Major physiological disorders of potato and it’s control measures

Introduction:

Potato is the fourth major crop after rice, wheat and maize in the world. It’s probable centre of origin is South America in the central Andean region. Potato is a temperate crop grown under subtropical conditions in Nepal. The potato is a crop which has always been the ‘poor man’s friend’. Potato being an economic crop with a good source of nutrients such as starch, vitamins especially C and B1 and minerals enters the kitchen of almost all people of our country. They contain 20.6 per cent carbohydrates, 2.1 per cent protein, 0.3 per cent fat, 1.1 per cent crude fibre and 0.9 per cent ash. They also contain a good amount of essential amino acids like leucine, tryptophane and isoleucine etc.

In the context of Nepal, potatoes are widely grown at below 100 m altitude in the south to as high as 4 000 m in the northern mountains. It is used as vegetables in the terai region and as the major staple food in some place of mid hill and high hills of Nepal. Although Nepal has a good potential of production of potato but every year farmers should bear a great loss in the yield due to many physiological disorder seen in the potato tuber. Unbalanced dose of fertilizer

The most destructive and destructive physiological disorders of potato and their management are described below:

1. Black heart:

It is seen in the internal part of the potato tubers. The affected tissue are hard and leathery. The tuber with this disorder have greyish black to black inside.

Cause: Develops as a result of oxygen shortage or an oversupply of CO2 which causes the tissue to die, especially if the oxygen shortage is accompanied by high temperatures.

• Black heart can also occur in the potato field if high temperatures follow excessive rain which causes an oxygen shortage in the soil.
• When harvested tubers are left on the land for a long time.
• When seed planted by hand lie in furrows for a long time before being covered by soil, especially when it is very hot.

Management: After harvesting do not leave tubers in the sun on trailers under tarpaulins

• Ensure sufficient ventilation during storage and transportation
• Avoid fields with poor drainage if rain is received in the after season
• Make sure that lifted tubers are picked up as soon as possible
• Cover seed tubers in furrows as soon as possible after planting
2. Hollow heart:

In this type of disorder even the potato is seen healthier from outside but there is the presence of cavities lengthwise or diagonal inside the tuber. This disorder make a cut fresh-market tubers unattractive and can also reduce repeat sales.

Cause: These brown core are developed when the tubers are exposed to the low temperature (<15 degree Celsius).

• Rapid growth and development of tubers followed by sudden rains or irrigation.
• Excessive use of nitrogen and water application increases the incidence of hollow heart.
• Wide plant spacing promotes bigger tubers and tends to favor hollow heart.


Management:

• Follow closer spacing.
• Avoid excessive application of fertilizers particularly nitrogen.
• Apply irrigation at short interval so that the soil temperature may not exceed 32 tuber development and mature.
3. Cracking:

It is an external noninfectious disorder of the potato tuber in which the tuber splits while growing. The split heals but leaves the figure in the tuber affecting the overall quality of the potato. It is seen more in wider plant spacing or if fewer tubers are set per hill.

Cause:

• Irregular water supply is often responsible for growth cracks. A heavy rain or irrigation followed by dry spell causes rapid increase in growth activity and water uptake.
• Chances of cracking increases when potato plants are abruptly growing conditions after a period of poor growth conditions.
• Deficiency of Boron also contributes to cracking.

Management:

• Proper soil moisture should be maintained during growing season especially during bulking stage when the plants are large and tubers are rapidly expanding.
• Borax @20kg/ha should be applied in the field to overcome the boron deficiency.
4. Brown spot:

It is characterized by numerous , numerous, irregular, dry reddish brown or rust coloured spots beneath the tuber skin, with few or no out ward signs. The spots can be anywhere but most commonly found inside the vascular ring and towards apical end. Spots consist of group of dead suberized cells that are free of fungi and bacteria. There is no external symptom but the tubers lose their value as table potatoes.

Causes:

• Unfavorable and adverse soil condition, with irregular irrigation are some reasons for this disorder.
• Storage of immature tubers at high temperature also have a higher incidence of brown spot.
• Deficiency of calcium.

Management:

• Application of adequate calcium fertilizers after planting.
• Adequate soil moisture should be maintained in the field and avoid high soil temperature. Tubers should be only harvested after full maturity.
• Proper scientific system of storage with all the necessary condition should be assured.
5. Greening:

It is most common disorder seen in the potato. It is due to the exposure of tubers to the bright sunlight or longer periods of low intensity of light. It results in the formation of green pigment just below the periderm of the tuber. These tuber contain a few glycoalkaloids like solanine and chaconine which are considered poisonous. Such potatoes taste bitter and may cause temporary digestive discomfort. Peeling off green skin with layer of the flesh removes most of the solanine content.

Causes:

• The main cause of greening in potato is due to exposure of tubers to sunlight and If harvested potatoes are stored in the home under low levels of light.
• Excessive application of fertilizers may also contribute to this disorder.
• Mechanical injury may also leads to solanine production which results in green color of the tuber.

Management:

• Intercultural operation such as earthing up should be done in the right time which prevent the exposure of tuber to the sunlight. Two earthing are sufficient to keep the potato tubers safe from the greening.
• Use packaging materials that provide sufficient protection against light transmission if potatoes are exposed to light for more than a few days. White paper transmits more light than brown paper.
6. Freezing injury:

It is characterized by discoloration of the tissue and affects vascular tissue of the potato. Exposure for short periods to temperatures around 2˚C – 0˚C can result in grey or reddish tissue. The tissue can also turn dark grey or black. If the tubers are frozen for about 4-5 hrs. they show no blotch or discoloration but on thawing the whole tuber becomes wet and soft and liquid oozes out of it.

Cause:

• This disorder occurs due to the exposure of tubers to freezing temperature during or after harvest. It takes place at potato tubers.

Management:

• Avoid cultivars that tend to bear shallow in regions with low temperatures at the end of the growing season.
• Avoid exposure of tubers to freezing temperature during storage or harvest.
• Adjust the date of sowing so that it does not coincide with low temperature.
• Lift potatoes before there is risk of frost or use frost tolerant varieties if available.
• Avoid storing field-frosted tubers or using them for seed purpose.
7. Loose skin:

The skin is totally or partially removed from the tubers leading to the underlying tuber tissue being exposed.

Cause:

• Excessive application of nitrogen (N) late in the season and wet soil may delay ripening and promote loose skin.

Management:

• Top-growth must be completely dead 14 to 21 days prior to harvesting to promote skin setting.
• Ensure that the harvester is properly set to prevent tuber damage.

Conclusion:

Among a number of factors are responsible for low productivity; disorders among them are most important ones. Plants that are growing in less than ideal conditions are prone to physiological disorders that appear in different forms in the tubers. So, effective and timely management practices of fertilization, irrigation should be adopted in the potato field for the control of these devasting disorders.

Writer : Babita Bhusal