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Okra (Abelmoschus esculentus L.) is locally known as Bhindi is one of the most important summer vegetable crops in Pakistan. Okra, the genus esculentus with synonyms Abelmoschus belongs to the family Malvaceae or mallow under the order of Malavles. This genus contains about 150 known species with esculentus as the specie of okra (Thompson and Kelly, 1957). Okra is an allopolyploid of tentative parentage. Truly wild, as divergent to naturalised, populations, are not definitely known, and the species may be a cultigen. Its beginnings were in Ethiopia and it was cultivated by the ancient Egyptians in the 12th century B.C. It then made its way through North Africa and the Middle East (George, 1985). It is now grown in all parts of the tropics and during the summer in the warmer parts of the temperate region (Baloch, 1994). It is one of the oldest cultivated crops and presently grown in many countries and is widely distributed from Africa to Asia, southern Europe and America (Ariyo, 1993; Oyelade et al., 2003).
Its total production is 4.8 million ton pods of Okra in the world; India contributes 70%, Nigeria 15%, Pakistan 2%, Ghana 2%, Egypt 1.7% and Iraq 1.7% (Gulsen et al., 2007). In Pakistan the total area under Okra cultivation is about 14.78 thousand ha and total production is about 0.112 million tones with average yield of about 7.55 tones/ha of green pods (Anonymous, 2008).
Okra plant is a semi woody, fibrous herbaceous annual with an indeterminate growth habit. It is a perennial plant that grows up to 2 meters tall with heart shaped leaves and large, yellow flowers. The leaves are 10-20 cm long and broad, palmately lobed with 5-7 lobes. The flowers are 4-8 cm diameter, with five white to yellow petals, often with a red or purple spot at the base of each petal (Purewal and Randhawa, 1947). The seed pod which range in size from 3-10 inches in length and have a unique, sticky texture and sweet flavor. The plants form a deeply penetrating taproot with dense shallow feeder roots reaching out in all direction in the upper 45cm of the soil. The seeds are dicotyledonous and kidney shaped with epigeal germination (Nonnecke, 1989). Okra is mainly a self pollinated crop however; insects such as honey bees and bumblebees do cross-pollination occasionally. The seed pods rapidly become fibrous and woody and must be harvested within a week of the fruit being pollinated to be edible. The fruits are harvested when immature and eaten as a vegetable (Pecknepaugh, 1991).
It is among the most heat- and drought-tolerant vegetable species in the world. But severe frost can damage the pods and will tolerate poor soils with heavy clay and intermittent moisture. Most cultivars are adapted to high temperature throughout the growing period with little seasonal fluctuation. Seed will only geminate in relatively warm soils, no germination occurs below 16oC. A monthly average temperature range of 21oC to 30oC is considered appropriate for growth, flowering and pod development (Tindall, 1983; Nonnecke, 1989).
Okra has high food value and rich in some nutritional elements (Ca, Mg & P) also contains some vitamins with medium percentages (Riboflavin, Thiamin, Vitamin-C & Vitamin-A) (Matloob et al., 1989). Which can help in minimizing their deficiency in the daily diet. Okra is used for sacks and ropes (Watt, 1908), biogas and fuel (Dahiya and Vasudevan, 1987) and also stem could serve for paper-making (Martin, 1982). Young leaves of okra which are cooked by the Africans may also act as a diuretic, and abortifacient as well as having gastric ulcer and wound healing properties (Weniger and Robineau, 1988). Flower buds are also consumed as vegetables (FAO, 1988). The fruit mucilage is of interest as it could replace blood plasma (Benjamin et al., 1951), reduce fluid friction in turbulent flow (Castro and Neuwirth, 1971), and stabilize foams (Woolfe et al., 1977) and suspensions (Wahi et al., 1985).
