Potato is a starchy, tuberous crop from the perennial night shade solanum tubersum L. The word potato may refer to the plant itself or the edible tuber. Potatoes were introduced outside the Andes region approximately four centuries ago (1) and since become an integral part of much of the World’s food supply. It is the World’s fourth largest food crop, following maize, wheat and rice (2).
Through centuries of selective breeding, there are now over a thousand different type of potatoes (3).Over 99% of the presently cultivated potatoes worldwide descended from varieties that originated in the low lands of South-central Chile, which have displaced formerly popular varieties from the Andean highlights (4) (5).
The annual diet of an average person in the first decade of the 21st Century included about 33kg (73Ib)of potatoes (2).China is now the world largest potato producing country and nearly a third of the world’s potato are harvested in China and India (6).
Total geographical area of Pakistan is 79.6 million hectare, ranging from great Himalayas to fertile Indus basin and deserted areas in Sindh and Baluchistan. Out of this total area, only 24.6 million hectare is under cultivation including 4.2 million hectare covered with forest. Remaining area account for deserted mountainous and barren land. Irrigated area is 18 million hectare, while 6.6 million hectare is subjected to natural arid environmental conditions, completely depending upon natural precipitation to meet the crop irrigation requirement. (7).
Potatoes in Pakistan are produced under eight ecological zones these are.
1. Irrigated plains of Sindh, Southern Punjab and Baluchistan.
2. Irrigated plains of central Punjab and South East NWFP.
3. Irrigated and rain fed plains of NWFP and northern Punjab.
4. Irrigated lower valley of NWFP.
5. Rain fed high valleys of hill sides of NWFP, Northern Punjab and Azad Kashmir.
6. Irrigated high valley of NWFP, Northern area around Chillas and Azad Kashmir.
7. Irrigated high valley of northern areas and NWFP around Mastuj.
8. Irrigated high valley of Baluchistan, south and North Waziristan (8) (9).
Manor potato producing district in Punjab are Okara, Sahiwal, Kasur, Sialkot, Sheikhupura, Narwal, Lahore, Pakpattan, Jang, toba Tek Singh and Gujranwala in KPK are Nowshera, Dir and Mansehra in Baluchistan are Pishin, Kila Soaifulla and Kalat. (7).
Potato crop yield are determined by factors such as the crop breed, seed age , quality, crop management practices and the plant environment, improvement in one or more of these yield determinants and closure of the yield gap, can be a major boost to food supply and farmer income in developing world (10) (11).
Newzealand farmers have demonstrated some of the best commercial yields in the world, ranging between 60-80 tonnes/hectares, some reported 88 tonnes/hectare (12) (13) (14). In Pakistan per hectare is yield is 19.34 tonnes, which is about 45.66 tones lower than that of developed countries such as USA and Holland where average per hectare yield is 65 and 45.5 tonnes respectively (7)
In the year 2011-12 the area under potato production was 184.9 per (000, hectare) and % share was 30.2. While the production of potato for the same year was 3392.5 (000, tonnes) and % share was 40.0 (15). In Punjab the potato production share % was 95.4, in Sindh it was 0.1 and KPK was 3.5 and Baluchistan was 1.0 (15).
Around 279,000 metric tonnes potato worth 6872 million rupees were exported during 2011-12 as against 426,000 metric tonnes worth 8492 million rupees during 2010-11. There was decline of 19% value wise. One of the reasons for the un-precedent hike in potato export in 2010-11 was the shortage of potato in Russia. Potato exported 117,000 tonnes of potato to Russia in 2010-11. The figure dropped to roughly 20,000 tonnes in 2011-12. Potato fresh and frozen export 2011-12 was 279313 tonnes worth 6872 million rupees (15).
Potato export ( fresh and chilled) from Pakistan to Afghanistan, Bahrain, Brunei, Burma, Cambodia, china, Dubai, Hong Kong, India, Kuwait, Malaysia, Maldives island, Newzeland , Norway, Qatar, Saudi Arabia, Singapore, South Korea, Spain, Sri Lanka, sultanate of Oman and USA (16).
Potato plants are herbaceous perennials that grow about 60 cm (24 inches) high, depending upon variety. With the culms drying back after flowering. They bear white, pink, red, blue or purple flowers with yellow stamens. In general, the tubers of varieties with white flowers have white skin, while those of varieties with colored flowers tend to have pink skin (17).
Potatoes are mostly cross-pollinated by insect such as bumblebees, which carry pollen from other potato plant through a substantial amount of self-fertilizing occurs as well. Tubers form in response to decreasing day length, although this tendency has been minimize in commercial varieties (18).
Potato fruit contains large amount of toxic alkaloid Solanine and therefore un-suitable for consumption. New potato varieties are grown from seed so called “true-seed” or “botanical seed” to distinguish it from seed tubers.
