Tomato (Solanum lycopersicum Mill ) is a solanacious plant. The fruit is very rich in essential vitamins and mineral salts (Peet,2001). It generates income to its growers. It is tropical warm season crop, said to have originated in tropical Central and South America(COPR,1983), and it is grown all over Nigeria. The bulk of production is from the dry season cropping particularly under irrigation in the Northern states and near riverbanks in the southern states of Nigeria. According to COPR(1983),the total land area covered annually is over one million hectares with most of the production from the Northern Guinea Sudan Savannah. The area of land used for tomato production in tropical Africa is about 300,000 hectares with an estimated annual production of 2.3 million tonnes. Nigeria is the largest producer with 126,000 hectares and annual production of about 879,000 tonnes ( Van der Vassen et al.,2004). The average yields in local farms range from 5 to 10 t/ha, while 30 t/ha have been recorded in research farms ( Adeyemi, 2010).
Uguru (1996) stated that tomato is a short –lived herbaceous annual with weak trailing much branched stem with hairs at juvenile stage of development. Tomato is a warm season crop that grows well in areas with evenly distributed rain fall and with long period of sunshine. Fruits of local varieties in Nigeria are thin-walled, heavily seeded and sour in taste. Tomato fruits contain high level of vitamins A, B, and C (Erince, 1999). Purseglove (1998) reported that tomatoes were used in large quantities to produce sauce, ketchup, puree and juice. Green tomatoes are used for pickles and the seeds are extracted from the pulp are used in canning industry. Tomato is one of the most important vegetables grown for edible fruits consumption in virtually every home in Nigeria. Its production in South Western Nigeria is concentrated mainly during the hot raining season (Ahmad and Singh, 2005). According to Adelana (1976), tomato is usually grown in Southern part of Nigeria in small holdings in farms and gardens under rainfed conditions while it is grown in the Northern States under irrigation.
Tomato grows well in many types of soils ranging from sandy to the heavy clayey soils (Uguru,1996). Well drained, fertile soils, with good moisture retaining capacity and high level of organic manures are required for the production of tomato ( Tindal, 1998). Soil is generally a favourable habitat for the proliferation of saprophytic and pathogenic micro-organisms, such as viruses, bacteria, fungi, algae and protozoa (Atlas and Bartha,1993). Soil also supports plant life by providing nutrients and mechanical support. It is one of the vast dynamic sites for biological interactions in nature. Many biochemical reactions which result in distribution of organic matter and nutrients normally occur in the soil. Jaraba et al.,(2007) reported that sand to sandy-loam soils are conducive to Meloidogyne species .
The production of tomato is limited by the attack of pest and diseases. This results in acute shortage of the fresh fruits in certain periods of the year. Yield losses are partly attributed to the susceptibility of tomato cultivars to serious pests and diseases (Udo, 2004). More than a hundred different pest species have been recorded worldwide on tomato crops(Peet,2001; Udo,2004). They include nematodes, mites, thrips, aphids, moths, whiteflies, beetles and flies (COPR, 1983; Kessel,2003).
Nematodes are one of the major pests of tomato globally especially in the tropical and subtropical regions. The production of tomato is impaired by among other factors its infections by nematodes (Abubakar et al., 2004). Adesiyan et al.,(1990) reported reductions in yield ranging from 28 to 68%. Over sixty species of plant parasitic nematode attack tomato but the most destructive nematodes responsible for enormous yield losses of tomato are the root-knot nematodes belonging to the genus, Meloidogyne (Sasser 1989. Dufour et al.,., 2003; Udo, 2004).
Udo (2004) stated that about 29-50% overall yield reduction of tomato in the tropics is attributed to the root-knot nematodes. Root knot nematodes (Meloidogyne spp.) are small microscopic roundworm organisms grouped as a major pathogen of vegetable crops throughout the world, affecting the quantity and quality of marketable yields (Kingland, 2001). They infect plant roots by producing galls through their feeding habits (Nesmith, 2000). These nematodes are responsible for a greater yield loss of tomatoes when they infest plants at the seedling stage (Vavring, 1991; Mullins, 2000; Dufour et al., 2003). According to Adesiyan et al., (1990), nematodes can predispose plants to infections, break disease resistance, act synergistically in the development of the disease or are vectors of the disease organisms.
Nematodes in agricultural soils have been controlled using such measures as chemicals like furadan, sincocin and oxamyl which are very expensive and misapplication might result in an adverse effect on the environment. Pyrethriods and other newly developed safer pesticides are expensive. Other control measures like use of biological agents (Verticillium chlamydosporium and Arthrobotrys oligospora), resistant varieties, botanicals, organic manures, crop rotation and time of planting are also employed in controlling plant pathogenic nematodes in the soil. Atungwu (2006) reported that several organic materials have been effectively used for the management of nematode pests of crops throughout the world. Atungwu et al., (2010) stated that although chemical control gives instant reduction of nematodes, its expensive cost forces farmers to exploit indigenous control methods. Other alternative control measures which are cheaper, available and environmentally friendly should therefore be developed and used in controlling nematode attacks on tomato to ensure higher productivity and sustenance of the crop. The objectives of this research are therefore to:
- evaluate the efficacy of some aqueous leaf extracts in controlling root-knot nematode infections on tomato.
