Effect of Synthetic Compounds on Performance of Wheat under High Temperature Stress Condition

Wheat (Triticum aestivum L.) 2n=42 belongs to family Poaceae, mostly cultivated in temperate region as well as in tropical and subtropical climate with moderate success. In India, wheat plays an important role towards food security of the nation. Cultivation of International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 7 Number 05 (2018) Journal homepage: http://www.ijcmas.com

wheat has been the symbol of green revolution and self-sufficiency in food grain production of the nation. According to FAO estimate, world would require around 840 million tonnes of wheat and India require about 140 million tonnes by the year 2050. Environment is continuously changing over the past years due to human-induced activity and extreme climate events. Heat waves, droughts and floods are become a common phenomenon as a result of climate change (IPCC, 2012). Global climate models predict an increase in mean ambient temperatures between 1.8 and 5.8°C by the end of this century (IPCC, 2007). Agricultural production and global food security is directly affected by global warming (Ainsworth and Ort, 2010). Sowing of wheat often gets delayed under rice-wheat cropping system due to late harvesting of paddy (Prasad et al., 2005). Due to late sowing of wheat, anthesis and grain filling period faces increased temperature (more than 20°C) (Tewolde et al., 2006). High temperature stress is a major environmental stress that limits crop growth, metabolism and productivity, because temperature controls the rate of plant metabolic processes that ultimately influence the production of biomass, spikelets and grains (Hay and Walker, 1989). Previous global food assessments have shown that these negative effects are particularly exacerbated in tropical regions (Fischer et al., 2005). Presently, Indian lowlands are the source of approximately 15% of global wheat production but it is anticipated that climate change will transform these into a heat stressed, short season production environment (Bita and Gerats, 2013).Wheat cultivation faces numerous challenges of terminal heat stress, which is a major constraint that limiting the wheat production. High temperature stress during reproductive phase of crop is termed as terminal heat stress. Wheat crop requires 19°C to 22°C temperature during setting and filling of grain (Porter and Gawith, 1999). The threshold temperature i.e. the value of daily mean temperature at which a detectable reduction in growth begins is 26°C for wheat at post anthesis stage (Stone and Nicolas, 1994). During the grain filling period, heat stress can accelerate leaf senescence and affect final grain weight by shortening the duration of grain filling (Dias andLidon, 2009). Lobell et al., (2005) reported that wheat yield in Mexico decreased by 10% for every 1°C increase in night temperature and grain yield showed a strong negative correlation with increasing minimum temperature (Corbellini et al., 1997 andNicolas, 1995). stated that two typical heat stresses are common during wheat grain filling i.e. "Heat shock" which is characterized by sudden extreme high temperatures (>32 0 C) for a short duration (3-5 days) while, "chronic heat stress" consists of moderately high maximum temperatures (20-30 0 C) for a longer duration. High temperature during reproductive phase of wheat resulted, decline in photosynthesis, leaf area, water-use efficiency and decrease shoot and grain mass, kernels weight and sugar content (Shah and Paulsen, 2003). Wheat is much affected by relatively short periods (3-5 days) of heat stress in terms of yields and quality, especially when occurring during grain filling stage (Wardlaw et al., 2002).
The North Indian states such as Uttar Pradesh, Punjab, Haryana, Uttarakhand and Himachal Pradesh are some of the major wheat producing states where the crop is more vulnerable at a 1°C rise in temperature resulting in reduction of wheat yield (Singh et al., 2011) and according to a report of Ministry of Agriculture, GOI, 1 0 C rise temperature during the growing season can result in 3-7% decrease in grain yield. Loss in yield of wheat due to elevated temperature is estimated in the vicinity of 50 percent by 2050 (IFPRI 2011). This yield loss will threaten the food security of at least 1.6 billion people in South Asia.
The yield loss of late sown wheat facing high temperature stress can be improved by exogenous application of many synthetic compounds. These synthetic compounds are inorganic salts like potassium nitrate, calcium chloride, glycine betaine and arginine. Several studied says that these compounds mitigate the ill effects of high temperature stress in plants through various mechanisms like preventing the degradation of chlorophyll, reducing electrolytic leakage and help to maintain or sometime increase the grain yield of crop. The main function of these compounds is as follow; KNO 3 -Potassium (K+) has substantial effect on enzyme activation, protein synthesis, photosynthesis, stomatal movement and water-relation (turgor regulation and osmotic adjustment) in plants (Marschner, 1995). Increased application of K+ has been shown to enhance photosynthetic rate, growth, yield and drought resistance in different crops under abiotic stress conditions (Egilla et al., 2001). CaCl 2 -Under heat stress, Ca 2+ can maintenance of antioxidant activity in some cool season grasses (Jiang and Haung, 2001). Calcium application in the form of CaCl 2 increased the malondialdehyde (MDA) content (lipid per oxidation product) and stimulated the activities of SOD and catalase, which could be the reason for the induction of heat tolerance (kolupaev et al., 2005). Glycinebetaine -Glycinebetaine is the low molecular weight organic compounds have been successfully applied to induce high temperature tolerance in plants.Numerus reports are also available to show beneficial effects of some compounds like potassium nitrate (Sarkar and Bandopadhyay, 1991;Sarkar and Tripathy, 1994), calcium chloride (Tan et al., 2011), glyceinebetaine (Rhodes andHanson, 1993, Ashraf et al., 2007) and arginine (Hassanein et al., 2013) in many crops including wheat when applied exogenously under abiotic stresses like high temperature and drought. The main functions of these sprayed compounds are protection of chlorophyll, detoxification of reactive oxygen species, maintenance of favorable balance of water and photosynthesis in plants under stressful condition.
So, this experiment was conducted to test the efficacy of these synthetic compounds for improving grain yield by enhancing tolerance capacity of the crop against high temperature stress. Our mainfocus is reducing the impact of heat stress during reproductive and grain filling stages of wheat and develop a strategy to improve tolerance in late sown wheat.

