TOMATO

BIOLOGY AND MORPHOLOGY

Tomato (Lycopersicum esculentum) come from the origin is a mountainous region in Andes (Peru, Ecuador and Chile). Domestication of tomato occurred in Mexico and the name tomato came from an Indian language in Mexico. From Mexico it was spread throughout the world. About 450 years ago, it was imported to Europe, where it was originally believed to be poisonous and it was not eaten.

Cultivated forms of tomato are herbaceous perennial plants. Tomato is a tender, warm-season vegetable crop with an optimum temperature for growth in the range of 21-23 °C. Both very low and very high temperatures may cause problems in fruit setting and malformation. Direct sunshine is also need. Shaded plants can also have problems in fruit setting, or it is delayed. The tomato plant is covered by glandular hairs that emit a strong aroma when broken. 

By growth type, we distinguish between continuous, determinate and semi-determinate varieties.  As for berries, we distinguish between spherical, flattened, elongated and angular ones. Berry size can be cocktail, cherry, medium and large. According to the type of cultivation, varieties are suitable for field, propagation, and both. The colour of the fruit can also be very varied: red, yellow, orange, pink, burgundy, black, green, white. 

The primary shoot of a young tomato plant produces 5 to 10 leaves, then produces a flower cluster. Each flower cluster is referred to as a 'hand'. In indeterminate cultivars, the shoot continues to grow upward and flower clusters appear to develop to the side of a main shoot or main stem. In greenhouses, main stems are sometimes allowed to grow indefinitely and can reach 3 to 6 m in length. In this training system, vegetative side shoots or suckers which form in leaf axils are removed. Although indeterminate plants appear to have a single main stem, this is actually not the case. The growth of the primary shoot ends with the formation of the first flower. Upward growth continues because the last leaf initiated before the flower cluster (which actually grows to occupy a position above the cluster) produces a side shoot.

Flowers and fruits:
One plant can bear several inflorescences (6-8 in field conditions) usually formed from four to ten flowers. Tomato flowers are relatively small and consist of a five-lobed corolla and calyx. The staminal cone represents a fusion of five anthers around the ovary, style and stigma. Pollen is released on the interior of the anther, and it ensures high level of self-pollination.

Pollination can be done either by air currents or by pollinating insects. If the temperatures during flowering are either too low or on the contrary too high, pollen is not able to germinate and flowers are not pollinated which results either in flower falling off or formation of small almost seedless puffy fruits. Such temperatures can also cause fruit malformations, so called catfaces, which are result of incomplete separation of cells during early stages of flower and fruit development.

From the botanical point of view, the fruit is classified as a berry. Inside it can have two to several locules (divisions of ovary). Wild-types (cherry tomatoes) have two locules, most commercial varieties have 4 - 6 locules and processing tomatoes have more locules. Colour of fruit at full maturity is usually bright red, but can also be bicolor (red and yellow streaks), yellow, orange, almost black, green or even white. Red colour is a result of two carotenoid pigments, lycopene and ß-carotene. The higher is lycopene content, the deeper red is the fruit. On the contrary if temperature is higher       lycopene synthesis slows, and the colour of fruit is orange. Final colour of fruit is given by the ratio between the colour of skin and that of flesh.

There are at least six different types of fruits: most common classic round tomatoes, smaller cherry or cocktail tomatoes, distinctive oval plum and baby plum tomatoes, larger beef tomatoes, and vine or truss tomatoes, which can have any of the above-mentioned shapes but are marketed still attached to the fruiting stem. Development of fruit to full ripening can take between 6-10 weeks. According to the time between transplanting and harvest, varieties are divided into three categories: early which need 50 -65 days, mid-season (70 - 80 days), and late cultivars (85 - 95 days). Ripening stages of tomato fruits (red) are described as immature, mature green, breaker, pink and red. Fresh marked tomatoes are often harvested at green maturity because thus they tolerate rough handling better than riper stages. Only vine tomatoes are harvested later and may be preferred by some consumers because of their better flavour. Tomato fruits contain approximately 95 % of water, the resting part is constituted from sugars, organic acids and other compounds giving the fruit characteristic flavour and texture. Processing cultivars have thicker walls and higher content of soluble solids. Fruits are important source of antioxidants. One of the most powerful, the carotenoid lycopene, has been shown to confer health benefits. It reduces the      risk of prostate cancer. The high content of vitamin C is also valuable, especially during winter. Fruits are used as vegetable. They are eaten either fresh as a snack or a part of salads or boiled as a part of sauces, soups, etc. Some varieties are especially bred for extra high carotenoid content and are used in industry.

Varieties:
From the genetical point of view, existing tomato varieties either are classic populations obtained by classic breeding or F1 hybrids which are obtained from special parental inbred lines by the crosspollination. In this case all plants coming from one crosspollination are genetically uniform. The advantage of F hybrids is in so called heterosis effect, it means that offspring of two inbred lines can have much higher yields and quality than either parental line. To achieve this effect for each generation of seeds parental lines have to be crosspollinated (it is not possible to further cultivate plants from seeds from F1 generation, because in F2 generation properties of plants would segregate). For this reason, the seeds of F1 hybrids are more expensive, but are preferred. Varieties and hybrids are also bred for resistance to some diseases and pests, and also resistance to fruit cracking and slow postharvest softening.

The steps in growing tomatoes can vary depending on the purpose of the crop and the growing equipment available.

During shady days temperature should be kept at minimum to prevent excessive elongation of plants.      Cultivation in greenhouses depends on the countries, and geographical area, in central Europe cultivation last (about 6 - 7 weeks). Hardening of transplants before planting into field is essential to prevent mechanical damage during replanting and damaging by sunshine and wind after replanting. Temperature should be lowered and watering is also reduced. In hotbeds glasses should be removed during day. Good transplant should be compact, with hard thick stem, and dark green leaves. These transplants are planted in the field at mid-May usually with first inflorescence appearing. Containerized transplants grow more rapidly after transplanting but their price is higher. Another possibility is direct sowing into field. This is mainly used for processing tomatoes. In this case seeds are sown during last decade of April. Sunny localities are preferable. Deep valleys and closed localities near water surfaces with high air humidity should be avoided. Tomatoes can successfully grow on many types of soil but silt or clay loam soils with high organic matter content are considered to be the most productive. Fresh manure should not be applied prior to tomato cultivation. Good soil drainage is essential. Optimal pH is 6.0 to 6.5. Field preparation procedures are very site- and machinery- dependent and must consider both all requirements of plants and cropping technology. 

Maintenance:

Irrigation and fertilization are also essential for good yield and quality because plants grow very quickly but overhead irrigation and high doses of nitrogen make plants vulnerable to foliar diseases. Excess of nitrogen or other elements can also induce calcium deficiency in fruits, so called blossom end rot.

Irregular irrigation can cause fruit cracking. Mulching with straw or plastic foil would be beneficial but usually it is too expensive. If mechanical harvesting is not planned, staking can be used to keep canopy upright to allow air movement through it which minimizes wetting periods after rainfall or dew and lowers potential for diseases requiring high humidity.