Crops - Potatoes
Potato Breeding
Potato is the fourth most important food crop in the world after wheat, rice and maize, and the area under production worldwide is rising faster than that of any other crop due to its high yield potential and excellent nutritional characteristics. Potato is of particular importance in Ireland where it is still the primary carbohydrate source at main meals, whereas bread, pasta and rice tend to be the main sources in the rest of Europe. The potato breeding programme at Teagasc, Oak Park, Carlow, commenced in 1962. The original objective was to breed a high-yielding, late blight- (Phytophthora infestans) resistant variety for the Irish market to replace the traditional varieties such as Kerr’s Pink and Record.
With the introduction of plant breeders’ rights in the 1970s, increased demand for export varieties was experienced and the aims of the programme quickly diversified. A partnership was formed soon after with Irish Potato Marketing to exclusively market Teagasc varieties, which has led to commercial success and stability for one of the organisation’s longest running funded programmes. The introduction and subsequent success of the Cara variety secured the future of potato breeding at Oak Park. Cara was grown widely in Ireland, mainly for seed export and, at the height of its success, it accounted for over 10% of the total ware area (for consumption) in the UK. Over 30 varieties have been released in the intervening period, with eight of these (Camelot, Galactica, Kikko, Setanta, Habibi, Nectar, Carnaval and Savanna) in the last five years. Rooster is the best known of the Oak Park varieties due to its status as the most popular potato variety in Ireland. Since its release in 1991, the area under production has grown to over 40% of the total potato ware area in Ireland today. The success of Rooster is due largely to its excellent taste and cooking quality, as well as its superior agronomic characteristics.
Today, varieties are bred for the home market, for export trade and for the processing industry. The breeding process for potatoes can take up to 15 years, from initial crossing to delivery and commercialisation of a new variety. This means that breeders must predict the traits that will be important in 15 to 20 years time to meet demand and ensure the success of new varieties. The important traits for potato have changed over the years. Flavour and texture were once considered the most important attributes. The advent of washed potato displays in supermarkets require varieties that also exhibit good tuber shape and uniformity, smooth unblemished skin texture and shallow eyes. The consumption of fresh potatoes is also falling, with more potatoes being consumed as fried or processed product. Specialist varieties with low reducing sugar content are required for this processing market. The potato is susceptible to a wide range of pests and diseases, many of which cause serious yield penalties (late blight, blackleg and potato cyst nematode), with others that affect skin quality and marketability (common scab, black scurf and silver scurf). While chemical control is available for many of these diseases, this approach is becoming less favoured by consumers and regulators. Many novel disease resistance traits are available in wild relatives of the cultivated potato, and introgression of these traits by conventional methods has been very successful over the last 30 years, leading to increased disease resistance in many new varieties. This has the ability to lower pesticide inputs and could have a significant role in organic production systems. Breeding late blight- and potato cyst nematode-resistant varieties will continue to be a major goal in the future. Potato agronomy and crop husbandry techniques have also improved dramatically, and these systems require new varieties with superior phenotypes to fully exploit their yield and quality potential. Already, demand is increasing for varieties that require reduced inputs of water and nitrogen and that mature earlier in the season, allowing harvesting to take place before soils become wet and susceptible to damage.
Reproduction of the commercial potato crop is by clonal propagation. Each potato tuber planted is an exact genetic copy of the plant it was derived from. Potato breeding takes advantage of the production of true botanical potato seed, which exhibits high levels of genetic variation. New potato varieties are produced by combining the best characteristics from selected parents that have complementary traits. Varieties to be used as parents are grown in the glasshouse. Potato flowers possess both male and female sex organs. Flowers selected for use as females have the male anthers removed prior to maturity in a technique known as emasculation; this technique ensures that self-fertilisation cannot take place. When these flowers mature, pollen is harvested from mature whole flowers of the selected male parent and used to fertilise the emasculated flower. If fertilisation is successful, a berry will form. Potatoes and tomatoes are very closely related and the potato berry resembles a small green tomato. One berry can contain up to 200 seeds, each of which is a genetically different individual representing a potential new variety. Up to 100,000 true seeds are grown for evaluation each year in pots. Each seed produces a number of tubers, only one of which is retained for propagation in the field as single spaced plants. These seedlings are visually selected at the end of the first field season for commercial traits and only 3,000 are advanced for further evaluation. Seedlings are tested for a further eight years in the field under increasingly rigorous selection criteria. The numbers are reduced each year as more traits are scored, beginning with foliage maturity in year four and culminating with disease resistance screening, organoleptic evaluation and agronomic performance across a number of geographically diverse sites representing countries where the variety might eventually be grown.
After approximately 10 years of evaluation, only one to two seedlings remain, which are entered for national list trials to determine if they are suitable for variety status and a grant of plant breeders’ rights. The future aims of the programme are to continue to produce agronomically superior, disease-resistant varieties, with excellent taste and consumer attributes. The traditional breeding process is constantly being re-evaluated and updated to incorporate cutting-edge technologies, such as marker assisted selection (see TResearch Winter 2006; 1 (1): 28) in collaboration with the Plant Biotechnology Unit at Oak Park. The discovery of new markers and genes through Teagasc’s involvement with the potato genome sequencing project will make the process of introgressing resistance traits more efficient.
