ABSTRACT

The experiment was conducted at the Teaching and Research Farm and Laboratory, of the Department of Crop Science, University of Nigeria, Nsukka to: (i) determine the fruit characteristics, agronomic, yield and yield component trait performances of seven tomato varieties; (ii) produce and select genotypes that combine adaptable and qualitative traits of interest; (iii) determine the inheritance pattern of the crop traits; (iv) estimate heterosis and heritability in the hybrids, and (v) determine the combining ability of the selected parents and their hybrids. The experimental materials used were the seeds of six varieties of tomato including; Grosso (G), Insulata (In), Petomech (P), Chico ІІI, Super Roma, and Piccolo obtained from Italy and Lycopersicon pimpinellifolium; wild(W) obtained from Mbu in Isi-uzo Local Government Area of Enugu state. General combining ability of the parents and the specific combining ability of the hybrids were estimated using Griffings’ model 1 method 2 in a 4 x 4 diallel cross. Chi- square statistic was used to test for the inheritance pattern of these traits. The wild parent was significantly (p = 0.05) higher in number of flowers/truss (10.07), fruits/truss (7.33), fruits/plant (621), and fruit yield (11.96 tons/ha) than the other parents. Petomech was significantly (p = 0.05) higher in pericarp thickness (5.35 mm), days to first fruit spoilage (24), 50% fruit spoilage (34) and 100% fruit spoilage (65) than the other parents. Grosso showed significantly (p = 0.05) higher average fruit weight (67g) and fruit length (9.69 cm) than the other parents. The cross, W x P was significantly (P = 0.05) higher than other hybrids and the parents in fruit yield (27.41 tons/ha) and number of fruits/truss (8.43). The cross, In x P was significantly (P = 0.05) higher than the other crosses and hybrids in days to first fruit spoilage (46). The cross, W x G was also significantly higher than the other crosses and the parents in days to 100% fruit spoilage (86) and it was statistically similar to Petomech. The wild was the best general combiner in days to flowering (2.47), fruiting (2.71), ripening (2.61) and fruit yield (9.22). Petomech was the best general combiner in days to first fruit spoilage, 50% fruit spoilage and 100% fruit spoilage (5.08, 4.23 and 9.77, respectively. The cross, W x P was the best specific combiner in number of flowers/ truss (1.38), fruits/truss (1.91), fruits/plant (79.85), and fruit yield (21.67). The cross, In x P was the best specific combiner in pericarp thickness (1.77 mm).Highest better parent heterosis (BPH) was recorded in W x P for number of fruits/truss (12.94 %) and fruit yield (206.04 %). Highest BPH was also recorded in W x G for days to first fruit spoilage (233.65), 50 % spoilage (225.15 %) and 100% spoilage (262.87 %). Hybrids having wild as one of its parent had low disease incidence and severity at fruit ripening. W x P had significantly higher phenol content (4.29 mg/100g) and flavonoid (2.62 %) content than all the parents and the other hybrids.

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INTRODUCTION

Tomato (Lycopersicon spp, 2n=24) belongs to Solanaceae family and it is of the genus Lycopersicon which ranges from self-incompatible species to self- compatible species (Rick et al., 1977; Miller and Tanksley, 1990). Tomato originated from the South American Andes (Shankara et al., 2005) from where it spread to other parts of the world following its introduction to Europe by the Spanish conquistadors. Tomato is one of the most important vegetables in the world. It is the second most consumed vegetable in the world behind potato (FAO, 2008). World production of tomato in 2008 was 130 million tonnes where China led the production with about 33,811,732 tonnes, while Nigeria ranked 13th with about 1,701,000 tonnes (FAO, 2008). The bulk of tomato production in Nigeria comes from the Northern states. This is due to the presence of enabling environmental conditions such as low rainfall, diurnal range in temperature, relatively dry climate, low relative humidity, low pest and disease incidence which allows the growth and development of the crop in that region. Rainfall and its associated effects on the yield of tomato, such as reduction in the number of flowers as a result of flower abscission can be considered as a major problem in tomato production (Weerakkody and Peiris, 1997). Diseases such as mould, damping off and blossom end rot that proliferate under high humidity, low temperature and insufficient drainage would cause yield and quality loss in tomato plant (Hessayon, 1985). Foliage diseases are rampant at high temperature and high relative humidity, often increasing losses in terms of yield (Uguru and Igili, 2002). Excessive rainfall encourages the spread of certain fungal and bacterial diseases on tomato plants (Geisenberg and Stewart, 1986). Disease incidence on susceptible tomato plant is dependent on moisture and temperature. The disease causing organism is most destructive during wet weather (Yang, 1978). Uguru and Atugwu (2001) observed low performance and low fruit set due to excessive flower and premature abortion. These are the prevailing environmental conditions of the South Eastern states of Nigeria.