- evaluate the effect of different soil amendments in controlling root-knot nematode infections on tomato.
- evaluate the effect of different coloured polyethylene mulches in controlling root-knot nematode infections on tomato.
Tomato, a solanacious crop, originated in tropical Central and South America, but first domesticated in Mexico and later taken to Europe and across the pacific by the early Spanish explorers and Portuguese traders. The crop has increased in popularity in the tropics and sub-tropics and is now the second most important vegetable crop in the area ( COPR, 1983; Taber et al.,1998; Udo, 2004).
Tomato is a herbaceous plant. It is commonly grown as an annual though perennial tomato culture is an established practice in many parts of South America ( Peet, 2001). Atherton and Rudich (1986) stated that the stem is covered with glandular hairs and typically about 4cm in diameter. At the tip of the main stem is the apical meristem, a region of active cell division where new leaves and flower parts are initiated. Kessel (2003), reported that the leaves are covered with hairs and the lowest two or three leaves may be small with few leaflets. Many smaller leaflets or follicles may be interspersed with large leaflets. The leaflets are usually petiolate, serrate-with toothed edges. According to Anaele (2007), tomato plant has a tap root system with lateral roots arising behind the growing root tip. Adventitious roots, similar in structure to the lateral roots, develop in favourable conditions from the stem particularly near the base. The inflorescence of tomato is formed terminally on the shoot. The tomato fruit is a berry composed of flesh (pericarp walls and skin) and pulp (placenta and locular tissue including seeds). The pericarp consists of an exocarp or skin, parenchymatous mesocarp and a single celled layer of endocarp lining the locules. The seed is a flattened ovoid structure about 5mm long, 4cm wide, and 2mm deep consisting principally of embryo, endosperm and testa or seed coat. The embryo comprises the root or radicle, hypocotyl, two cotyledons and the shoot apex.
2.0.1. ECONOMIC IMPORTANCE OF TOMATO
Vietmeyer (1986) posited that tomato is one of the most popular vegetables and ranks 15th among the world food crops. Over 135,000,000 tons of tomato fruits are produced per year and consumed world wide. It contains more vitamins A and C and a good source of iron, thiamine, riboflavin, niacin, potassium and sodium. One medium sized fresh tomato fruit provides 47% Recommended Dietary Allowance (RDA) of vitamin C, 22% RDA of vitamin A and 25 calories (135g). Tomato has good fresh market and also it tops the list of canned vegetables. Tomato farming is also a good income generating enterprise, providing source of livelihood to many farmers around the world.
The leaves of tomato are used medicinally for ear ache, and the fruits as a remedy for diseases of urinary tract (Abbiw,1990). Tomato is used in making salads, tomato soups and sauces (Uguru,1996).
2.0.2. CLIMATIC REQUIREMENTS OF TOMATO
Yields of tomato are generally higher at elevations over 500m. According to Rice et al, (1993), many cultivars are well adapted to cultivation at low elevations, although yields are low due to lack of diurnal temperature variation and to high humidity which encourages diseases. Uguru (1996) reported that tomato is a warm season crop that requires a temperature range of 65 to 85o F (18 to 29oC). Foliage diseases are rampant at higher temperatures with high humidity. Hot dry winds reduce fruit set as flower drop before fertilization. Excessive precipitation during the period does not favour tomato growth.
Slightly acidic to neutral soils with a pH of 5.5-7.5 are suitable. Low soil temperatures retard the growth of seedlings and absorption of minerals (Peet,2001;Kessel, 2003). Peet (2001) reported that tomatoes have high water requirement and when water availability fluctuates, or when it is too high or too low at critical stages, fruit disorders develop.
- TOMATO AND ORGANIC MANURE
In developing countries, continuous cropping on an area over a long period results in the depletion of soil nutrients to the detriment of the agricultural crops. The use of fertilizers therefore becomes imminent. Inorganic fertilizers were therefore employed to supply lost nutrients as nutrient uptake varies with crops. Continuous and misapplication of inorganic fertilizers could lead to environmental hazards. Synthetic fertilizers are costly and most times are not readily available. High cost and scarcity of inorganic fertilizers in developing countries led to renewed interest in use of unorthodox organic materials as nutrient sources for the cultivation of nutrient demanding crops such as tomato.
