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Water stress is a severe threat that significantly reduces the crop yield. Exogenous application of salicylic acid play a crucial role in drought resistance. A field trial will be conducted to investigate the effect of foliar application of salicylic acid on achene yield and quality of sunflower (Helianthus annuus L.) under water deficit conditions. Randomized complete block design (RCBD) will be used with split plot arrangement consisting of two factors, factor one is drought stress having three treatments of water (Control-no drought stress, skip irrigation at beginning of stem elongation/40 DAS and skip irrigation at beginning of flowering/70 DAS) and other factor is foliar application of salicylic acid (0mM, 1.5mM of salicylic acid solution at beginning of stem elongation /40 DAS, 1.5mM of salicylic acid solution at beginning of flowering /70 DAS, 1.5mM of salicylic acid solution at beginning of stem elongation/40 DAS and beginning of flowering /70 DAS.) with three replications. Water stress will be induced by skipping irrigation. The net plot size will be 6 × 3m. The crop will be grown during the third week of February using seed at 7.5 kg ha-1. The seeds will be sown on ridges with the help of dibbler.
Need for the Project Pakistan is ranked third largest country among the edible oil importers. Oilseed production in Pakistan is about 0.546 million tons that fulfill 27% edible oil requirement of the country and the 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 of 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, the 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 a sunflower.
Sunflower (Helianthus Annuus L.) has a wide range of geographical and morphological diversity and possesses, unique characteristics of tolerance to survive within 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 the 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).
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 oilseed crop after cotton and rapeseed (Govt. of Pakistan, 2015). Worldwide, sunflower was cultivated on an area of 26.415 million ha with an 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 confines plant growth and productivity (Safarmejad, 2008).
Under drought stress, plant growth starts 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). Under 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 glycine betaine 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 for genetic engineering to enhance yield under environmental stress conditions (Heuer 2003). Salicylic acid and related compounds help in the initiation of major effects on the different biological process in plants. These compounds effect in a rough manner; hampering certain processes and boosting others (Raskin, 1992). Salicylic acid is a general phenolic compound that is generated in plants and his ability to function as a plant growth regulator (Arberg, 1981). It plays important role in the 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 the ability to induce protective effects on plants under stress condition (Farooq et al., 2008b). The salicylic acid produces reactive oxygen species (ROS) in photosynthetic tissues during salt and osmotic stresses, therefore play an 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 the 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. Effect of drought stress on plant growth and development According to Nonami (1998), drought affected the physiological parameters which have the ability to affect 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 suspends 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 sun¬flower 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 a reduction of cell expansion due to low turgor. Shao et al. (2008) also determined that plant growth was limited under drought owing to a decline in cell expansion and elongation as a result of low turgor pressure. Role of salicylic acid in the alleviation of drought stress Rajjou et al., 2006; Alonso-Rami´rez et al., 2009 described that low doses of salicylic acid that are applied exogenously resulted in significantly improved seed germination and seedling establishment of Arabidopsis under different abiotic stress conditions. Under salt stress (100–150 mM NaCl) only 50% of Arabidopsis seeds were germinated, but by the application of salicylic acid @ 0.05–0.5 mM had increased seed germination up to 80%. Exogenous application of salicylic acid also reduced the inhibitory effect of oxidative (0.5 mM parquet) and heat stress (50 C for 3 h) on seed germination (Alonso-Rami´rez et al., 2009). Pancheva et al. (1996) noted that the effects of exogenous application of salicylic acid on photosynthesis parameters were different depending on the dose and plant species tested.
High salicylic acid concentrations (1–5 mM) lowered the photosynthetic rate and RuBisCO activity in barley plants. A lower concentration of salicylic acid (1.0l M) improved the photosynthetic net CO2 assimilation in mustard seedlings. As photosynthetic rate increased, chlorophyll content, carboxylation efficiency and the activities of carbonic anhydrase and nitrate reductase were also up-regulated (Fariduddin et al., 2003). Shakirova et al. (2003) observed that soybean plants treated with 10 nM, and 10 mM, salicylic acid increased the shoot and root growth 20% and 45%, respectively, 7 d after application. Wheat seedlings treated with 50 lM SA develop larger ears, and enhanced cell division is observed within the apical meristem of seedling roots. Khurana and Cleland, (1992) observed that 3–10 lM salicylic acid also stimulated flowering in various genera of the Lemnaceae family, including short day plants, long day plants, and photoperiod-insensitive types.