The varieties used for production in South Eastern states of Nigeria have varying problems. Some of them have been shown to have high water content, medium to small sized berries that crack easily, short shelf life and susceptibility to insect and disease (especially fungal and bacterial) attack. Common ones include; Nsukka Local, Roma VF, and Tropica.

Lycopersicon pimpinellifolium (currant tomato) has very small fruits that are rich in vitamin A and lycopene. It also has good flavour, taste and tolerates heavy rainfall and drought

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conditions as well as high humidity and disease infections. It remains a good source of gene for adaptability, improvement of fruit quality and disease resistance to common foliage diseases of tomato. The wild tomato possesses some undesirable horticultural characteristics principal among which is the small fruit size, (Tanksley et al., 1996). Some exotic tomato varieties like, Petomech and Insulata, have relatively good market sizes, firm and less watery flesh and long shelf life after harvest. Grosso variety has large fruit size. Despite the good qualities of the exotic varieties, most of them are known to exhibit low adaptability/ tolerance to the environment and are prone to insect pests and disease attack.

Thus a breeding programme that will combine the good qualities of the exotic and the wild variety will evolve genotypes that will combine adaptable features with good quality traits.

The objectives of the study were to:

I.          determine the fruit characteristics, agronomic, yield and yield component trait performance of seven tomato varieties,

II. produce and select genotypes that combine adaptable and qualitative traits of interest, III. determine the inheritance pattern of the crop traits,

IV.

V.

estimate heterosis and heritability in the hybrids,

determine the combining ability of the selected parents and hybrids.

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LITERATURE REVIEW

Tomato (Lycopersicon esculentum Mill) belongs to the Solanaceae family. There are nine species in the genus Lycopersicon (Taylor, 1986; Warnock, 1988). The genus Lycopersicon has species that are both self- compatible and self- incompatible. Cultivated tomato is self-fertile whereas the others are self-incompatible except Lycopersicon pimpinellifolium which undergo various degree of self- fertilization (Simpson and Ogorzaly, 1986). Various self - compatible species vary in their rate of out crossing, making them ideal for the study of mating system evolution (Michael et al., 2002).

Environmental requirements of tomato

Temperature

Tomato requires a relatively cool dry climate for high yield and premium quality (Shankara et al., 2005). The plant can survive different types of environment, ranging from temperate to hot and humid tropical conditions. Temperature need varies with the phase of growth. For germination, the ideal temperature is 16- 29oC (Henriques et al., 2008). Most varieties require an optimum temperature range between 12oC and 24oC for vegetative growth and 24oC day temperature, 14- 17oC night temperature for fruit set. Plant tissues are damaged below 10oC and above 38oC (Shankara et al., 2005). High temperatures accelerate the development of fruit, reduce the time necessary for its maturity and its size (Dorais et al., 2001). If cool or hot weather persist during flowering, pollen production will be low thus reducing fruit formation (Shankara et al., 2005). Furthermore lycopene responsible for the intense red colour of the fruit is produced more at temperatures between 20- 24oC in the day and 18oC at night (Henriques et al., 2008) while temperatures above 20- 24oC inhibit its production and favours the production of other carotenoids which give a yellow orange colour to the fruit (Henriques et al., 2008).

Rainfall and relative humidity

Water stress and long dry period will cause bud and flowers to drop off and the fruit to split (Shankara et al., 2005). Heavy rain and high relative humidity encourages the growth of mould which results in rotten fruit. High relative humidity leads to a decrease in plant transpiration and a decrease in nutrient absorption (Dorais et al., 2001). Low relative humidity (15- 22 %) reduces photosynthetic ratio because of the close up of the stomata (Henriques et al., 2008). It also leads to reduction in growth, fruit size, and total production (Henriques et al., 2008). In periods of little rainfall, irrigation at an average of 1- 2 times per

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week before fruit set and 2- 3 irrigation after fruit set per week with heavy soaking is needed (Anon, 2002). Lack of soil moisture will produce fruit with blossom end rot (Anon, 2002).

