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Advances in Potato Chemistry and Technology
Academic Press
Copyright © 2009 Elsevier Inc.
All right reserved.
ISBN: 978-0-08-092191-4
Chapter One
Potato Origin and Production John E. Bradshaw Gavin Ramsay
SCRI, Invergowrie, Dundee DD2 5DA, UK
1.1 Introduction
The potato (Solanum tuberosum) is the world's fourth most important food crop after wheat, maize and rice with 314 million tonnes fresh-weight produced in 2006 (FAOSTAT). Over half of this production (159 million tonnes) was in Asia, Africa and Latin America where the potato is a major carbohydrate (starch) supplier in the diets of hundreds of million of people. It also provides significant amounts of protein, with a good amino acid balance, vitamins C, B6 and B1, folate, the minerals potassium, phosphorus, calcium, and magnesium and the micronutrients iron and zinc. The potato is high in dietary fiber, especially when eaten unpeeled with its skin, and is rich in antioxidants comprising polyphenols, vitamin C, carotenoids and tocopherols (Storey, 2007). Fresh potatoes are virtually free of fat and cholesterol. A guide to potato composition is shown in Table 1.1, but it must be appreciated that values are affected by both cultivar and growing conditions.
As a major food staple the potato is contributing to the United Nation's Millennium Development Goals of providing food security and eradicating poverty. In recognition of these important roles, the UN named 2008 as the International Year of the Potato. Food security and eradicating poverty are high on the agenda of the International Potato Center (CIP) in Lima, Peru. CIP was founded in 1970 as an international agricultural research center (IACR), and is now a Future Harvest Center. Since 1971, CIP has been supported by the Consultative Group on International Agricultural Research (CGIAR), whose aim is the eradication of human hunger and poverty through research. Eradicating poverty is helped where the potato provides not only food but also employment and income as a cash crop.
As a staple food and as a vegetable for table use, the potato needs to be cooked because of the indigestibility of its ungelatinized starch (Burton, 1989). Such cooking is frequently by baking, boiling, steaming, roasting, deep-fat frying or microwave cooking, although in the Andes a broad diversity of additional preparation methods are employed. Good appearance, texture and flavor are important to the consumer and the subject of much research (Taylor et al., 2007). When baked, boiled or mashed and eaten alone, potatoes generally have a high glycemic index (GI), like other staple starchy foods such as some types of rice and white bread (Foster-Powell et al., 2002). However, boiled waxy or new potatoes, and potatoes prepared in different ways, have lower GI values and so carry reduced concern for diabetics (Henry et al., 2005). Eating potatoes in mixed meals will further alter GI levels, and the nutritional benefits of potato indicate that they are generally a useful and nutritionally beneficial component of the human diet (McGregor, 2007).
The potato is processed into French fries (chips in the UK) and chips (crisps in the UK), and is used for dried products and starch production. In North America and some European countries between 50 and 60% of the crop is processed (Li et al., 2006; Kirkman, 2007). Furthermore, processors are building factories in countries where the potato is primarily grown as a staple food, and this is a trend that is likely to continue. Kirkman (2007) has estimated that global consumption in processed form will have increased from 13% of total food use in 2002 to nearly 18% by 2020. In some countries the potato is still fed to animals but this use is decreasing.
Potatoes were grown on 19.6 million hectares of land in 2006 (FAOSTAT), in 149 countries from latitudes 65°N to 50°S, and at altitudes from sea level to 4000 m (Hijmans, 2001). Potato production by region is shown in Table 1.2 and consumption by region in Table 1.3. The four largest potato producers are China (70 million tonnes), the Russian Federation (39 million tonnes), India (24 million tonnes) and the USA (20 million tonnes) with per capita consumption still much larger in Russia than in the other countries. Potatoes can be grown wherever it is neither too hot (ideally average daily temperatures below 21°C) nor too cold (above 5°C), and there is adequate water from rain or irrigation (Govindakrishan and Haverkort, 2006). In practice this means that they are grown as a summer crop in the tropical highlands of Bolivia, Peru and Mexico, all the year round in parts of China and Brazil and in the equatorial highlands of South America (e.g., Ecuador and Colombia) and East Africa (e.g., Kenya and Uganda), as a winter crop in the lowland subtropics (e.g., northern India and southern China), as spring and autumn crops in the Mediterranean (e.g., North Africa), and in summer in the lowland temperate regions of the world (North America, western and eastern Europe, northern China and Australia and New Zealand).
