Tomato (Lycopersicon esculentum Mill) belongs to family solanaceae and is grown profitably throughout the world including Pakistan. It was originated in the highlands of the west coast of South America with native name tomati. Tomato is grown in outdoor fields, greenhouses and net houses. The tomato crop is very versatile and its consumption is increasing quite rapidly day by day especially in developed countries while it has become important part of the food basket in developing countries. It is an important kitchen crop of Pakistan and is grown on 53150 hectares with the production of 536217 tons and average yield of 9.93 tones/ hectare which is very low as compared to USA with 76.13 tones/ hectare. It is cultivated in all provinces of Pakistan but its production is mainly concentrated in Sindh and Punjab.
Tomatoes are considered as good appetizers. The use of tomato is also very helpful for diabetic patients and exerts a better effect on urinary acidity as compared to orange juice. Hundred grams of edible parts of tomato contain 0.9 g protein, 94.1 g water, 3.5 g carbohydrates, 0.1 g fat, 15-20 calories energy, 500-1500 IU Vitamin A, 0.1 g thiamin, 0.02 mg riboflavin, 20-25 mg vitamin C, 0.1-0.3 mg iron and 6-9 mg calcium. Tomato is highly valued for its nutritional value as it contains vitamins and minerals. The tomato is an excellent source of vitamin C (one medium tomato provides 40% of the RDA) and a good source of vitamin A (20% of the RDA). Vitamin A is important for bone growth, cell division and differentiation and helps in regulating immune system and maintaining surface linings of eyes, respiratory, intestinal and urinary tracts. Vitamin C is important in forming collagen, a protein that give structures to bones, cartilage, muscle and blood vessels. Tomato is a very helpful in preventing and curing of cancer and according to various studies it is concluded that the people eating tomatoes are rarely affected with cancer. Tomatoes are also good source of lycopene. Lycopene contents are about 20% found in tomato. Tomato like other field crops is facing so many pathogenic problems, of which Meloidogyne spp. is the most serious problem.
This nematode was first discovered in a green house on cucumber in England and it was later discovered in Holland. Root-knot nematodes are considered as threat to cultivated fields due to severe root damage of crops in Caribbean. On global basis, M. incognita has been reported to constitute about 47% of the total root-knot nematodes population. M. incognita was found to be a most damaging pest of various vegetables all over the world as well as in Pakistan by causing remarkable yield losses of 30 % to vegetable crops.
Meloidogyne incognita is the major threat to vegetables in Pakistan and also the most widespread and economically important in Punjab province. During a survey it was found 85.10 % occurrence of these species associated with vegetable crops in the Punjab. Meloidogyne incognita can cause losses from 14 to 44% in tomato under plastic tunnels, whereas in Punjab its losses are also very high 23%. Meloidogyne javanica and M. incognita are the dominant species associated with banana, papaya, sugarcane, cabbage, okra in Sindh, Punjab and NWFP.
The degrees of susceptibility of various host plants vary by making them either highly susceptible or less susceptible or resistant to M. incognita. The susceptibility of root knot nematodes depend on the juveniles that penetrate into the roots of susceptible host plants and formation of giant cells takes place which later named as knots and reduction in production occurs.
The effects of Meloidogyne incognita on plants may be either direct or indirect. Direct effect includes direct feeding that restricts the supply of water and other nutrients essential for plant growth. Giant cells are formed that restrict supply of water and nutrients through xylem and phloem vessels and ultimately death of root tips occurred. The nematode root infection renders plants unfit to absorb water and nutrients and other essential elements from soil leading to reduced vigor and less production. In case of indirect effects, host resistance mechanism is broken and physical entry sites are created for pathogens and susceptibility to foliar disease is increased and causing yield losses of 46.2% in tomato, 99% in okra and 27.3% in brinjal.