Any potato variety can also be propagated vegetative by planting tubers , pieces of tubers cut to include at least one or two eyes or cuttings, a practice used in green houses for the production of healthy seed tubers.
Some commercial varieties do not produce seeds at all as they bear imperfect flowers, and are instead propagated only from tubers pieces. These tubers or tuber prices are called “seed potatoes” because the potato itself functions as seed.
Recent study suggests that Flavonoids antioxidants and querceton present in potato tubers have anticancer and cardio protective properties and protect the body from infectious agents and scavenge harmful, pro-inflammatory free radicals (7).
There are 4000 different varieties of potatoes (19). The varieties differ due to comparative ratio of two potato starch compounds. Amylase and Amylopectin (20)
In Pakistan both white and red skin varieties are cultivated but red skin are mostly liked by consumers. Red skin varieties include Desiree, asterix, lady roseta, Krouda, rodeo, cardinal, ultimas, lal-e-faisal and simphonia while diamante, Santana, ajax, patrones, multa and santé are white skin varieties being cultivated commercially (7).
In Sindh mean annual temperature is 25-30 0C.Mean annual rainfall range 100-125 mm. It has subtropical with hot summer and mild winter, while potato require 250C temperature for germination and 20 0C for vegetative and 16-19 0C for tuber formation (7).Potato prefer loamy and sandy loam soil that rich in organic matter. Soil pH 5.2-6.4 considered ideal (21).
Copper used 6 kg/ha/year to control phytophthora infestans (22).It may require Monitor (1 spray of 500 ml) and Imedacleparid (1 spray of 200 grams and fungicide spray of Dithane-M, Intracol and Ridonal as well as weedicide sprays. It also require 3 bags of DAP (50kg bag), 4 bags of urea (50 kg bag) and 3 bags of SOP (50 kg bag) per hectare (16) .It is suggested that precautionary sprays of fungicide in the month of November for autumn crop. In February for spring crop and in August for summer crop, can save the crop from severe damage of late blight (21).
For spring crop, planting time is January-February and harvesting in April-May and it have 07-10% production share, in summer crop, planting time is March-May and harvesting in August-October, it have 15-20% production share, while in autumn , planting time is September-October, harvesting takes place in January-February and it have 70-75% production share (8).For potato crop maturation needs 120-150 days, usually two tonnes of seed potato are sown per hectare(21).
Potatoes are generally grown from seed potatoes- these are tubers specifically grown to be disease free and provide consistent and healthy plants. It require cold winter that kill pest and long sunshine hours in summer for optimum growth. Potato growth has been divided in to five phases. During the first phase, sprouts emerge from the seed potatoes and root growth begins. During second phase, photosynthesis begins as the plant develops leaves and branches in the third phase stolons develop from lower leaf axils on the stem and grow downwards in to the grounds and on these stolons, new tubers develop as swellings of the stolons. This phase is often (but not always) associated with flowering tubers formation halts when soil temperature reach 270C (81 0F); hence potato are considered as cool season crop (23).
Tuber bulking occurs during the fourth phase, when the plant begins investing the majority of it resources in its newly formed tubers. At this stage, several factors are critical to yield: optimum soil moisture and temperature, soil nutrient availability and balance, and resistance to pest attack. The final phase is maturation, the plant canopy dies back, the tubers skin harden and their sugars convert to starch (24).
Good ground preparation, harrowing, plowing and rolling are always needed along with the little grace of weather. It requires 500-700mm (20-27.5 inches) of water. In potato they are grown from the eyes of another potato and not from seed. Commercial growers plant potatoes as a row crop using seed tubers, young plants or micro tubers and may mound the entire row .Seed potato crops are “rouged” in some countries to eliminate disease plants or those of a different variety from the seed crop.
There are 5,000 potato varieties worldwide 3000 of them are found in the Andes alone, mainly in Peru, Bolivia, Ecuador, Chile and Colombia. They belong to eight or nine species, depending upon the taxonomic school. A part from 5000 cultivated varieties, there are about 200 wild species and subspecies, many of which can be cross-bred with cultivated varieties. Cross breeding has been done repeatedly to transfer resistance to certain pest and disease from the gene pool of wild species to the gene pool of cultivated potato species. Genetically modified varieties have met public resistance in the united state and in the Europe union. (25) (26).
The major species grown worldwide is Solanum tuberosum (a tetraploid with 48 chromosomes) and modern variety of this species is most widely cultivated. There are also four diploid species (with 24 chromosomes) S. Stenotomum, S. Phureja, S.gonicalyx and S.ajanhuiri. There are two triploid species (with 36 chromosomes): S. chaucha and S.Juzephezukii. There is one pentaploid cultivated species (with 60 chromosomes). S. Curtilobum. There are two major subspecies of Solanum tuberosum: andigena or Andean and tubersum or Chilean (27).