Organic manures are obtained from such sources as poultry droppings, cow dung, sawdust, rice husk, farm yard manure. Maynard (1991) reported that the yield of nine vegetable crops (except lettuce) fertilized with 50 t/ha of poultry manure was equal to and sometimes greater than that obtained with inorganic fertilizers. Owolabi et al, (2003) reported that sawdust ash manure at 2,4,6, and 8 t/ha increased the number and weight of tomato fruit significantly.
2.0.4. PESTS OF TOMATO
Peet (2001) stated that more than a hundred different pests have been recorded on a world wide basis on tomato crop. At any one time and place however, only a few types are major pests of economic importance. These include nematodes, mites, thrips, aphids, whiteflies, beetles and flies ( Mckinlay, 1992; and Kessel, 2003). According to COPR (1983), nematodes are recognized as one of the major pests of tomato throughout the world particularly on out door tomatoes in topical and sub-tropical regions. Over sixty species representing nineteen genera of plant parasitic nematodes attack tomatoes ( Udo, 2004), but the most destructive are the root-knot nematodes (Meloidogyne spp). All the important nematode pests of tomato are root parasites that are spread in plant and soil materials (Adesiyan et al., 2000; Sasser, 1989). Ogbuji and Okafor (1983) stated that in Nigeria, food crops are usually grown in traditional mixed cropping which could have maize and cassava as major crops, while pepper, okra, tomato, cowpea, and leaf vegetables are minor crops and control of nematode means that the ecological characteristics of such systems must be understood.
2.0.5. ROOT-KNOT NEMATODE LIFE CYCLE
All nematodes pass through an embryonic stage, four juvenile stages (J1-J4) and an adult stage. Juvenile Meloidogyne hatch from eggs as vermiform second stage juvenile (J2), the first moult having passed within the egg. Newly hatched juveniles have a short free-living stage in the soil, in the rhizosphere of the host plant. J2 do not feed during the free living stage, but use lipids stored in the gut ( Eisenback and Triantaphyllou, 1991).
The life span of an adult female may extend to three months and many hundreds of eggs can be produced. Females can continue egg laying after harvest of aerial parts of the plant and the survival stage between crops is generally within the egg. The length of the life cycle is temperature dependent ( Madulu and Trudgill, 1994; Trudgill, 1995). Widmer et al., (2008) stated that in M. javanica, development occurs between 13oC and 34oC , with optimal development at about 29oC .
2.0.6. NEMATODES AND SOIL AMENDMENTS
Application of organic matter is the basis of sustainable nematode control and the maintenance of a healthy soil food (Dufour et al., 2003). There is substantial evidence that the addition of organic matter in the form of compost or manure will decrease nematode pest populations and associated damage to crops (Stirling, 1991). This could be as a result of improved soil structure and fertility, alteration of the level of plant resistance, release of nemato-toxins, or increased populations of fungal and bacterial parasites and other nematode antagonistic agents. Some sources of organic matter known to be nematode-suppressive include oil cakes, sawdust, sugarcane bagasse, bone meal, horn meal, compost and certain green manures ( Dufour et al., 2003). Abuabakar et al., (2004) observed that there was decrease in number of root-knot nematodes and increase in the growth of tomato when cow dung and urine were combined. Similar observations had been made by other workers (Babalola, 1990; Akhtar and Alam, 1992; Alam et al ., 1994).
2.0.7. MELOIDOGYNE SPECIES AND TOMATO
Adesiyan et al., (1990) reported that tomato, one of the popular vegetables in Nigeria, is affected adversely by Meloidogyne spp. of nematode; of which M. arenaria; M. incognita; and M. javanica are widely distributed in the country. An estimated overall average annual yield loss of the world’s major crops due to damage by plant parasitic nematodes has been put at 12.23% (Sasser, 1989). According to Fortnum et al., (1991), the overall impact on tomato is variable, as disease intensity is influenced by many biotic and abiotic factors thereby causing galls or root-knots on infested plants, other symptoms include stunted growth, wilting and poor fruit yield. M. javanica on its own is estimated to cause 50% loss in economically important vegetables and fruit crops in the tropics annually (Agrios, 1997).
2.0.8. AQUEOUS EXTRACTS IN CROP PROTECTION
The use of aqueous extracts in disease control is eliciting much interest in developing countries due to high cost of synthetic pesticides and their hazardous residual effects on the environment. Tovignan et al., (2001) stated that the use of synthetic chemicals in disease control is eliciting much concern owing to the undesirable effects emanating from their use. According to Salako (2002), this is rekindling a renewed interest in the use of natural products from higher plants in the disease management scheme. Schmutterer (1990) stated that it is of paramount importance not only for the developing countries but also for the industrialized world to find effective method to stabilize and if possible increase food production in third and fourth world countries. Dudu and William (1991) reported that considering the high cost of synthetic pesticides, threat to human health as a result of their effects and pollution of the environment, there is need for further research into the use of plant extracts as alternatives to synthetic pesticides.