Managing physiological disorders of tomato (Lycopersicon esculentum) in India
Authors: Kavita1 and Sangeeta Kumari2
1 Assistant Professor cum Jr. Scientist (Plant Physiology), FBS&H, Rajendra Agricultural University, Pusa, Samastipur- 848125 (Bihar), India
2Assistant Professor (Horticulture), Agricultural Research Institute, Lohiya Nagar, Patna under Bihar Agricultural University, Sabour, Bhagalpur (Bihar), India

Tomato is the most popular vegetable in the home garden. Though widely grown, tomatoes are subject to a number of diseases and physiological disorders. Diseases are biotic in origin whereas physiological disorders are abnormalities in fruit colour or appearance that are abiotic in origin. These abnormalities are often confused with damage from pathogens or insects (biotic damage). Physiological disorders are also different from deficiencies of a single nutrient, and physical, chemical or herbicide injury. Causes of physiological disorders include genetic susceptibility, environmental factors, watering practices, nutrition, and cultural practices such as pruning and training. The common physiological disorders of tomatoes in India, their causes and control measures are described.

1. Blossom - end rot:
This is the most common and destructive disorder.

Symptoms: Brown, water-soaked discolouration appears at the blossom end of the fruit where senescent petals are attached while the fruit is still green. The spots enlarge and darken rapidly and the affected portions of the fruit become sunken, leathery and dark coloured.

Causative factors:
i) Sudden change in the rate of transpiration especially in moisture stress condition.
ii) Continuously high evapotranspiration regime and a large leaf area.
iii) Increasing level of nitrogen content in the fruits.
iv) Fall in the level of Calcium content in the fruit.

Control measures:
• This disorder is decreased by increasing the frequency of irrigation.
• Increase in the level of phosphate decline the incidence of this disorder.
• Liming decreases the incidence.

2. Fruit cracking: Two types of fruit cracking are seen:

Symptoms : Radial cracking, where surface of the mostly full ripe fruits cracks radially from the stem end of the fruit and concentric cracking where surface of mostly mature green fruits cracks concentrically around the shoulder of the fruit. Radial cracking is more common and causes greater loss than concentric cracking.

Causative factors:

i) Irrigation or rainfall after long dry spell.
ii) Exposure of fruits to sun due to pruning and staking.
iii) Boron deficiency.
iv) Genetic factor which is reportedly inherited polygenically.

Control measures:
• Irrigation at regular intervals.
• Pruning and staking during summer season should be avoided.
• Picking of fruits before fully ripe stage which reduces radial cracking.
• Spraying the tomato seedlings before transplanting with 0.3 - 0.4% borax solution and repeating the sprays at the time of fruiting, 15 days after second spray and at first ripening stage.
• Growing resistant varieties like 'Punjab Chhuhara', 'Pusa Ruby', 'Arka Saurabh', 'Sioux', 'Roma' etc.

3. Puffiness:

Symptoms: Outer wall of the grown up fruits continues to develop normally but growth of the remaining internal tissues (placenta, mesocarp) is retarded resulting in partially filled fruit which is light in weight and lack in firmness. Cross section of affected fruit shows emptiness or pockets.

Causative factors:
Any factor that affects fruit set, including inadequate pollination, fertilization, or seed development

Control measures:
In boron deficient soil condition, boron should be applied by spraying 0.3-0.4 % borax solution at initial plant growth, fruiting and fruit development stages.

4. Cat face:

Distortion of the blossom end of the fruit gives rise to various ridges, furrows and indentation in a localized area of the fruit. Usually such fruits are unmarketable. The disorder is named 'Cat face' due to these ridges and indentations.

Causative factors:
i) Abnormal growing conditions during formation of blossoms cause death of the cells of the blossom end of the ovary which turn dark to form a leathery blotch at the end of the fruit. Unlike blossom- end rot, the patch does not progress and thus gives rise a localized affected area.
ii) Cool or cold temperatures that occur about 3 weeks before bloom can increase the amount of catfacing.
iii) In indeterminate varieties, catfacing is thought to be related to reduction in auxins in the plant from removing the growing points.
iv) Drifts of herbicides such as 2,4-D can cause fruit to catface.
v) Heavy thrips feeding on young fruit can cause a type of catfacing, also fruit on plants that are mildly affected by Tomato Little Leaf are severely cat faced.

