True Potato Seed (TPS)

Potato is an inalienable part of our food habit. Due to limitations in flowering, complex ploidy level and non uniformity in sexual offsprings cultivation of potato through asexual reproduction became popular.

Potato (Solanum tuberosum) is generally propagated through tuber pieces, commonly known as seed tuber. But like other solanaceous crops viz. tomato, brinjal and chilli, Potato do actually flower and fruit as well under certain appropriate condition. For flowering and fruiting potato need certain environmental condition like cooler temperature and longer photoperiod.

Brief Intro:

Ø  Fruit type of potato is Berry.

Ø  Mode of pollination is self-pollinated.

Ø  Dr. S. Ramanujan (1940), the first Director of CPRI (Shimla) conceived the TPS (True Potato Seed) technique in India.

Ø  As the cost of production in potato accounted 40-70% for seed material (tuber pieces) only and a huge wastage of food material as seed along with non-availability of quality seed, continuously pushing to draw attention to TPS. For crop improvement program it is no doubt a useful tool.

Ø  China is leading country in TPS technology.

Objective of TPS:

ü  Development of superior parental line which is profuse bloomer and well berry setter in hills as well as in plains.

ü  Reduction of wastage of potato as seed material.

ü  The female parent should be male sterile and the male parent should produce abundant pollen.

ü  Seedling should show high vigour and must be tolerant to transplanting shock.

ü  Seedling should be high yielder and must be uniform in nature.

Advantages of TPS:

• Reduction in production cost. Cost of TPS is much less than potato seed tuber.
• Elimination of seed tuber transmitted diseases like potato Scab, Black Scurf, Virus and pest like Tuber Moth. Through seed the chance of transmission of disease is much more less. Only Potato Virus T (PVT) & Spindle Tuber Virus are known in TPS.
• Quality planting material can be served.
• In TPS wastage of food material is nil.
• Transportation cost is much lesser. About 100g seed is require for planting 1ha of potato.
• Cost for storing seed tuber is nil.

What are the procedures involving in production of TPS?

Under longer photoperiod and moderate temperature potato flowers profusely. After successful pollination potato produces small green tomato like fruit, called Berry. It means varietal improvement through hybridization is possible in potato. Field trials proved that hybrids are superior to open-pollinated or self-pollinated offsprings.

Flowering & fruiting of Potato

Potato flowering:

Being a temperate crop, potato needs cool temperature along with longer photoperiod. In hills generally potatoes are grown for flower during summer months where moderate temperature and longer photoperiod is ample. But in plains also flowering of potato is possible. In winter months, plains have cooler temperature with shorter photoperiod. So, flowering in plain is possible only through artificial lights to compensate the day lengths. It’s been observed that in North-Eastern Plains additional 5 hr of artificial lightning with 150-250 watts sodium lamps gave best result.

Planting of parental Lines:

For better management in commercial TPS production parental lines are planted in staggered way with a ratio of 4:1 (Female:Male). Generally male lines are planted about one week earlier to the planting of female lines.

Pollination and Hybridization.

Being an autogamous crop self-pollination is rule in potato. But along with self-pollination considerable amount of cross pollination also occurs in potato through insects. All these seeds are Open-Pollinated as only female parents are genuinely known to the breeder. Besides, hybrids are also possible under manual controlled pollination intended by a breeder.

Berry maturation, harvesting and TPS extraction:

About 7-8 weeks after pollination berry maturation becomes completed and becomes ready for harvesting. Before harvesting berry must be ripen enough in the mother plant. Even after harvesting green berries are allowed to ripen further in room temperature for a few days for the smooth extraction of seeds.

For small production of TPS manual extraction of seeds from the berry is feasible. But for commercial scale a reverse screw juice extractor was found to be effective. Seeds are separated from the pulpy tissues of berries followed by repeated washing in water. For the digestion of the adhered mucilage on seed surface 10% of HCL treatment helps to hasten the process. After proper washing and cleaning seeds are treated with 0.5% Sodium Hypochlorite to disinfect the seeds. Treated seeds are then dried in room temperature and subsequently under sun (for half an hour) to 4-5% of seed moisture. This ensures viability of seeds for longer time and helps in breaking dormancy. After drying seeds are stored in moisture proof container with 4-5% moisture level and 4⁰C temperature for long term storage.

TPS dormancy:

The seeds extracted from the shows dormancy of about 4-6 months depending on the progenies. The method of breaking dormancy varies with the utility of the seeds.

