Pakistanis ranked third largest country among the edible oil importers. Oil seedproduction in Pakistan is about 0.546 million tons that fulfills 27% edible oilrequirement of country and remaining 73% is fulfilled by imports (Economicsurvey of Pakistan, 2015-16).
Edible oil production in Pakistan is continuouslydeclining. During the last 20 years, edible oil consumption has been increasedfrom 0.3 to 2.764 million tons. Pakistan imported 2.
205 tons edible oil havingworth US$ 136.920 billion in 2015-16. The total available edible oil from allsources was 2.
667 million tons while domestic production was 0.462 million tons(Economic survey of Pakistan, 2016). Therefore, difference between supply anddemand is widening increasingly owing to the rapid increase in population (Asifet al., 2001). This discloses that there is a need to boost up theproduction of edible oil in Pakistan by cultivating oilseed crops likesunflower.Sunflower(Hellianthus annuus L.) has wide range of geographical and morphologicaldiversity and possesses, unique characteristics of tolerance to survive with inboth diverse and adverse climatic conditions, therefore it is regarded as thecrop of broad adaptation (Khalifa et al.
,2000). Pakistan has various ecological zones where sunflower can be cultivatedtwo times in a year during spring and autumn and has the ability to cope upwith high temperatures (Johnston et al.,2002). Sunflower has capability to grow in our existing cropping system withoutmuch change in agriculture cropping system on account of its short duration(Dar et al., 2009).Sunflower oil is reputedas finest quality oil as it consists of soluble vitamins (A, D, E and K) alongwith 60% poly-unsaturated fatty acids of which linoleic acid (72%) and oleicacid (16%) are obsessive that are very helpful in controlling blood cholesterollevel and also used in formulation of margarine. Its seeds are of economic value;contain 25-48% oil contents and 20-27% proteins (Hatam and Abbasi, 1994).
Sunflower cake is also used as cattle feed (Satyabrata et al., 1988).Sunflower in Pakistan was cultivated on an area of 0.
214 million ha with seedproduction of 0. 92million tons and average seed yield of 1.25 t ha-1and oil productionof 35 thousand tons during 2015-16 and it is ranked the third most importantoil seed crop after cotton and rapeseed (Govt. of Pakistan, 2015).
Worldwide,sunflower was cultivated on area of 26.415 million ha with average yield of1.69 t ha-1 during the same year (NSA, 2016). There is enormouspotential to boost up per acre yield of this precious crop which is being disappeareddue to several reasons.Abiotic factors play avital role in the sunflower yield per acre. Abiotic stress has caused hugelosses in crop yield worldwide (Bray et al.
, 2000). Among these stresses,thedrought stress is the most significant natural phenomenon which confine plantgrowth and productivity (Safarmejad, 2008). Under drought stress, plant growth startdeclining or stops (Zhu, 2002).Water stress is a root cause of major reductionin leaf area index, dry and fresh weight, and plant height of plants (Akinciand losel, 2010). Underabiotic stress, plant cells protect themselves from the stress of highconcentrations of intracellular salts by accumulating different kinds oforganic metabolites that are jointly called as compatible solutes (Ashraf andFollad 2007). Plants facing unfavorable conditions such as high salt concentrationsdecrease their osmotic potential by storing osmolytes that do not interrupt thefunctions of enzymes so as to maintain affluent water absorption at the lowsoil water potential (Robinson and Jones 1986). The acquisition of these companionablesolutes (osmoprotectants) such as glycinebetaine and, proline facilitate inmaintenance of turgor pressure, stabilization of proteins and membranes againstdetrimental effects of abiotic stresses including salinity, drought andtemperature extremes, all of which cause decline in cell water contents (Farooqet al.
, 2008b, 2008c). Therefore,exogenous application of these compounds is another way to genetic engineeringto enhance yield under environmental stress conditions (Heuer 2003). Salicylic acid and relatedcompounds help in initiation of major effects on different biological processin plants. These compounds effect in rough manner; hampering certain processesand boosting others (Raskin, 1992). Salicylic acid is a general phenoliccompound that is generated in plants and has ability to function as a plant growthregulator (Arberg, 1981). It play important role in enhancement of theexpression of alternative oxidase enzymes (Rhoads and McIntosh 1992).
Salicylicacid has long been stated as a signal molecule in the commencement of protectionmechanisms in plants (Klessig 2000 and Shah 2003). Salicylic acid has been recognized as a regulatorysignal mediating plant response to several from abiotic stresses such asdrought (Munne-Bosch and Penuelas, 2003; Chini et al., 2004). It plays an important role in abiotic stressresistance and has ability to induce protective effects on plants under stresscondition (Farooq et al., 2008b). Salicylic acid producesreactive oxygen species (ROS) in photosynthetic tissues during salt and osmoticstresses, therefore play essential role in the development of stress symptoms(Borsani and others 2001).Foliar application offertilizers on crops can be effectual and assure the availability of nutrientsto crops for getting high yields (Arif etal., 2006).
Keeping in view the importance of salicylic acid in life cycleof plant and its functions under drought stress conditions, a study will beconducted to explore the potential mitigation role of foliar applied salicylicacid on field grown sunflower under drought stress conditions. Review of literatureEffectof drought stress on plant growth and developmentAccording to Nonami (1998) drought affected the physiologicalparameters which has ability to effect the growth and development of crop plants.In plants, cell expansion is suppressed under severe water stress because of interruptionin water movement from xylem to adjacent elongating cells.
Water stress suspendthe cell expansion and elongation which badly affects leaf area, plant heightand ultimately the overall crop growth. Drought stress stops assimilatetranslocation, photosynthesis, plant water relation and ultimately economicyield of crop plants (Farooq et al.,2008). Yield contributing factors such as achene weight, head size and qualityparameters (oil contents) were considerably reduced under severe water stresscondition (Kazi et al., 2002). Human et al. (1998) identified that waterdeficit at insemination; flowering and achene filling stages in sunflower resultedin severe reduction of achene yield.
The mechanism of cell division, cellexpansion, stem elongation, root proliferation and stomatal oscillation wereundesirably disturbed under water deficit condition which results in less leafarea, low crop growth rate, less biomass accumulation and eventually caused lowgrowth, development and yield. Other damaging effects encompass disturbed waterrelations, low water use efficiency and plant nutrients and eventuallyreduction in crop productivity (Farooq etal., 2009). Siddique et al.(2001) also articulated that drought stress declined water potential and leafrelative water content that resulted in reduction of cell expansion due to lowturgor.
Shao et al. (2008) alsodetermined that plant growth was limited under drought owing to decline in cellexpansion and elongation as a result of low turgor pressure.