Experimental site
A field experiment was conducted during rabi season 2014-15 at Crop Research Farm, Department of Agronomy, Bihar Agricultural University, Bhagalpur, Bihar. The geographical location of Bhagalpur comes under the Middle Gangetic plain region of Agro-climatic Zone III (A) in Bihar. It located between 25 o 50' N latitude and 87 o 19' longitude at an altitude of 52.73 meter above mean sea-level. The soil at the experimental site was sandy loam with pH 6.92, bulk density 1.49 g cm -3 , organic carbon 0.49% and having 125.44, 18.05 and 118.95 kg ha -1 N: P: K respectively.

Climatic conditions of site
Climate of Sabour, Bhagalpur is sub-tropical, hot desiccating summer, cold winter and moderate rainfall. December and January are usually the coldest month where the mean temperature normally fall as low as 8.8 0 C whereas; May and June are the hottest months, having the maximum average temperature of 36.1°C. The average annual rainfall is about 1207 mm (10 years' average) precipitating mostly between middle of June to middle of October.

Weather parameters during the experimental period
During experiment the maximum temperature varied from 18.1-32.2 o C, minimum temperature ranged from 5.8-20.5 o C and mean temperature period varied from 11.95-25.95 o C. So, meteorological data reveals that the wheat crop faced high temperature stress (beyond 20 o C) from February 2 nd week onwards, which coincides with its grain filling stage. The crop received a total rainfall of 9.48 mm from December, 2014 to March 2015.

Experimental details
The experiment was laid out in the split plot design with three replications and size of experimental plot was 10 m 2 . Sowing date was December 29, 2014 which considered as late sown irrigated condition for the region, with spacing 20 cm (row to row) and fertilizer dose was 80: 40: 40: (N: P 2 O 5 : K 2 O Kg/ha). In this experiment two contrasting wheat varieties had been taken namely, DBW-14 (V1) and K-307 (V2). Variety DBW-14 is recommended for late sown irrigated conditions. The optimum sowing time of this variety is between 10 th December to last week of December with 110-115 days' maturity period, having average yielding potential is about 30-40 q ha -1 . Second variety K-307 is recommended for timely sown irrigated condition. The optimum sowing time of this variety is 15 to 30 th November with 125-130 days' maturity period, having average yielding ability is about 40-50 qha -1 . Different chemical compounds are sprayed in different quantity and on different growth stage of wheat for reducing the stress of high temperature. The treatments were; M 1 -control plot, M 2 -KNO 3 at booting stage (1.0%), M 3 -KNO 3 at anthesis stage (1.0%) and M 4 -KNO 3 (0.5%) both at booting and anthesis stage, M 5 -CaCl 2 at booting stage (0.2%), M 6 -CaCl 2 at anthesis stage (0.2%) and M 7 -CaCl 2 (0.1%) both at booting and anthesis stage, M 8 -Gycinebetain at booting stage (100 mM), M 9 -Glycine betain at anthesis stage (100 mM) and M 10 -Glycinebetain (50 mM) both at booting and anthesis stage, M 11 -arginine (2.5 mM) at booting stage, M 12 -arginine atanthesis stage,M 13 -arginine (1.25 mM) both at booting and anthesis stage and M 14 -spray of water at both heading and anthesis stage.