Control measures:
There is not much that can be done for control. Varieties should be selected that historically have had little problem with catfacing. Try to prevent spray drift from undesirable chemicals and in the case of little leaf, prevent soils from becoming waterlogged.

5. Unfruitfulness:

Temperature, particularly night temperature has profound effect on fruit setting in tomato. High day temperature (above 32 °C) and high night temperature (above 20 °C) is not congenial to fruit set. On the other hand, fruits normally fail to set at or below 13 °'C. Both high and low temperature adversely affects fruit set mainly by reducing pollen viability and pollen germination on stigma. For this reason, low fruit set is a problem during summer cultivation in eastern India, especially in West Bengal where temperature remains above the critical limit and during winter cultivation in northern India where temperature falls far below the critical level in winter.

Control measures:
• Growing high temperature tolerant varieties or line like HS102, Punjab Kesri, Punjab Chhuhara, Hot Set etc.
• Growing low temperature tolerant varieties like ‘Pusa Sheetal’, ‘Cold Set’, ‘Ostenkinskiz’ etc.
• Application of growth substances like parachlorophenoxy acetic acid (PCPA) 50 ppm at full bloom stage.

6. Low temperature injury:

Tomato is very sensitive to frost. As the maturing fruits are exposed to near freezing temperature, accumulation of sugar in the fruit juice lowers the freezing point slightly. As a result, the fruits become soft, water-soaked and dull coloured. Low temperature injured plants become darken, desiccated and wither.

7. Delayed ripening and colour development:

In the process of ripening fruits, the green chlorophyll pigment is delayed and yellow-orange carotenoid and the lycopene pigments are synthesized. Rate of ripening and colour development of red colour is suppressed above 30°C. Similarly, at temperature below 10°C, ripening and colour development get hindered. For this reason, delayed ripening and colour development is a major problem during both high and low temperature condition at the time of fruit ripening.
Control measures: In spring-summer and early autumn-winter growing condition, the plants should be sprayed with 250 ppm ethrel at turning stage of the fruits which hastens ripening and gives early yield.

8. Gold Fleck:

Around the calyx and fruit shoulder, small irregular shaped green spots develop at random on the surface of immature fruit, which become gold in color as fruit ripens. These tiny yellow spots are called gold flecks. These gold flecks appear due to deposition of calcium oxalate. With high incidence, fruits become unattractive and their shelf-life also gets reduced.

Causative factors:
i) Higher supply of phosphatic fertilizers.
ii) Higher supply of calcium fertilizers.
iii) Increased magnesium concentration in the fruits.

Control measures:
Summer shading lowers the incidence of this disorder.

9. Pithy Stem:

In this disorder, large air spaces are formed in the pith accompanied by an increase in abscisic acid levels in the leaves. Water uptake is prevented due to this disorder. This disorder has been ascribed to both under and over irrigation.

10. Crease Stem.

In this disorder, pronounced grooves or creases develop on the opposite side of the stem. In severe cases, the creases become deeper and eventually a slit right through the stem is visible. This disorder appears under high nitrogen and water supply condition.

11. Oedema or Dropsy:

Symptom of this disorder is formation of blisters or pustules on the lower surface of the leaves, petioles and peduncles. With the progress of this malady, twisting and distortion of the leaves leading to necrosis is caused. This disorder is caused when the plants take up excess water than it can loss through transpiration. For this reason, over watering may initiate this disorder.

12. Silvering:

This disorder may affect stems, leaves and even flowers. In the stem silvering, grey-green stripes of varying number and width appears. Discrete grey-green patches of varying sizes also appear on the leaves. In some plants, silvering affects primary meristem where the whole shoot becomes grey-green in colour which is called ‘head silvering’. This disorder may be caused due to exposure of plants to temperature below 21°C for sometimes. This disorder sometimes occurs in single stem trained plants.

About Author / Additional Info:
Author is an Assistant Professor (Plant Physiology) at Rajendra Agricultural University, Pusa, Samastipur, Bihar (India). Currently engaged in teaching plant physiology courses to undergraduate and postgraduate students. Her area of research is stress physiology of crops, especially maize and rice.