Genetic Differences of Germplasm more Valuable in Identification of the Genotypes

Genetic Differences of Germplasm more Valuable in Identification of the Genotypes: Adapted to Perform Well under Saline Environment

Noman Naseer¹, Rashad Mukhtar Balal¹, Muhammad Adnan Shahid^1,3_, Muhammad Zubair¹ and Mujahid Ali²

1. Department of Horticulture, University College of Agriculture, University of Sargodha
2. Institute of Horticultural Sciences, University of Agriculture, Faisalabad
3. Horticultural Sciences Department, Institute of Food & Agricultural Sciences, University of Florida, Florida, USA.

Agriculture is considered as back bone of Pakistan’s economy (Akram et al., 2011). It is the second largest sector of Pakistan which imparts more than 20.9% of its GDP and it hire 45% employs of a country. Upon 62% of Pakistanis relies on agriculture (Nadeem et al., 2011). In agriculture, cultivation of vegetable has additionally highest advantages and beneficial business enterprises because it can be utilized fresh and of higher cost. Vegetables are of short duration crop and having different structure like roots, tubers, leaves and flowers for utilization. Cucurbitaceae is a vast family includes 118 genera and 845 species (Mabberley, 1997). Musk melon (Cucumis melo L.), Bottle gourd (Lagenaria siceraria L.) and Squash (Benincasa fistulosa L.) belong to family Cucurbitaceae. These family members have crawling vines with round to elliptical shaped fruits which are utilized for food either in cooked or in fresh form. Due to laxative effect, their fruits and seeds are used to treat constipation (Yang & Walters, 1992).

Area and production of vegetable is increasing day by day as human demand increase for it. Vegetable production in 2011 in world is 1012524.165 tons and area is 53977.066 ha (F.A.O. 2011). In Pakistan area of vegetable was 253.8 thousand acres and production is about 3136.8 thousand tones according to statistical analysis in 2007-2008 (Khalid et al., 2008). Area under cucurbits production in Pakistan is about 62668 hectare and production is 390905 tones. Overall production of melon including cantaloupes in world is about 29,394,542 tones while in Pakistan is about 233,528 tones. China got first position in melon production with 14,336,814 tons of creation while Turkey comes at 2^nd position with generation of 1,699, 550 tones. Pakistan falls at 17th position in melon including cantaloupes production (F.A.O. 2016). Mostly vegetables are in nature low in fat and calories. Not any have cholesterol. These are important source of a lot of nutrients, including potassium, dietary fiber, foliate, vitamin A and C (Anonymous, 2017). Vegetables have high yield Per acre. These are key source of farm earnings. These have high aesthetic importance. More vegetables can be cultivated in one year. Vegetables are sold at big cost than other crops. It required regular work throughout the year hence produce labor opportunity. Some vegetable can be grown two or three time annually. Various green vegetables become ready for harvesting within 50-60 days. (Anonymous, 2015).

Cucurbits are important as nutritional and medicinal point of view containing calories, carbohydrates, dietary fiber, fat mostly less than 1%, vitamin A, B, C, D, E, calcium, iron, zinc, potassium and magnesium. These have cooling effect on body during summer season when consumed. These lower the blood pressure. These lower the problems of heart attack. These are also used for constipation. These are also recommended for diabetic patients. These are also used for decoration purpose. Musk melon is considered the power house of health. Due to fibrous material they are used for constipation. These also have cooling effect. Oil is also extracted from their seeds which have beneficial effect on body. Per 100 gram melon supplies 34 calories, 68% Vitamin A, 61% Vitamin C, 90% water, 9% carbohydrate and less than 1% of fats and proteins (Desai, 2004). Bottle gourd when consumed with lime juice it treated burning sensation in urinary passage. It is also helpful for constipation. Due to low fat content it is highly recommended for diabetic patients. It is also helpful in weight loss. Per 100 grams bottle gourd provides energy of 15 kcal, carbohydrate about 3.69g, fat 0.02g, dietary fiber1.2g, protein 0.6g, vitamin C 8.5 mg, vitamin B1 0.029 mg, calcium 24 mg, Potassium 175 mg, zinc 0.7mg, phosphorus 13 mg and Magnesium 11 mg (Erickson et al., 2005). Bottle gourd is also used in making utensils and musical instruments (Chatterjee & Maitra, 2014). Squash prevent the risk of heart failure. These are also used for weight loss. These are good in prevention of cancer. These also make the bones healthy. Squash contain 45 kcal, carbohydrate 11.69 g, dietary fiber 2g, Fat 0.1g, Protein 1g, Vitamin C 21g, Vitamin 1.44 mg, Calcium 48mg, iron 0.7 mg, zinc 0.15 mg, Potassium 352 mg and Magnesium 34 mg per 100 gram (Anonymous, 2001).

Many biotic and a-biotic factors are responsible for cucurbit’s short production in Pakistan. The factors including cultural practices followed by growers, favorable environmental conditions for disease development, lack of knowledge for epidemiology and its control, use of uncertified seeds and weeds production in the field. The solution of above mentioned problems are using of good cultural techniques, to create awareness in farmers about pathogen and to buy seeds from certified department.

Globally fertility of soil is decreasing due to continuous degradation through erosion, nutrients depletion, water scarcity, acidity, salinization, organic matter depletion and poor drainage (Cakmak, 2002). One of the major factors is salinity which accountable in low productivity of a number of crops in arid and semiarid zone. Globally 800 million hectare of land becomes useless due to salinization in which 437 million hectares is deteriorated due to sodicity (F.A.O. 2005). Throughout the world, Saboora & Kiarostami (2006) warned about a precarious trend of a 10% increase per year in salinity areas. Atleast 50% irrigated land is currently destructed by salinity (Hu & Schmidhalter, 2005). Salinity affected area in South Asia is about 87.6 million hectare (Khan et al., 2003). In Pakistan salt exaggerated area is near about six million hectare, which become a main problems in cultivation of major as well as miner crops especially vegetables (Pakistan Economic Survey, 2007-2008).

