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is ranked third largest country among the edible oil importers. Oil seed
production in Pakistan is about 0.546 million tons that fulfills 27% edible oil
requirement of country and remaining 73% is fulfilled by imports (Economic
survey of Pakistan, 2015-16). Edible oil production in Pakistan is continuously
declining. During the last 20 years, edible oil consumption has been increased
from 0.3 to 2.764 million tons. Pakistan imported 2.205 tons edible oil having
worth US$ 136.920 billion in 2015-16. The total available edible oil from all
sources was 2.667 million tons while domestic production was 0.462 million tons
(Economic survey of Pakistan, 2016). Therefore, difference between supply and
demand is widening increasingly owing to the rapid increase in population (Asif
et al., 2001). This discloses that there is a need to boost up the
production of edible oil in Pakistan by cultivating oilseed crops like

(Hellianthus annuus L.) has wide range of geographical and morphological
diversity and possesses, unique characteristics of tolerance to survive with in
both diverse and adverse climatic conditions, therefore it is regarded as the
crop of broad adaptation (Khalifa et al.,
2000). Pakistan has various ecological zones where sunflower can be cultivated
two times in a year during spring and autumn and has the ability to cope up
with high temperatures (Johnston et al.,
2002). Sunflower has capability to grow in our existing cropping system without
much change in agriculture cropping system on account of its short duration
(Dar et al., 2009).

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Sunflower oil is reputed
as finest quality oil as it consists of soluble vitamins (A, D, E and K) along
with 60% poly-unsaturated fatty acids of which linoleic acid (72%) and oleic
acid (16%) are obsessive that are very helpful in controlling blood cholesterol
level 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 seed
production of 0. 92
million tons and average seed yield of 1.25 t ha-1and oil production
of 35 thousand tons during 2015-16 and it is ranked the third most important
oil seed crop after cotton and rapeseed (Govt. of Pakistan, 2015). Worldwide,
sunflower was cultivated on area of 26.415 million ha with average yield of
1.69 t ha-1 during the same year (NSA, 2016). There is enormous
potential to boost up per acre yield of this precious crop which is being disappeared
due to several reasons.

Abiotic factors play a
vital role in the sunflower yield per acre. Abiotic stress has caused huge
losses in crop yield worldwide (Bray et al., 2000). Among these stresses,the
drought stress is the most significant natural phenomenon which confine plant
growth and productivity (Safarmejad, 2008). Under drought stress, plant growth start
declining or stops (Zhu, 2002).Water stress is a root cause of major reduction
in leaf area index, dry and fresh weight, and plant height of plants (Akinci
and losel, 2010).

abiotic stress, plant cells protect themselves from the stress of high
concentrations of intracellular salts by accumulating different kinds of
organic metabolites that are jointly called as compatible solutes (Ashraf and
Follad 2007). Plants facing unfavorable conditions such as high salt concentrations
decrease their osmotic potential by storing osmolytes that do not interrupt the
functions of enzymes so as to maintain affluent water absorption at the low
soil water potential (Robinson and Jones 1986). The acquisition of these companionable
solutes (osmoprotectants) such as glycinebetaine and, proline facilitate in
maintenance of turgor pressure, stabilization of proteins and membranes against
detrimental effects of abiotic stresses including salinity, drought and
temperature extremes, all of which cause decline in cell water contents (Farooq
et al., 2008b, 2008c). Therefore,
exogenous application of these compounds is another way to genetic engineering
to enhance yield under environmental stress conditions (Heuer 2003). Salicylic acid and related
compounds help in initiation of major effects on different biological process
in plants. These compounds effect in rough manner; hampering certain processes
and boosting others (Raskin, 1992).

Salicylic acid is a general phenolic
compound that is generated in plants and has ability to function as a plant growth
regulator (Arberg, 1981). It play important role in enhancement of the
expression of alternative oxidase enzymes (Rhoads and McIntosh 1992). Salicylic
acid has long been stated as a signal molecule in the commencement of protection
mechanisms in plants (Klessig 2000 and Shah 2003). Salicylic acid has been recognized as a regulatory
signal mediating plant response to several from abiotic stresses such as
drought (Munne-Bosch and Penuelas, 2003; Chini et al., 2004). It plays an important role in abiotic stress
resistance and has ability to induce protective effects on plants under stress
condition (Farooq et al., 2008b). Salicylic acid produces
reactive oxygen species (ROS) in photosynthetic tissues during salt and osmotic
stresses, therefore play essential role in the development of stress symptoms
(Borsani and others 2001).

Foliar application of
fertilizers on crops can be effectual and assure the availability of nutrients
to crops for getting high yields (Arif et
al., 2006). Keeping in view the importance of salicylic acid in life cycle
of plant and its functions under drought stress conditions, a study will be
conducted to explore the potential mitigation role of foliar applied salicylic
acid on field grown sunflower under drought stress conditions.

Review of literature

of drought stress on plant growth and development

According to Nonami (1998) drought affected the physiological
parameters which has ability to effect the growth and development of crop plants.
In plants, cell expansion is suppressed under severe water stress because of interruption
in water movement from xylem to adjacent elongating cells. Water stress suspend
the cell expansion and elongation which badly affects leaf area, plant height
and ultimately the overall crop growth. Drought stress stops assimilate
translocation, photosynthesis, plant water relation and ultimately economic
yield of crop plants (Farooq et al.,
2008). Yield contributing factors such as achene weight, head size and quality
parameters (oil contents) were considerably reduced under severe water stress
condition (Kazi et al., 2002). Human et al. (1998) identified that water
deficit at insemination; flowering and achene filling stages in sun­flower resulted
in severe reduction of achene yield.

The mechanism of cell division, cell
expansion, stem elongation, root proliferation and stomatal oscillation were
undesirably disturbed under water deficit condition which results in less leaf
area, low crop growth rate, less biomass accumulation and eventually caused low
growth, development and yield. Other damaging effects encompass disturbed water
relations, low water use efficiency and plant nutrients and eventually
reduction in crop productivity (Farooq et
al., 2009). Siddique et al.
(2001) also articulated that drought stress declined water potential and leaf
relative water content that resulted in reduction of cell expansion due to low
turgor. Shao et al. (2008) also
determined that plant growth was limited under drought owing to decline in cell
expansion and elongation as a result of low turgor pressure.

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