It also has medicinal properties as an emollient, laxative and expectorant (Muresan and Popescu, 1993). Okra is also rich in phenolic compounds which reduce the risk of cardiovascular diseases, neurodegenerative diseases and certain cancers (Havsteen, 2002; Romani et al., 2005). Okra seeds are a source of oil, protein and can be used as a substitute for coffee (Martin, 1982). Okra seeds contain Protein content 20 percent or more and oil content 14 percent or more. Okra seed oil is rich in unsaturated fatty acids such as linoleic acid (Savello et al. 1980), which is essential for human nutrition. While the seed powder has been used as a substitute for aluminium salts in water purification (Vaidya andNanoti, 1989).
Growth and yield depend upon many factors including seed quality, nutrition, climatic conditions and cultural practices. Plant growth regulators are chemical substances and when applied in less amounts, they bring rapid changes in the phenotypes of the plant and also influence the growth, right from seed germination to senescence either by enhancing or by stimulating the natural growth regulatory system (Das and Das, 1995). Growth regulators can improve the physiological efficiency including photosynthetic ability and can enhance effective partitioning of the accumulates from source-sink relationship and stimulate the translocation of photo-assimilates, thereby increasing the productivity in field crops (Solaimalai et al., 2001). Though, the plant growth regulators have great potential, it has to be sensibly planned in terms of optimal concentration, stage of application, species specificity and seasons. These are considered as new generation of agro-chemicals after fertilizers, pesticides and herbicides. In their wide spectrum of effectiveness on every aspect of plant growth, even a modest increase of 10-15 per cent could bring about an increment in the gross annual productivity by 10-15 m tons. Plant physiologists have recognized five well defined groups of plant growth substances. These are auxins, gibberellins, cytokinins, inhibitors (ABA) and senescent hormone ethylene. The use of plant growth regulators had led to intensive scientific activity for their commercial exploitation. Since, 1949 many beneficial effects of different plant growth regulators have been reported on different horticultural crops and other field crops. Among them, the use of GA3, NAA and ethrel is of considerable interest in different fields of agriculture and horticulture (Briant, 1974).
. Growth regulators were first identified in the early 1930ââ‚¬â„¢s as significant tools in increasing crop production. The growth and flowering of many flower crops and bedding plants were successfully controlled by growth regulators to produce high quality horticultural products. Gibberellins (GAs) play an essential role in many aspects of plant growth and development, such as seed germination (Maske et al., 1997), stem elongation and flower development (Yamaguchi and Kamiya, 2000). And increased vegetative growth in plants sprayed with GA3 (Wareing and Phillips, 1976). Gibberellic acid is a simple gibberellin, promoting growth and elongation of cells. It affects decomposition of plants and helps plants grow if used in small amounts. It stimulates the cells of germinating seeds to produce mRNA molecules that code for hydrolytic enzymes (Bidwell, 1974). Naphthalene acetic acid (NAA) is a plant hormone of the auxin family. It is one of the synthetic auxin that enhances ethylene synthesis in treated flowers and young fruits, which in turn induces abscission of those organs (El-Otmani et al., 2000). And also used as a practical growth regulator and is an ingredient in many commercial plant rooting horticultural products and inhibition of flower drop, bud bole shedding, button shedding and inhibit sprouting and development of suckers (Williams and Taji, 1989).
Effect of plant growth regulators applied in the earlier stages of plant life have shown beneficial effects on the vegetative growth as well as on the yield of the plant. The growth regulators influence plant growth and development at very low concentrations while they inhibit at high concentrations (Jules et al., 1981).
Foliar application of growth regulators and chemicals at flowering stage may improve the physiological efficiency and may play a significant role in raising the productivity of the crop (Dashora and Jain, 1994). Foliar application of plant growth regulators increased plant height, number of leaves per plant, fruit size and seed yield in ground nut and many other crops (Lee, 1990).
Therefore the purpose of present study will not only to enhance the growth but also to increase the productivity of okra by using different growth regulators and their combinations.