Drought is an Imperative Abiotic-stress that Restricts vegetable Growth and Development
Muhammad Adnan1, Rashad Mukhtar Balal1, Muhammad Adnan Shahid1,3, 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.
Cucurbits are the biggest group of summer vegetables. These are grown in both tropics and subtropics. Cucurbits include melons, cucumbers, pumpkins, gourds and squashes. These have nutritional as well as medicinal value. Generally these have calories, dietry fiber, vitamin A, B, C, D and E, calcium, zinc, iron, magnesium and potassium. These are famous due to their cooling effect on body. Cucurbits work as anti-constipation, lower danger of heart attack and regulate blood circulation (Zhong et al., 2011). Cucumber (cucumus sativus L) is an important vegetable in cucurbitaceae and is native to Asia and Africa. In Pakistan it was grown on area 23268 ha and produced 52766 tonnes yield in year 2016-17 (Government of Pakistan ministry of national food security & research, 2016). It is used as fresh in salad or processed in pickling. Cucumber is vine, have trellise and tendrils, cylindrical fruit (pepo) which may develop by parthenocarpy and leaves develop a canopy on its plant (Huang et al., 2009). It has monoecious habit of flowering, most of them are gynoecious. It contains vitamin B and C along with calcium, iron, magnesium and zinc. It has cooling effect, control jaundice and helps in prevention from constipation (Anonymous, 2012). Cucumber is grown in warm areas of the world and is sensitive to cold. Cucumber has seeded and seedless varieties and can grown in open fields as well as in green house and tunnels for off season crop. Cucumber give better yield on well drained silt loam and sandy loam soils having 5.5-6.7 pH. It need 2.5-3 kg/ha seed for sowing and weekly irrigation (Miano et al., 1991). Melon aphids, melon fruit fly and red pumpkin beetles are worst enemy of cucumber. Diseases like downy mildew and powdery mildew harm its production.
Musk melon (Cucumis melo L.) is member of cucurbitaceae and native to Africa. This has trailing vine growth. Its fruit has aroma. It has less quantity of fat, zero cholesterol, vitamin A, B and C and other important nutrients in its fruit. It gives better yield on loam to clay loam soil. 4-5kg/ha seed is enough for sowing and need 5-6 irrigation to reach maturity (Desai, 2004).
Bottle guard (Lagenaria sicerarta Molina) is a summer crop which belongs to cucurbitaceae and native to Asia and Africa. It is used as vegetable and with meat as a dish. It helps in regulating urine excretion, to reduce weight, to end constipation and is good food for diabetic patients. It require loam to clay loam soil, 4-5 kg/ha seed for sowing and 5-6 irrigations (Erickson et al., 2006). It is also used in making utensils and musical instruments due to its hard core (Chatterjee & Maitra, 2014). Squash (Benincasa fistulosa L.) belongs to cucurbitaceae and is native to India. It is vegetable of warm and dry season.it requires sandy loam to medium loam soil and weekly irrigation for proper growth. Squash helps in preventing from constipation, cancer and overweight. Squash contain Protein 1g , 45 kcal, dietary fiber 2g, Fat 0.1g, Vitamin C 21g, Vitamin 1.44 mg, iron 0.7 mg, Calcium 48mg, zinc 0.15 mg, carbohydrate 11.69 g, Potassium 352 mg and Magnesium 34 mg per 100 gram. (Anonymous, 2017).
Drought is a natural disaster phenomenon and commonly referred to as period without normal or significant rainfall. Circumstances caused by precipitation below the level of plant growth requirement which leads plant into stress. Water shortage can also be defined as the lack of enough moisture, which is indispensable for standard growth of plant and to carry on the life cycle (Zhu, 2002). The major dilemma with drought is that its after-effects appeared very slow, due to which it is particularly known as “creeping phenomena” (Drought bulletin of Pakistan, NDMA, 2015) Pakistan, being an agricultural country has its fame in different horticultural and agronomic crops internationally, has faced severe drought spans in history e.g. 1920 and 1935 in Punjab, 1902 and 1951 in KPK province before independence. The drought of 1998–2002 is deliberated worst and hazardous in past 50 years. Extreme drought durations in years 2000 and 2002 badly affected livelihoods and routine work of lives, caused in human expiries, compelled tens of thousands individuals to migrate from their native areas and killed huge numbers of cattle. This drought ruined 120 deaths and make unexpected destruction of houses of 2,200,000 people (Provancial Disastor Management, 2012). The World Bank apprised that the drought would certainly effect the economic growth of Pakistan (Pakistan Weather Portal).