For immediate sowing, seeds are treated with 1500 ppm solution of Gibberelic Acid (GA). For late sowing seeds can be stored with 4-5% of moisture level and 30⁰C. It is very important to ensure the moisture level of seed should remain within 4-5% before exposing them into 30⁰C, else seed viability will be lost. It is advised to germinate the seeds in incubators before field sowing to ensure the maximised germination.

Growing TPS:

Planting of TPS varied according to the utilisation. Direct sowing in the field, transplanting the TPS seedlings and planting seedling tubers are followed mainly. Direct sowing is of least choice as newly borne succulent seedlings are more susceptible to disease and pests, abiotic stress, weed problems and inconsistent germination.

A.   Potato production through transplanting seedlings.

Like other vegetable crops, nursery raising of seedlings are also applicable in TPS Potato. The healthy seedlings, after proper nursery raising, are transplanted to main field. This method is cost effective as only 125g of TPS and about 75m² area is enough to grow seedlings for one hectare potato. This method is mainly advised in the area with mild temperature and evenly distributed rainfall or regular irrigation facility is available.

Nursery raising:

Nursery bed preparation are as like as in other solanaceous crops. Organic matter plays a good role on production of healthy seedlings.

·         Trench method (1m wide) or encompassing with locally available materials like bricks, stone tiles etc. is required to prevent washing away of the substrate/media during rain or irrigation.

·         Water stagnation must be avoided.

·         Proper plant protection measures must be taken as and when required.

In an about 15 days plants attain 8-10 cm height and bears 4-5 leaves. If needed after 15 days at 2 days interval 0.1% urea spraying helps to reach the stage. This stage is perfect for transplanting seedlings in main field.

Seed sowing:

·         The bed must be irrigated properly one day before planting seedlings.

·         Furrows on prepared bed is beneficial.

·         Row to Row spacing: 5cm, sowing depth 0.5cm, 100 seeds per one meter row.

·         Seed treatment with fungicide like Mancozeb is advised.

·         It is important to keep the bed moist during first 15 days of sowing for enhanced germination.

·         Seedling emergence occurs in about one week of sowing.

·         Under warmer climate (>25⁰C) shade is required.

Land Preparation, transplanting and intercultural operation:

For land preparation, transplanting and other intercultural operation standard potato production technique is followed. Importance must be given on proper irrigation specially during first 15 days of transplanting. 3 numbers of earthing-up and proper weed control is very much important. Irrigation must be given frequently upto the establishment of the seedlings but no irrigation should be given after 75-80 days after transplanting. Dehaulming is necessary if seed tuber is going to be used in next season.

Plant protection:

Though, TPS are more resistant to the diseases and pests, being succulent at seedling stage, TPS seedlings are more vulnerable to soil-borne diseases like Rhizontonia, Pythium etc. and aphids (carrier of viruses in potato). Proper protection measures are needed to be taken from the transplanting to the harvesting.

Dehaulming:

Dehaulming is one of the important operation in production of Potato through TPS either through nursery raised seedling or through tuberlets. Dehaulming is done at 90 days after seed sowing or as recommended according to the region. This process includes the cutting of green viney shoots above the ground. This reduces virus infection to the seedling tuber as aphids prefer lush green foliage to seedlings. Aphids are the vector of those viruses. Seedling tubers are harvested after 15 days of dehaulming.

B.   Potato production through seedling tubers:

Seedling tubers are generally produced from direct seeding in the main field or from the transplanted seedlings raised in nursery. Seedling tubers can be planted directly in the main field or can be raised in secondary nursery. The raising of TPS seedlings in primary nursery are same as transplanting seedlings.

After transplanting in main field the TPS first generation plant produces tuberlets which are stored for 4-5 months in cold storage like seed tuber pieces. After that the seed tuber or tuberlets are planted in next season in main field with standard potato growing technique and the final produce, the food potato obtained. Different grades of seedling tubers are planted with size specific inter & intra row spacing ensuring the uniformity.

Size grade (gm)	Planting spacing (cm)
	Inter row	Intra row
20-40	45-50	20
10-20	45-50	15
5-10	45-50	10

Spacing according to the tuber size.

Drawbacks of TPS:

1.    TPS takes comparatively more time than, vegetative seed tuber crops.

2.    Vulnerable to biotic and abiotic stress during initial stages (post germination seedling stage)

3.    Heterogeneity in morphological and tuber characters.