Breaking Dormancy in Potato Tuber
Binomial name of potato is Solanum tuberosum L. and is a root crop. About 100 varieties of potato used as food, whether mashed, baked or in chips form and as food additives such as Starch. Potato (Solanum tuberosum L.) is the staple food of many countries such as in Ireland. It is native to South America and introduced in Europe by Spanish people.
Potato is a very nutritious crop containing vitamins, potassium, copper, manganese, phosphorus and fiber. It also contains phyto-nutrients that act as antioxidant. It has the potential to decrease blood pressure. An important nutrient vitamin B6 builds cells of body and increase the activity of nervous system. Vitamin B6 also protects cardiovascular system and helps to prevent cancer.
If potato is used with care it acts as friend of health but in case green, damaged potato is used it may result in stomach pain, vomiting, diarrhea, nausea etc. Damaged or green potatoes contain some poisons material which may cause death. However, a small care can overcome this problem.
Its production depends upon many environmental conditions such as humidity, irrigation, temperature, light moisture content of tuber, moisture content of environment etc. But its production is seemed to be very good in temperate climate where temperature is low with low precipitation. Its year-round production is not possible in most of the countries. For year-round consumption, Solanum tuberosum L. is stored in dormant conditions.
As it is a seasonal crop so, it must be stored for next year consumption. However, potatoes produce sprouts during long-term storage for industrial processing and fresh market (Saraiva et al., 2004). Sprouting affects the quality loss of tuber, softening, shrinkage, weight loss and market price of potatoes, which results in a significant economic loss during storage (Friedman and McDonald, 1997). To prevent sprouting different sprouting inhibitors are used such as chlorpropham, maleic hydrazide and carvone. CIPC sprout inhibitor is the most effective as well as registered in many countries (Saraiva and Rodrigues, 2011). However different ecological unsafe synthetics are also used to inhibit sprouting.
For propagation purpose, potato should not be in dormant condition. Dormancy is a physiological condition in which plants respond to stresses by entering into a state of growth suspension (Campbell et al., 2008). During storage, it starts sprout if it breaks its dormant condition. However, for propagation its purpose is to break dormancy. Different methods are used for this purpose such as use of hormones, use of chemicals, alteration of temperature thiourea, carbon disulphide etc.
For heat treatment, tubers are placed at 19-224 degree without light. This is not recommended for breeding purpose.
Use of electric current is one of them. For this purpose, two tubers of Agria and Famosa cultivars are taken. Age after harvesting was 20 days. Electric current is applied in it by inserting needles on opposite side of tubers. Needles connected to electric stimulator to get voltage. Current is applied in two ways with different potential difference:
- i) Continuously for 50 seconds, and
- ii) With a 60 Hz repetition for 50 seconds.
After passing current, these tubers are placed in incubator at 20 degree with 60% relative humidity. In agria cultivar after five days sprouting is stared at 50 voltages while in Famosa cultivar, sprouting is started with potential of 100 voltages. At potential of 10 volts no sprouting is initiated.
In this method, electric current is used instead of chemicals. Mechanism of sprouting is not certain. Current may alter the permeability of membrane or may stimulate Gibberellic acid to break dormancy and start sprout.
As discussed above, different methods used to break dormancy. Use of gibberellic acid is also common at different areas of the world. For this purpose, an experiment was conducted. Ten tubers of 10-day age after harvest were used. They are treated with gibberellic acid for 10 to 20 minutes in 5 to 9 ppm. Criteria for sprout are that a tuber sprout length must be minimum 2mm. After two weeks 80% dormancy was broken.
Thiourea is a safe method but not common. Tubers are soaked in 1% solution for about an hour. After treating with thiourea store them with at about 25 degree.
Different methods for dormancy breakage are used and every method has its own importance. Use of gibberellic acid is used as common but Pakistani farmer use methods violently depend upon their source of income and availability of source. Evenly Sometime farmer don’t use any method but place in sunlight for two to three days.
This article is jointly authored by Muhammad Umar, Institute of Horticulture Sciences, University of Agriculture, Faisalabad, and Umer Ijaz, Imran Khan, Zain ul Abdin, Maqsood ul Hussain, Department of Agronomy, University of Agriculture, Faisalabad.