Salinization is described as accumulation of salts to a toxic level in soil. The unit used for its measurements is electrical conductivity (EC) On the basis of this unit soil could be described as saline soil or sodic soil. Mostly saline soil has electrical conductivity above 4 dSm^-1 (Ghassemi et al., 1995). There are two different ways of salinization Primary or natural salinization is due to: a) invasion of highly salinised water from sea and ocean in coastal region: b) Aeolian: c) suspension of soil parent material. While secondary or anthropogenic salinisation is due to fertigation, de-vegetation and application of organic or inorganic soil amendments (Biggs et al., 2010; Rengasamy, 2006). The over use of brackish water for irrigation, salt accumulates in root zone of plants which cause low yield and deteriorate plants quality. Shah, (2007) reported that at form level at least 50% using of irrigation water by farmer is ground water whose quality as compared to canal water is low. According to (P.C.S.T, 2003) in Pakistan about 562,000 private and 16,000 public tube wells are using by farmers for irrigation, in them 70% tube wells are pumping brackish water which is unfit for irrigation of vegetables as well as agronomic crops.

Salinity causes two types of stress on plants as osmotic stress and ionic stress. In osmotic stress low water potential in soil is due to high amount of sodium ions while ionic stress is caused by large amount of lethal ions in plant root zone area (Munns & Tester, 2008). Salinity effects morphology, anatomy and entire metabolic system of plants (Kusvuran et al., 2007). When salt amount rises in soil solution and water quantity decreases then osmotic potential of plant cell also decreases which results in slow rate of cell division and cell elongation. Photosynthetic process also slows down. If that condition is continue to exist then chances of plant death also increases (Kusvuran et al., 2007; Ashraf, 1994). Different plants show different characters in salt stress condition depending on them how much they bear the salinity. The initial stage which plant shows under salt stress condition is decline in shoot and root growth (Kusvuran et al., 2007). During Seed germination water is absorbed by the seed and spindle embryo elongation occur (Bewley & Black, 1994). Seed germination procedure is exaggerated by different unfavorable factors such as salinity, which is one of the major a-biotic stresses disturbing plant growth and development, especially in arid and semi-arid regions (Chinnusamy et al., 2005; Cony et al., 2006). It become difficult for seed to germinate during this stress condition because of creation of high osmotic potential, that hinder water absorption (osmotic effect) or produce lethal effects of Na⁺ and Cl^– ions (Okcu et al., 2005).

Early leaf aging is also observed in saline stress condition. Leaf aging means low chlorophyll content or protein and higher rate of cell membrane conductivity. There are also high amount of Na⁺ and Cl^– ions in leaves and low concentration of K⁺ and Ca²⁺ ions (Kusvuran et al., 2007; Chen et al., 1991). It has been reported that saline tolerance differs in cucurbits with variable ranging from sensitive to medium tolerance. Under salt stress condition plants show decline in root, shoot and body length, drop of fresh and dry weight, reduction in leaf area and number, low chlorophyll contents ,low yield with poor quality of fruits (Kusvuran et al., 2007; Greenway et al., 1980). It has been noted that when plants are exposed to salinity for a longer period of time then ion toxicity, deficiency of water and low carbohydrate contents occurs in old as well as in young leaves (Kusvuran et al., 2007; Sivritepe et al., 1999). Under this type of stress, plants are also produced reactive oxygen species. From many researches, it was found that under high level of production of R.O.S. cause cell death (Xia et al., 2009)

Sodium ion having a property to move with in both phloem and xylem of a plant (Kusvuran et al., 2007; Marschner, 1997). Bohra & Doffling, 1993; Kusvuran et al., 2007 examine in their study that ion imbalance condition occur in plants under salt stress; High quantity of sodium ion uptake by plant as compared with other ion resulting in malnutrition. Kusvuran et al., 2007; Levit, 1980 said that when there is high amount of Na ions in growing media then plants uptake sodium higher in amount then requirement. Thus more Na ions are present in plant then potassium or any other ions. Calcium element stands with potassium as it has a vital role in plant strengthen under saline stress condition. Under high salt concentration low intake and transport of calcium in plant takes place (Kusvuran et al., 2007; Cramer et al., 1986). Both Calcium and Potassium are involved in selective transport of ions from cell membrane (Kusvuran et al., 2007; Fageria, 1983).

To control salinity adequate soil drainage is necessary which cause the salts to be leached down. Those crops should be selected which are salt resistant that would helpful in minimizing salinity. Time of watering and application of fertilizer must be proper with respect to the soil situation and growth phase of the crop. Soil analysis also helpful for a superior suggestion of the salt in the soil.  The threshold level above which salt stress causes reduction in growth and productivity vary from crop to crop (Khan et al., 2006). Many researchers have been carried to lessen the drastic effects of salinity. In all of these researches, the use of genetic differences of available germplasm has more valuable because it helps in identification of the genotypes that can be easily adopted to perform well under saline conditions (Ashraf et al., 2006). Screening of genotypes with high salt tolerance and yield potential can strengthen the breeding program. Because of knowing the importance of vegetable family “Cucurbitaceae” and the cruel salinity effects, current research was performed with the intention to screen out cucurbits under saline condition at seedling stage. Tolerant cucurbits genotypes, screened in current investigation can be recommended for cultivation in salt affected areas.