in complicated groups: An 655–667. example in wild potatoes. American Journal of Botany 96: 1177–1189. Hawkes JG (1990) The Potato: Evolution, Biodiversity and Genetic Resources. London: Spooner DM (2010) Botany of the potato; morphology and anatomy; plant Belhaven Press. introduction and maintenance. In: Bohl WH and Johnson SB (eds.) Commercial Hijmans RJ and Spooner DM (2001) Geographic distribution of wild potato species. Potato Production in North America,2nd edn.,pp. 4 –7. The Potato Association of American Journal of Botany 88: 2101–2112. AmericaHandbook,Supplement,Vol.57ofUSDAHandbook267.Orono,ME: Huamán Z and Spooner DM (2002) Reclassification of landrace populations of cultivated The Potato Association of America. http://potatoassociation.org/documents/ potatoes (Solanum sect. Petota). American Journal of Botany 89: 947–965. A_ProductionHandbook_Final.pdf Jansky SH (2000) Breeding for disease resistance in potato. Plant Breeding Reviews Spooner DM, McLean K, Ramsay G, Waugh R, and Bryan GJ (2005) A single 19: 69–155. domestication for potato based on multilocus AFLP genotyping. Proceedings Johnson SB, Stevenson W, and Miller J (2010) Disease control. In: Bohl WH and of the National Academy of Sciences of the United States of America 102: Johnson SB (eds.) Commercial Potato Production in North America, 2nd edn., 14694–14699. pp. 67–72. The Potato Association of America Handbook, Supplement Vol. 57 of Spooner DM, Núñez J, Trujillo G, et al. (2007) Extensive simple sequence repeat USDA Handbook 267. Orono, ME: The Potato Association of America. http:// genotyping of potato landraces supports a major reevaluation of their gene pool potatoassociation.org/documents/A_ProductionHandbook_Final.pdf structure and classification. Proceedings of the National Academy of Sciences of the Ortiz R, Simon P, Jansky S, and Stelly D (2009) Ploidy manipulation of the gametophyte, United States of America 104: 19398–19403. endosperm, and sporophyte in nature and for crop improvement: A tribute to Prof. Stanley J. Peloquin (1921–2008). Annals of Botany 104: 795–807. Radcliffe EB (2010) Insect control. In: Bohl WH and Johnson SB (eds.) Commercial Relevant Websites Potato Production in North America, 2nd edn., pp. 64–67. The Potato Association of America Handbook, Supplement Vol. 57 of USDA Handbook 267. Orono, ME: The Potato Association of America. http://potatoassociation.org/documents/ http://cipotato.org – International Potato Center. A_ProductionHandbook_Final.pdf http://www.ars-grin.gov – NRSP-6: United States Potato Genebank.