Soil

Tomato requires a well-drained sandy loam soil, with a soil depth of 15- 20 cm that has a permeable upper layer (Shankara et al., 2005). Tomato grows well in soil with pH of 5.5- 6.8 with adequate nutrient supply. Soils with very high organic matter content are less suitable for production during rainy season due to their high water holding capacity and mineral deficiency (Shankara et al., 2005).

Botany of tomato

The stem of tomato is a vine which can be either determinate or indeterminate; this is based on whether the apical stem terminates in an inflorescence or not. Determinate cultivars are bushy with restricted flowering and fruiting and are suitable for field conditions (Picken et al., 1986). The main stem of the indeterminate cultivars grows indefinitely, reaching more than 10 m in a year’s growth in a greenhouse (Picken et al., 1986). Tomato plant produces a deep tap root with extensive secondary roots. The seeds are 3-5 mm long and 2-4 mm wide, numerous, kidney or pear shaped. They are flat and have grey and slightly hairy seed coat with the embryo coiled up in the endosperm (Shankara et al., 2005). The leaflets are covered with glandular hairs and are ovate to oblong in shape. Small pinnate appears between larger leaflets. The flowers are bisexual, regular and found opposite or between the leaves. It has a short and hairy calyx tube and persistent sepals. There are six yellow petals of about 1cm long. The stamen are six in number, the anthers are bright yellow and surround the style with an elongated sterile tip. The stamens are fused with the lower part of the corolla forming a stamina cone. The ovary is superior with 2-3 compartments (Atherton and Rudich, 1986). The fruit is a fleshy berry with shape ranging from globular to oblate and diameter between 2- 15 cm. Immature fruits are green and hairy while the ripe ones could be orange yellow or red in colour. It is usually round, smooth or furrowed. Pollens are usually released before elongation of the style through the stamina cone. Temperature has a major effect on this process. If temperature is below 150C and above 290C, there will be restriction on the release of pollen resulting in incomplete fertilization of ovule (George, 1985). This causes the cell wall to collapse leading to deep indentation of the fruit, a situation called ‘cat face’. The best shape and fullest fruit is as a result of complete fertilization of the ovules (George, 1985).

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Chemical qualities of tomato

Tomato is very important in human diet. It is rich in minerals, vitamins (A, B, C and E), essential amino acids, sugars and dietary fibre. Other red fruits and vegetables can also be sources of lycopene (Edinger, 2005) but tomato and its derived products are the highest source of lycopene in human diet (Takeoka et al., 2001). It contains high concentration of carotene that depends on time of harvest, geographical location and genotype (Dorais et al., 2001). Tomato is made up of 93- 95% water. The remaining 5- 7% consist of inorganic compounds, organic acids (citric and malic), sugar (glucose, fructose and sucrose), proteins, cellulose, and lipids (Giordano and Silva 2000). Tomato is a major and excellent source of nutrient and phytochemicals (Edinger et al., 2008).

Phytochemicals

Phytochemicals are chemical compounds produced by plants to protect them against pathogens. Some phytochemicals are produced only after the plant has been attacked by herbivore or pathogens (Wittstock and Gershenzon, 2002) while others are inherent in the plant. Many of the individual constituents of essential oils are very toxic to insects (Isman 2000) and to pathogens (Cox et al., 2000). Some of these phytochemicals include phenols, flavonoids, tannins, and alkaloids.

Plants have the ability to synthesize a large number of aromatic substances, most of which are phenols or their oxygen-substituted derivatives (Cowan, 1999). Phenol offers resistance to plants (Sadasivam and Manickam, 1992). Most of them have antimicrobial activity (Kondo and Kawashima, 2000). Most are secondary metabolites, which may be in the form of simple phenols and phenolic acids, quinones, flavones, flavonoids, flavonols, tannins, terpenoids, essential oils, and alkaloids (Cherif et al., 2007). Phenolics are characterized by at least one aromatic ring (C6) bearing one or more hydroxyl groups (Michalak, 2006).

Flavonoids are low molecular weight polyphenolic secondary metabolic compounds found in green plant kingdom and it is located in the vacuole of plants (Amalesh et al., 2011). They protect plants against biotic and abioti