Currently also facing in many arid areas. In April 2015, precipitation was below -62.35% in Gilgit Baltistan and -27.81% in Baluchistan (Provincial disaster management, 2015). Out of total geographic area of Pakistan 88% falls in the category of arid and semi-arid lands and significantly dependent on revealing rainfall (Mujtaba and Alam, 2002). The foremost arid rangelands are Cholistan Thar, Thal, Tharparkar, Dera Ghazi Khan, Kohistan, and western Baluchistan. History of these areas is worse that belonging to drought circumstances. Hence, 2 to 3 years with in every 10 years in these zones are years of drought (Anonymous, 2015) (www.saarc-sadkn.org) Above conditions are natural timetables. The shortage of suitable moisture has chief role in water stress is usually common incidence in rain fed areas. Pakistan is also facing loss of water in context with irrigation water. Major part i.e. 40% water is lost in seepage and leakage due to irrigation management problems (Anonymous, 2007). Due to diverse effects of global warming the condition of supply of water is very frightening and shocking for whole world (Cook et al., 2007).
Plant reactions to drought in terms of outcomes are of much important because water is life for regularity of plants metabolisms at different stages (Hura et al., 2007).Water stressed plants alter their hormonal equilibrium along with generating ABA in frequent quantity and less amount of cytokinin and gibberellins (Bahrun et al., 2002). Severe circumstances produced by water stress are hazardous for life of plant because of abnormal photosynthesis rate reducing productivity (Yardanove et al., 2003). Due to adverse influences of drought photosynthetic pigments reduced along with reduction of biomass yield (Jaleel et al., 2009). Chlorophyll a and b both quantitatively decreases fallowing the reduction of carotenoids due to less water contents (Farooq et al., 2009). Availability of less water results in complete or partial closeness of stomata, disturbance in regular activity f enzymes. It creates disorder in metabolic functions that are inevitable for normal plant growth (Jaleel et al., 2007). Hostile effects of drought also show retardant in elongation and expansion of cells because of low turgor pressure (Shao et al., 2008). The extreme water stress may show low or restricted photosynthesis and severe disturbance in metabolism that ultimately leads to plant death (Jaleel et al., 2008).
In the face of a mild soil water deficit, plants can maintain photosynthesis and turgor for a short period (Boyer 1970; Morison et al., 2008). However, with unlimited periods of negative soil water potential, plants discontinue growing, show poor photosynthesis and initiate a sequence of events that ensure their survival. Severe drought ultimately re-direct resources to flowering and seed production which disturb the normal growth and yield of crop ( Lawlor and Cornic, 2002; McKay et al., 2003; Morison et al., 2008). Across the range of mild to severe drought circumstances, plants make the most of a range of specific responses to diminish water loss or enlarge the rate of water uptake (Morison et al., 2008). These comprise of continuation of cell turgor and osmotic adjustment , regulation of stomatal conductance (Davies et al., 2002; Buckley 2005) and protection of cellular macromolecules, membranes and enzymes from oxidative damage ( Kranner et al., 2002; Srivalli et al., 2003; Quan et al., 2004).
The reaction and acclimation of plants to soil water scarcity may lead to the action of small molecules or metabolites, together with hormones and protective compounds. Alterations in metabolites in feedback to drought may reveal alterations in photosynthesis (Lawlor and Cornic2002; Villadsen et al., 2005). Negative effects of severe drought induction in plants may lead to the activation of futile cycles to put a stop to over-reduction of photosynthetic electron transport chain (Cornic and Fresneau, 2002; Scheibe, 2004). From roots to shoots chemical signaling through the xylem stream to influence growth, timing of reproduction and stomatal activity are imperative processes influenced by water deficit conditions (Davies et al.,2002; Sharp2002; Morison et al., 2008).