The growing season can be as short as 75 days in the lowland subtropics, where 90–120 days is the norm, and as long as 180 days in the high Andes. In the lowland temperate regions where planting is done in spring and harvesting in autumn, crop duration is typically 120–150 days, and yields are potentially high. Average fresh-weight yields vary tremendously by country from 2 to 45 t/ha with a global average of 16.1 t/ha in 2006 (FAOSTAT). As potatoes cannot be grown year round in most parts of the world, it is normal to have to store both seed tubers for planting the next crop and ware tubers for consumption. Hence post-harvest infrastructure in terms of road transport and cold storage facilities is also an important aspect of potato production.
This opening chapter provides a brief introduction to the origin of the potato and its transformation into a crop that makes a major contribution to the feeding of humankind. The following books proved useful sources of information and references: The Potato (Burton, 1989), The Potato Evolution, Biodiversity and Genetic Resources (Hawkes, 1990), Handbook of Potato Production, Improvement, and Postharvest Management (Gopal and Khurana, 2006), Potato Biology and Biotechnology Advances and Perspectives (Vreugdenhil, 2007) and Propitious Esculent (Reader, 2008).
1.2 Potato Origin
1.2.1 Wild tuber-bearing Solanum species
Wild tuber-bearing Solanum species are distributed from the southwestern United States (38°N) to central Argentina and adjacent Chile (41°S) and cover a great ecogeographical range (Hawkes, 1990; Spooner and Hijmans, 2001). In the southwestern USA and in Central America wild species generally occur at medium to high altitudes. In South America they are found along the Andes from Venezuela to northwest Argentina and also in the lowlands of Chile, Argentina, Uruguay, Paraguay and southeastern Brazil. The adaptive range among the different species is very great and includes the high Andean regions from 3000 m to the vegetational limit at 4500 m where frosts are common, dry semi-desert conditions and scrub and cactus deserts, cool temperate pine and rain forests, woodlands and coastal plains. Wild species have also developed resistances to a wide range of pests and diseases. Hence they are a tremendous resource for potato breeding and research for which purposes it is important to appreciate their wide geographical distribution and great range of ecological adaptation (Hawkes, 1994). There have been numerous collecting expeditions, from those pioneered by the Russians in the 1920s (Hawkes, 1990) to the more recent ones of the 1990s (Spooner and Hijmans, 2001). The germplasm is maintained in a number of genebanks around the world which together comprise the Association for Potato Intergenebank Collaboration (http://www.potgenebank.org).
The taxonomy of wild tuber-bearing Solanum species is complicated and under continuous revision. Hawkes (1990) recognized 219 wild tuber-bearing species and arranged them into 19 series of subsection Potatoe of section Petota of subgenus Potatoe of genus Solanum (Table 1.4). He grouped series I to IX in superseries Stellata and series X to XIX in superseries Rotata. He considered the sequence of subsections, superseries and series to reflect an approximate evolutionary one and suggested a possible scenario for the evolution of wild potato species, while acknowledging that modification may be required as a result of continuing experimental work particularly with molecular markers. He also recognized a further nine closely related non-tuber-bearing species that he grouped into two series of subsection Estolonifera, but these have been excluded from section Petota in more recent taxonomic reviews, leaving a section comprising all tuber-bearing species (Spooner and Salas, 2006).
Spooner and Hijmans (2001) reviewed accepted species based on a literature survey, including new species described and names placed in synonymy since Hawkes' treatment, and listed 196 wild tuber-bearing species. Further changes in the delimitation of species are being reported as molecular marker and DNA sequence data are used to clarify species relationships. The latest summary by Spooner and Salas (2006) recognizes 188 wild potato species for section Petota that are grouped into four clades, based on plastid DNA, rather than 19 series (Table 1.4). Clade 1 comprises the US, Mexican and Central American diploid species, exclusive of S. bulbocastanum, S. cardiophyllum and S. verrucosum; Clade 2 comprises S. bulbocastanum and S. cardiophyllum; Clade 3 comprises all examined members of the South American series Piurana and some South American species classified to other series; and Clade 4 comprises all remaining South American species and the US, Mexican and Central American polyploid species and S. verrucosum. However, this plastid-based classification splits similar species into different clades and so may not properly represent groupings made on the basis of nuclear DNA. Furthermore, it is not an appropriate means of classifying allopolyploid groups. The number of species may be further reduced in the future, and clade composition based on chloroplast DNA may change as extensive nuclear DNA sequence data become available. Of more interest to potato breeders is the origin and relatedness of the genomes in wild and cultivated potatoes, including hybrid taxa, and their accessibility for breeding via crossing.
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