Tuberization is a complex biological phenomenon of formation of tuber which is affected by genetic, environmental and nutritional factors. This presentation is about tuberization of potato. Those who go through this, will definitely know about various aspects regarding tuberization of potato.

1. TUBERIZATION IN POTATO
Komal Rijal
Agriculture and Forestry University, CNRM Pakhribas

2. DEFINITION
• Complex biological phenomenon of formation of tuber which is
affected by genetic, environmental and nutritional factors

3. TUBER
• Thickened underground stem serving as a food reserve and bearing
buds from which new plant arise.
• Tuber is stem because it has nodes and internodes which is a
distinguishing character to be stem.
• Tuber formation on other axillary nodes on the stem or even flowers
is also possible
1. When highly inducing conditions are available
2. When the plant is diseased or injured
3. When translocation of assimilates to tuber has been prevented.

5. Swelling of tuber
• Occurs when stolons stops to elongate and the cells in the pith nd
cortex enlarge and divide transversely.
• Later the cells in the perimedullary region enlarge and divide
randomly.
Transverse: At right angles to the long axis of the body

8. Factors affecting tuberization
• Genetic
• Photoperiod
• Light intensity
• Temperature
• Gibberlic acid
• Nitrogen

9. Photoperiod
• Interval in 24 hours period during which a plant is exposed to light
• Potato is a short day plant.
1. Short day photo period<8-10 hours
2. Long day photo period > 16 hours
• With photo periodic responses it is actually the length of the dark period
than light period

11. Long day photoperiod
• Significantly delays and reduce tuberization, promote profuse haulm
growth resulting in
1. More branching
2. Increased plant height
3. More flowering
4. Many secondary stems
5. Delayed plant senescence
• In LD condition, stolons move upward and emerge out from the soil
to form a new shoot.

12. Short day photoperiod
• Promote tuberization
• Stolons grow underground until tip of stolon swells to form tuber
• Promotes higher rate of photosynthesis per unit leaf dry weight
thereby more starch accumulation in leaf during day.
• Assimilates export from leaves(source) to storage organs(sink) is also
higher.

14. Temperature
• Optimum temperature: 15-20 °c
• At 20-25°C, profuse vegetative growth occurs.
• Above 25°c tuberization stops
1. Higher temperature >25°c
2. Lower temperature < 20°c

15. High temperature
• Inhibits tuberization
• Inhibitory for both long and short photoperiods.
• Inhibitory effect higher for long photoperiods at higher temperature
because
1. Assimilates are used for vegetative growth thereby decreased
amount going to tubers
• High soil temperature: stolons move upward, when come in contact
with cooler air in surface, tuberization occurs.
• Also causes secondary growth of tuber forming chain tubers.

17. Low temperature
• Promote tuberization
• Produces Abscisic Acid and CCC ( Chloro Choline Chloride) which
reduces the growth of haulms.

18. Nitrogen level
• C:N ratio important for tuberization
• High level of carbohydrates in the form of sugar and starch favour
tuberization
• High nitrogen promotes shoot growth
1. As available carbohydrates is used for shoot growth, decreased
amount available for tuber formation

19. Light intensity
• Higher light intensity: promotes tuberization
1. Higher sucrose levels due to higher photosynthetic rate
2. At higher light intensity and low temperature, 80% of the plant dry
matter diverted towards tuber.
• Low light intensity – reduces tuberization because of shading effect
• Results into
1. Delayed tuber initiation
2. Taller plants
3. Thinner stems
4. Small leaves

20. Gibberlic acid
• Inhibits tuberization
• Has similar effects as that of
1. High temperature
2. Long day condition
3. Higher nitrogen level

21. Genetic factor
• mRNA of BEL5 transcription factor has been found to move from
pholem to stolon tip to induce tuberization.
• Micro RNA miR172 is also found to induce tuberization.

22. Conclusion
• All factors are directly related with amount of GA in plants.
1. Low GA- induces tuberization
2. High GA- suppress tuberization
• Tuber formation at low GA and stolon formation at high GA
• High sucrose reduces endogeneous GA
• High nitrogen increases endogeneous GA