The Andean potato is adapted to short-day conditions prevalent in the mountainous equatorial and tropical regions, where it is originated, the Chilean potato however native to the Chiloe Archipelago, is adapted to long-day conditions, prevalent in the higher latitude region of South Chile (28).
International potato center based in Lima, Peru hold and ISO accredited of potato germplasm (29).International potato genome sequencing consortium announced in 2009 that they have achieved a draft sequence of the potato genome (30) .The potato genome contain 12 chromosomes and 860 million base pairs, making it a medium-sized plant genome (31).More than 99% of all current varieties of potatoes currently grown are direct descendants of a subspecies that once grew in the low bank of South-Central-Chile (32)
Nonetheless, genetic testing of the wide variety of cultivars and wild species affirms that all potato subspecies derived from a single origin in the area of present day Southern Peru and extreme northwestern Bolivia ( from species in the Solanum brevicaule complex (33) (34) (35).
Solanum fendieri is used in breeding for resistance to a nematode species that attacks cultivated potatoes. Hexapoloid solanum demissum is used as a source of resistance to the devasting late blight disease (36). Solanum bulbocastanum has been used to genetically engineer the potato to resist potato blight (37).
The potato contains vitamins and minerals as well as assortment of phytochemcals, such as carotenoids and natural phenols. Chlorogenic acid constitute up to 90% of potato tuber natural phenol. Other found in potato are 4-o-Caffeoylquinic acid (Crypto-chlorogenic acid), 5-o-Caffeoylquinic (neo-chloro-genic acid), 3, 4-dicaffeoyliquinic and 3, 5-Caffeolyquinic acid (38).
A medium size 150g( 5.3 oz) potato with the skin provides 27 mg of Vitamin C( 45% of the Daily Value (DV), 620 mg of potassium (18% of DV) 0.2 mg of Vitamin B6 ( 10% DV) and trace amount of thiamine, riboflavin, foliate, niacin, magnesium, phosphorus , iron and zinc. The content of potato with skin (2g) is equivalent to that of many whole grain bread, pasta and cereals.
It contains carbohydrates (26g of medium potato). The predominate form of the carbohydrate is starch. A small but significant portion of this starch is resistant to digestion by enzyme in the stomach and small intestine, so reaches the large intestine essentially intact. The resistant starch is considered to have similar physiological effects and health benefits as fiber. It provides bulk, offer protection against colon cancer, improve glucose tolerance and insulin sensitivity, lower plasma cholesterol and triglyceride concentration, increase satiety and possible even reduces fat storage (39) (40) (41). Potato is high on glycemic index (GI).
Potato contain toxic compound known as glycol-alkaloids, of which the most prevalent are Solanine and Chaeonine. T This toxic effects in the nervous system, causing weakness and confusion. The higher concentrations occur just underneath the skin. Cooking at high temperature over 170 0C (340 0F) partly destroy these glycol-alkaloids may cause headache, diarrhea, cramps and sever cases coma and death. Poisoning from potato very rarely.
Breeders try to keep Solanine level below 200 mg/kg (200 ppmw), when these varieties turn green they can approach concentration of Solanine 1000 mg/kg (1000 ppmw). In normal potatoes analysis has shown Solanine level may be as little as 3.5% of the breeder’s maximum, with 7-187 mg/kg being found (42).While normal potato has 12-20 mg/kg of glycol-alkaloid content, a green tuber contains 250-280 mg/kg and green skin 1500-200 mg/kg (43).
Cold weather makes potatoes more susceptible to bruising and possibly latter rotting, which can quickly run a large stored crop. It is commercially harvested with large potato harvesters. Potatoes are usually cured after harvest to improve skin-set. Skin-set is a process by which the skin of potato becomes resistant to skinning damage. Potato tubers may be susceptible to skinning at harvest and suffer skinning damage during harvest and handling operation. Curing allow the skin to fully set and any wound to heal. Wound healing prevents infection and water loss from the tubers during storage. Curing is normally done at relatively warm temperature 50-60 0C (122-140 0F) with high humidity and good gas exchange if at all possible (44).
Potato long-term storage maintained at temperature 4 0C (39 0F). For short term storage before cooking maintained at temperature 7-10 0C (45-50 0F) (45) (46). Temperature below 4 0C (39 0F) convert potatoes “starch in to sugar”, this lead to higher acryl amide level in the cooked product. This is possibly carcinogens and cause health problem (47).
Under optimum conditions, potato can be stored up to 10-12 months. When stored in home the shelf life is only few weeks (46). Commercial storage of potatoes involve several phases, drying of surface moisture, a wound healing phase at 85 to 95% relative humidity and temperature below 25 0C( 77 0F),a stage cooling phase; a holding phase, and a reconditioning phase, during which the tubers are slowly warmed. Mechanical ventilation is used at various points during the process of to prevent condensation and accumulation of carbon di oxide (45).
