TOMATO, scientific name Lycopersicon esculentum Mill. (Family: Solanaceae) is one of the most important vegetables in many regions of the world.
It is used in almost all food preparations in the tropics. it is grown under rainfed conditions and irrigation.
Origin of Tomato
It’s native to central and south America, most likely Peru and Ecuador from where it spread to Mexico.
It was brought to Europe from Mexico by the Spanish in 1523. From Europe, it spread to other parts of the world, and it’s now wildly grown throughout the warm temperate and tropical regions of the world.
The Ecology
Tomato plant grows well in the tropics, especially in the drier parts. It can grow in both hot and wet weather as long as it’s on good soils, however, it thrives well in wet weather with low sunshine and high temperatures.
The plants are sensitive to frost and will not normally set fruits when night temperatures fall below 18°C.
Tomato can be grown at sea level in the tropics but usually, do better at higher altitudes. It can be grown in a variety of soils but a light, free-draining, fertile loam soil with a pH of 5-7 is the best for the plant.
Flowering is not affected by photoperiod (I.e. it is day neutral). In temperate areas, tomato is often grown in glasshouses.
Botany of Tomato
It is an annual herbaceous plant with a weak stem that may be erect, semi-erect, or trailing.
It has many branches and is coarsely hairy with a characteristic strong odor.
The seedling produces a tap root, but this is usually damaged in transplanting and an extensive copiously branched, fibrous root system develops in its place.
Adventitious roots arise from the base of the stem and it bears numerous alternate leaves.
The flowers are borne in clusters on the main axis and in lateral branches are carried on fairly short pedicels.
In some varieties, especially temperate ones, self-pollination is common whereas most tropical varieties are cross-pollinated.
The fruit at maturity is a reddish or yellowish berry with smooth skin, varying in shape and size with varying thickness of pericarp.
Tomato cultivars differ in a great deal of size, shape, and color. The red coloration of the fruit is due to the presence of two pigments, carotene and lycopersicin (lycopene) occurring in different concentrations.
The seed is flat, kidney-shaped, light brown and cont,ains a curved embryo lying in the endosperm.
Cultural Practices of Tomato
Tomato seeds are first down in the nursery and transplanted later into the field. The crop can be grown throughout the year provided it is irrigated.
The best crop is obtained in the dry season under irrigation. Seedlings are raised in beds at the beginning of the rain.
In an area where there’s the season when rain falls regularly, the crop can be planted twice a year.
In Nigeria for example, the plant is transplanted at 3-4 weeks in April ( for the first session) and in the second session, it’s done in August. Even for the third session, the crop is transplanted from late September to October.
A a spacing of 60cm between plants on 75cm ridges is used for non-staked tomatoes and 30x60cm for the staked crop.
Mulching may be beneficial as it can conserve moisture and control weeds.
Weeding should be done twice in the third and sixth weeks after planting. Avoid weeding once fruiting has commenced.
Metribuzin at the rate of 1.5kg/a.I/ha can be applied before planting. Recommended fertilizer application is 200kg/ha of NPK, split at 0 and 6 weeks after planting.
Harvesting of Tomato
Tomato matures in two to three months after planting. As the fruits do not mature at the same time, harvesting is spread over a 3-4 week period.
The stage of maturity at which tomatoes are picked depends on the purpose for which they are grown. For distant marketers, tomatoes can be harvested when fully mature but still green.
Local marketers, they are picked when pink or firm ripe. Containers for packing tomatoes should be rigid and have adequate ventilation.
In recent years, a remarkable accomplishment has been the development of farms with special characteristics that permit them to be harvested mechanically.
Yield Expectations
Farmers can harvest about six tonnes/ha of fresh tomatoes. Under improved management, yields can be up to 30tonnes/ha, especially under irrigation.
Storage
Tomato contains 90% water and so it readily deteriorates in quality. It can be cold stored at 10-15°C. It can be processed and tinned. This is perhaps the best method of preserving tomatoes.
Chemical composition
Ripe fruits contain approximately
- 94% water
- 1% protein
- 0.1% fat
- 4.3% carbohydrate
- 0.6% fiber and
- vitamins
The color of the mature fruit is due to lycopene and carotene but the former is absent in yellowish fruits.
Uses of Tomato
- Often eaten fresh as a salad.
- Processed in the canning industry into pastes or purees which are used for cooking in soups, stews, ketchup, sauces, and other products.
- The seeds contain 24% oil and this semi-drying oil can be extracted and used as a salad oil, and in the manufacture of margarine and soap.
- The residual press cake is used for stock feed and fertilizers.
Diseases of the Tomato Plant
The diseases can be classified into wilts and leaf diseases.
(A) Wilts include:
1. Bacterial wilt is caused by Pseudomonas solanacearum.
This is one of the most serious diseases of tomatoes in the tropics particularly if waterlogging occurs.
It produces a rapid wilting without yellowing, followed by death. Little resistance has been found.
2. Fusarium wilt caused by Fusarium bulbigenum & Fusarium lycopersici. The disease causes wilt accompanied by yellowing of the leaves.
3. Sclerotium wilt caused by Sclerotium Rossii. It causes rapid wilt. The plant is attacked at ground level and white leathery mycelia encircle the stem, followed by the production of sclerotia.
(B) Common leaf diseases include:
1. Leaf spot caused by the fungus Septoria lycopersici.
The disease is manifested by the appearance of small brown spots, first on the lower leaves and then on all the leaves.
The disease is most prevalent in wet weather. Control is by weekly sprays with fungicides, e.g. Bordeaux mixture or Dithane M 45.
2. Leaf mold caused by the fungus Cladosporium fulvum. It occurs in humid weather.
There is mouldiness on the underside of the leaves and the leaves later shrivel and turn brown.
Control is by spraying with Bordeaux mixture.
Other diseases include those that affect the fruit e.g blossom-end rot.
Blossom-end rot occurs when tomato plants have been growing under dry conditions.
The blossom end of the fruit rots and turns black. The best control is not to let the plants experience drought.
Insects Pests affecting Tomato
Various insect pests eat up vegetative parts of the plant but they are not of economic importance.
- Fruit Worm
An insect pest that does a lot of d damage is the fruit worm. The fruit worn is the larva of the American bollworm (Heliothis spp.)
It bores into the fruit and causes much damage. It also paves the way for fungal and bacterial infections resulting in fruit rot.
Control is by spraying with insecticides such as detox or Didigam. Aphids can be troublesome, especially in the dry season of irrigated crops. They can be controlled with malathion.
- Root-knot nematodes
The root-knot nematode (Meloidogyne spp.) causes galls to develop on the roots. This results in retarded growth and decreased yields.
Three methods of control are common:
i. Use of resistant varieties.
ii. Crop rotation with crops that are not susceptible, e.g. Okra, maze.
iii. Fumigation of the soil before planting using a nematode killer, e.g. Nemagon 20.
