Organic manure and soil are the main components mixed in 1:1 ratio (v/v) for preparing the nursery substrate to produce TPS derived seedlings The organic manure may consist well-decomposed animal dung, compost or gobar gas slurry whichever is available. The soil from one feet from top may be used in the nursery substrate in areas consisting soil borne pathogens such as Rhizoctonia, Pythium, Ralstonia solanacearum etc causing damage to young seedlings.
The width of nursery beds is
kept one meter to carry out easily the manual operations such as weeding,
hoeing, earthing up etc. and the length may be kept as per requirement. In the
area marked for nursery beds, a trench is excavated to remove 4-5 inches of
topsoil and is filled with the prepared substrate mixture eventually raising the
level to about 3-4 inches above the ground level. Fertilizers @ 7.5 g Nitrogen,
8.0 g Phosphorus and 10.0 g Potash is added per square meter to above substrate
and mixed properly. Seedbeds are watered thoroughly with watering can or micro
sprinklers two days prior to TPS sowing.
TPS is treated with 0.01% Benzemidazole or any other systemic fungicides before sowing. Dry powder of the pesticide in smaller quantity may be added to the seeds and rubbed to form a fine coating on the seed surface. To produce seedlings for transplanting the TPS may be sown either in the rows or by broadcasting on the surface of prepared beds. The line sowing is preferred because i) seeds are placed at a uniform depth giving uniform seedling emergence ii) weeding and other cultural practices are performed easily. For quick and better germination/emergence true seeds are sown at a depth of 0.5 cm. The seeds are covered with a thin layer of pure farmyard manure (FYM) before watering the beds. Beds are kept moist by watering twice a day until the maximum seed germination is achieved. Later on watering the seedbeds once a day is sufficient.
Production of seedlings for transplanting: 0.5 cm deep furrows are marked 8-10 cm apart in the prepared nursery beds with moisture at the field capacity level. Seeds are dibbled uniformly in the furrows and these are covered with the same substrate mixture followed by a thin layer of FYM on top of this. Beds are watered with a micro sprinkler to avoid compaction and washing away of the substrate with run off water. Seedlings are ready for transplanting after 20-25 days of sowing. For broadcasting TPS is soaked for 24 hours in water and then kept at a cool place after mixing with sieved FYM and soil (1:2 ratio) for next 4-5 days to a stage when radical starts coming out. The pre-germinated seeds are evenly spread on the nursery bed @ 2 g/m2. The seeds are thinly covered with FYM powder and beds are immediately watered with sprinkler or watering can. The beds are kept moist until maximum germination is achieved. After 10 days the beds may be watered as and when required. After one week of seedling emergence 0.1 % solution of urea (1g urea in 1 litre of water) is sprayed at 2-3 days interval till transplanting. Thus the seedlings attain transplantable stage (4-5 leaf or 10-12 cm height of seedlings) after 25-30 days. The seedlings must be transplanted before stolon initiation to avoid yield losses. Only 150 g TPS and a nursery area of 75 sq. m is required to produce seedlings for transplanting a hectare area.
Production of seedling tubers: In areas where winter is harsh with short crop duration, the use of first generation seedling tubers, derived from TPS is advocated. Only 50 g TPS is required for sowing 350 sq m nursery area to produce enough seedling tubers for planting a hectare of commercial crop in the succeeding crop season. Seedling tubers also need cold store facilities for their storage like conventional seed tubers before planting in the following crop season. However, the space required for seedling tubers is considerably less than needed for seed tubers of a variety. The operations for preparing nursery beds and TPS sowing are the same as that for raising seedlings for transplanting. But the sowing of TPS for producing seedling tubers is done at 25 x 4 cm and two seeds are sown per hole. After germination thinning is done to maintain 100 seedlings per sq. m and one seedling/hole. The hilling is done by putting half the soils of inter row space on either side of the seedlings in a row covering lowermost 3 to 4 nodes. Haulms are removed at 90 days after TPS sowing and harvested one week later. The produce is graded and treated with 3% boric acid solution in water either as dip or spray to disinfest the pathogens on tuber surface before sending it to the cold store. On an average 400-500 plantable (2-40 g) seedling tubers can be obtained from an sq. m of nursery bed.
In some areas where duration of winter is comparatively longer, two successive crops of seedling tubers can be taken within one season. The second crop of seedling tubers in spring can be taken in the same beds from second week of January to the second week of April in Indo-Gangetic plains. For second crop no P and K fertilizers are added as basal doses. However, 75 kg/ha of nitrogen is applied at earthing up in two split doses and prophylactic sprays are given as required. The haulms are cut at 90 days from sowing of TPS and harvesting is done 10 days later. The yield of second crop is 50% lower than the normal seedling tuber crop with regard to size of seedling tubers but the number is almost same. Performance of these seedling tubers as commercial crop is similar to the seedling tubers produced under normal season.
In North-Eastern hilly areas
where crop is grown under rain fed conditions seedling are transplanted at
closer spacing of 10 x 10 cm on one meter wide raised beds following the normal
manurial and cultural practices recommended for the region. Experiments
conducted at CPRS Shillong reveal that 4-5 kg seedling tubers can be obtained
from a square meter area by transplanting the seedlings at closer spacing.
The same procedure of field
preparation as adopted for traditional potato cultivation through seed tubers is
also used for growing the potato crop from TPS derived planting material
(seedling transplants and G0 seedling tubers). The care needs to be taken that
the soil has moisture at field capacity at the time of planting and there are
not much clods in the field for transplanting seedlings.