Exogenously applied 0.5mM salicylic acid ameliorated the drought stress by accumulation of the proline through the increase in ?-glutamyl kinase (GK) and decrease in proline oxidase (PROX) activity. In addition, salicylic acid application inhibited the ethylene formation by restricting the 1-aminocyclopropane carboxylic acid synthase (ACS) activity more conspicuously under moderate drought stress than no stress. It revealed that salicylic acid application alleviated the drought-induced reduction in growth and photosynthesis through increased proline content. (Nazar et al., 2015) Hussain et al. (2008) observed that Glycinebetaine and Salicylic Acid were applied exogenously at 100 and 0.724 mm, respectively, each at the vegetative and at the flowering stage. Drought stress decreased the head diameter, number of achenes, 1000-achene weight, achene yield and oil yield.
Nevertheless, exogenous application of glycinebetaine and Salicylic prominently improved these parameters under water deficit conditions. Wheat seedlings soaked in salicylic acid solution have significantly higher biomass production, leaf number and carbonic anhydrase and nitrate reductase activities than untreated plant seeds (Hayat and others 2005). The application of exogenous salicylic acid improved the survival of pea plants after heat stress. The direct role of salicylic acid synthesis in heat acclimation was proven using inhibitors of salicylic acid synthesis, which reduced not only the endogenous salicylic acid content but also the level of heat tolerance (Pan and others 2006). In cucumber plants (Cucumis Sativa L.), foliar spray with 1 mM salicylic acid-induced heat tolerance, as shown by the lower electrolyte leakage parameter, lower H2O2 and lipid peroxide levels, and higher Fv/Fm chlorophyll a fluorescence value, whereas the hydroponic application of the same concentration had the opposite effect (Shi and others 2006).
Materials and Methods Experimental methods and treatments A field experiment will be conducted at the Agronomy Research Area, the University of Agriculture Faisalabad, during the spring season, 2017 to study the effect of salicylic acid on Sunflower under water stress condition. The experiment will be conducted in Randomized Complete Block Design (RCBD) with split plot arrangement having three replications. The distance between row to row at 75 cm and plant to plant at 20 cm will be maintained. Following treatments will be used for the experiment: Factor 1: Water stress I0 = 4 Irrigations (Full Irrigation) I1 = 3 Irrigations (Skip irrigation at Beginning of stem elongation (40 DAS). I2 = 3 Irrigations (Skip irrigation at Beginning of flowering (70 DAS). Factor 2: Foliar application S0 = Control (simple water treatment) S1 = 1.5mM of Salicylic acid solution at Beginning of stem elongation (40 DAS). S2 =1.5mM of the Salicylic acid solution at Beginning of flowering (70 DAS). S3 =1.5mM of the Salicylic acid solution at Beginning of stem elongation and Beginning of flowering (40 DAS & 70 DAS). Crop husbandry The crop will be sown by maintaining row to row at 75 cm and plant to plant at 20 cm and using a seed rate of 7.5 kg ha-1.
Fertilizer will be applied @ 150 kg N, 100 kg P2O5 ha-1 and 62 kg K2O ha-1. Urea, Diammonium phosphate (DAP) and Murate of potash will be used as sources of fertilizers. Half of the nitrogen, full phosphorus and potash will be applied at sowing and remaining N will be applied with split doses. All other cultural practices such as thinning, weeding, irrigation and plant protection measures will be kept normal.
Following observations will be recorded: Physiological parameters • Leaf water relations (water potential, osmotic potential, and turgor pressure) • Leaf relative water content (%) • No. of stomata per leave. Agronomic parameters Ø Plant height at maturity (cm) Ø Number of plants per plot at harvest Ø Stem diameter (cm) Ø Head diameter (cm) Ø Number of achene per head Ø 1000-achene weight (g) Ø Achene yield (kg ha-1) Ø Biological yield (kg ha-1) Ø Harvest index (%) Quality parameters Ø Achene oil content (%) Statistical analysis The collected data will be analyzed statistically by using Fisher’s analysis of variance technique and treatments means will be compared by using least significant difference test at 5% probability level (Steel et al., 1997).
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