The gene Bacillus thuringiensis, which confer resistance to the Colorado potato beetle, so they developed “New leaf plus” and “New leafy” also resistance to virus developed in USA (48). Waxy potato varieties produce two main kinds of potato starch amylose and amylo pectin. So in Germany create Amflora potato, which has been modified contain antisense against the enzyme that derives synthesis of amylase, namely granule bound starch synthase (49). This resulting potato exclusively produces amylopectin.
Genetically modified potato variety “Fortuna” which was resistant to late blight by adding resistance gene bib1 and bib2 (50) (51). India have developed genetically modified potato by adding gene AmA1 from the grain Amaranth and it gives 15-25% greater crop yield having 35-60% more protein (52).
USDA developed “Innate potatoes” which contains 10 genetic modifications that prevent bruising and produce less acrylamide when fried than conventional potatoes, the inserted genetic material comes from cultivated or wild potatoes and lead to RNA interference which prevents certain protein from being formed (53) (54) (55).
In Pakistan using the genetic engineering technique and Rp1-Vnt 1.1 gene from Solanum venturrii has been introduced in commercial variety “Desiree” as this gene confers resistant to Phytophthora infestans (late blight).
In USA potato grading for Idaho potatoes is performed in which No.1 potatoes are highest quality. No.2 is related as low in quality due to their appearance (e.g. blemishes or bruises pointy ends (56). Potato density assessment can be performed by floating them in brine (57). High density potatoes are desirable in the production of dehydrated mashed potatoes, potato crisps and French fries (57).
There are many insects and pest attack on potatoes; some of them are as under:
• Phytophthora infestans (late blight).
• Rhizoctonia, sclerotinia, black leg, powdery mildew, scab and leaf roll virus.
• Insect’s e.g. Colorado potato beetle, potato tuber moth.
• Green peach aphid (Myzus persicae) potato aphid, beet leafhopper, thrips, mites and potato root nematode.
• In Pakistan the most common 13 infection are: early blight, late blight, powdery mildew, common scab, stem rot, soft rot and wilt caused by Alternaria Solani, Phytopathora infestans, Erysiphe Ciehoracearum, streptomyces, scabies, Erwinia Caroto vora spp. Carotovora, and Fussarium spp. And Verticillium dahlia.
• Potato virus includes virus X, potato virus Y, potato leaf roll virus and potato mop top virus.
• Major insect and pest attacking include green peach aphid (Myzus persicae), cutworm (Agrotis spp.) Colorado potato beetle, white grub (Phyllophaga spp), white worm (Elateridae spp).Potato cyst nematode (Heterodera rostochiensis) and root knot nematode (Meloidogyne incognita) hamper root and tuber formation.
• White fly is the major vector potato viral disease.(7)
• Disease with Mycoplasma pathogen results in to 45% reduction in yield.
• Soil borne disease cyst nematode, Rhizoctonia, verticillium, scab and sotrot.
Potato has many uses like:
• Potatoes are used to brew alcoholic beverage.
• Potatoes are used as food for domestic animals.
• Potato starch is used in food industry e.g. thickeners and binder of soup and sauces, in the textile industry as adhesives and for the manufacturing of papers and board (58) (59).
• Waste potatoes are used to obtain Polyactic acid for use in plastic products also used in biodegrading packaging (59) (60).
• Potato skins, along with honey are folk remedy for burns in India (61) (62).
• Potatoes (mainly russets) are commonly used in plant research. The consistent parenchyma tissue, the clonal nature of the plant and low metabolic activity provide a very nice “model tissue” for experimentation. Wound response studies are often done on potato tuber tissue, as are electron transport experiments.
• Culinary uses- potatoes are prepared in many ways, skin on or peeled, whole or cup-up, with seasoning or without. The only requirement involves cooking to swell the starch granules. Most potato dishes are served hot but some are first cooked then serve cold, notably potato salad and potato chips/crisp. Most common dishes are mashed potato, potato boiled, potatoes are boiled between 10 to 25 minutes depending on size and type to become soft (63).
Conclusion
In Pakistan the potato yield and production is much lower than the Developed countries. This is due to
• Lack of adequate storage facilities.
• Under develop processing industry.
• Lack of high yielding and disease resistant clone.
• No proper gene pool is available in the country.
• Lack of coordination in seed producing agencies.
• Little public-private seed producer cooperation exists.
• Tissue culture laboratory produce limited quantities of Caroda, Santee, burna, easterix, Desiree, cordinal and diamante of plants, which not full fill the domestic needs.
• Few mechanical harvesters are available.
• Poor market infrastructure.
If we overcome above shortages than Pakistan can attain the higher yield and production and compete the world.
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