The above ground symptoms are; reduced growth and fewer, small, pale green or yellowish leaves that tend to wilt in warm weather. The presence of M. incognita cannot be diagnosed by aboveground symptoms alone. Underground parts of the plants show characteristic symptoms of the disease. Swelling of infected roots takes place at the point where invasion and develop of nematode occurs leading to formation of galls due to which diameter of healthy root is increased several times. Clubbed and rough appearance also occurs in several infections on the root. Abnormal swellings can easily be seen on the roots when carefully dug from affected plants and removing the soil gently from the root systems. Several short root branches are also developed along with galls on roots infected with nematodes as a result bushy root system is appeared. Particularly in late season, infected roots usually develop rotting, small in size and show symptoms of necrosis also.
Meloidogyne incognita causes a destructive harm to the crop and its control through the chemicals, apart from being very expensive is not very effective. Alternatives to chemical nematicides include the use of crop rotations, fallow periods, and organic amendments. Crop rotation is widely used and very effective as compared to continuous cultivation of susceptible crops. Nematodes with narrow host ranges can be controlled by infrequently growing host crops in rotation with non-host crops such as bahia grass (Paspalum spp.) or pangola grass (Digitaria eriantha), or by using strip-tillage in existing bahia grass pasture .
Various nematode management strategies are being used. Among these strategies nematicides are considered the most effective. Nematicides in chemical form are effective against nematodes in very rapid manner. Non-fumigant nematicides are the most important control agents for phyto-parasitic nematodes attacking vegetable crops. Most of the recent studies have evaluated different combinations of fumigants such as 1,3-dichloropropene (1,3-D), metham-sodium (MS) and chloropicrin against the standard Methyl bromide.
Control using crop rotation is more difficult for nematodes with wide host ranges, such as M. incognita; where the choice of non-host crops may be limited and not economically feasible; where mixed populations of nematodes occur. Both non fumigant and fumigant chemicals are effective against nematodes. The use of chemicals only should be practiced where crop rotation is not possible or resistant varieties are not available.
The practical solution of the problem is in the development of resistant varieties or finding out biological control of the pathogen through the use of antagonistic organisms in spite of chemical control. Disadvantage of chemical control is that it gets more expensive every year and less effective as resistance develops and also causes pollution, kills the natural enemies also, so that to avoids all these problems create by chemical control alternative method of biological control is being used because advantage of biological control is that it decreases disease intensity leading to higher population, reduces the use of chemical fungicides and nematicides and it is safe for the users and the farming community. Chemicals are environmentally unfriendly; causing groundwater contamination, toxicity to farmers, poor target specificity and causes ozone layer depleted.Desaeger and Rao, 2000 J. Desaeger and M.R. Rao, Infection and damage potential of Meloidogyne javanica on Sesbania sesban in different soil types, Nematology 2 (2000), pp. 169–178. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (6) Attention is turning towards an integrated management approach: incorporating host plant resistance, nematicidal or antagonistic plants, bio-control agents, cultural practices and bio-products to check the nematode populations that they may remain below the level of economic threshold.
Bio-products (Bio-pesticides) are pesticides that are derived from various natural materials as certain minerals, plants, animals and bacteria. For example, baking soda, mint and garlic and other bio-pesticides (Emamectin, abamectin and biosal) are also considered as bio-products as they have pesticidal applications. Approximately, 700 products, active ingredients and 175 registered bio-pesticides were there at the end of 1998.
Bio-products are important tools in animal health and crop protection.Bio-products are naturally less harmful than chemical pesticides. Bio-products are specific in their action and affect only one target pest or in some times, many target organisms while conventional pesticides affect many organisms such as insects, mammals and birds. Bio-productsas compared to conventional pesticides decompose quickly, effective in very small quantities and thus results in less exposure and also avoid health problems. Bio-products can be the best alternative of conventional pesticides when used in Integrated Pest Management (IPM) programs for high yield of the crops.
As biological control, the use of bio-pesticides against plant parasitic nematodes is the most effective and environment friendly method. So, the use of bio-products in integrated pest management (IPM) is now accepted as an ecologically sound and economically viable alternative to chemical pest control.