Results and Discussion
Effect of the synthetic compounds on nutrient content and uptake Application of synthetic compounds at different doses and stage does not affected significantly nitrogen and phosphorus (%) content in wheat grain and straw while, potassium content (%) in wheat grain and straw was found to be affected significantly (Table 2). Maximum potassium content (%) was recorded with the application of (M 4 ) KNO 3 @0.5% at booting and anthesis stage in wheat grain (0.29%) and straw (1.28%), followed by KNO 3 @ 1% at anthesis stage in wheat grain (0.28%) and straw (1.26%). Same pattern was observed in nutrient uptake (Table  3) because uptake is totally based on nutrient content and yield of crop. Between varieties there is no significant difference was observed while among treatments K uptake was affected significantly by the application of synthetic compounds. Maximum N uptake (68.66 kg ha -1 ) and P uptake (17.80 kg ha -1 ) was found in variety DBW-14 but maximum K content was recorded variety K-307 (72.67 kg ha -1 ). In case sub plot maximum N uptake (73.48 kg ha -1 ), P uptake (19.28 kg ha -1 ) and K uptake (75.46 kg ha -1 ) was recorded with application of (M 4 ) KNO 3 @ 0.5% at booting and anthesis stage. Application of synthetic compounds provides protection against high temperature stress by several action in plant body. Literature says that these compounds mitigate the ill effects of high temperature stress in plants through various mechanisms like preventing the degradation of chlorophyll, reducing electrolytic leakage from cells etc.
Foliar spray of KNO 3 helps in protecting the photosynthetic apparatus of flag leaf throughout the anthesis and post anthesis period, which is considered to be the principal contributory organ for the supply of photosynthates to the developing grain (Borrill et al., 2015). According to Wahid et al., (2007) photosynthesis is the most sensitive process to elevated temperature and it affects grain yield of wheat (Al-Khatib and Paulsen, 1999). The effect of high temperature during anthesis and grain filling period may disrupt the structure and function of chloroplast and reduces chlorophyll content (Xu et al., 1995), nutrient content and uptake by plants. It has also has been shows that exogenous Ca ++ increased heat tolerance in several plants, which might be associative with high errant oxidative enzyme activities and reduced lipid peroxidation of cell membranes (Wang et al., 2009). The reason behind inclusion of the subplot treatments with glycinebetaine (Agboma et al., 1997) and arginine (Hassanein et al., 2008) is their protective rolesin plants against high temperature stress.

Effect of the synthetic compounds on yields of wheat crop
Grain yield (Table 4) of late sown wheat, facing high temperature stress from anthesis onwards, increased significantly and maximized (34.10 qha -1 ) over control (30.72 q ha -1 ) when the crop was sprayed with 0.5% KNO 3 both at booting and anthesis stage (M 4 ) and was found to be at par with those obtained with M 3 , M 7 and M 6 receiving single foliar spray of 1% KNO 3 at anthesis (33.58 q ha -1 ), two foliar sprays of 0.1% Cacl 2 both at booting and anthesis (33.97q ha -1 ) and a single foliar spray of 0.2% CaCl 2 at anthesis (33.58 q ha -1 ), respectively. Across the two varieties, an increment of 10.99%, 10.59%, 9.45% and 9.31% in grain yield was observed in M 4 , M 7 , M 3 and M 6 , respectively over control.
However, a varietal difference was observed between DBW-14 and K-307 with respect to grain yield when sprayed with different synthetic compounds. The quantum response in grain yield was found to be more pronounced in DBW-14 than in K307.In DBW 14, M 4 treatment produced the highest yield (36.96qha -1 ) which was at par with M 3 (36.52q ha -1 ), M 7 (36.22 q ha -1 ) and M 6 (36.20 qha -1 ) and were 17.28%, 15.88%, 14.93% and 14.88% higher over the yield of M 1 /control (31.51 q ha -1 ), respectively. But in K-307, highest yield was obtained in M 7 (31.73 q ha -1 ) which was followed by M 4 (31.23 q ha -1 ) and were 6.03% and 4.36% higher over the yield ofM 1 /control (29.92 q ha -1 ) respectively.
The maximum straw yield was recorded in variety K-307 (52.75 q ha -1 ) followed by DBW-14 (47.69 qha -1 ) while, by the application of synthetic compounds maximum straw yield was recorded in M 6 (51.61qha -1 ) treatment which was statistically at par with M 4 followed by M 7 and M 3 treatment. The straw yield in M 6 treatment recorded 6.89% increase over M 1 (control) treatment. As the grain and straw yields responded similarly to the foliar spray of synthetic compounds, the harvest index was highest in variety DBW 14 (41.81%). Among the sub plot treatments, M 4 recorded highest harvest index (44.34%) which was 10.95% higher over M 1 (control) treatment followed by M 3 , M 7 and M 6 treatments. On an average, M 4 treatments had the highest HI which was 40.06% higher over M 1 treatment.    Sarkar, 1981;Sakar and Bandopadhyay, 1991). The maximum responsiveness of anthesis stage of wheat towards foliar spray of KNO 3 may be attributed to high sensitivity of this stage against elevated temperature (30/20 0 C, day/night) for 3 days (Saini and Aspinall, 1982). However, if we want to maximize the yield repeated spray at lower concentration is desirable both at booting and anthesis ( Fig. 1 and Table 1).
The simple reason is that repeated spray ensures high insurance against yield loss if staggered spells of high temperature stress occurs during pre-anthesis stage (microsporogenesis) of a crop season which causes poor pollen viability, fewer pollen grains and ultimately leads to lower seed set in cereals like wheat and rice (Prasad et al., 2008). Sakar and Tripathy (1994) also found more or less same trend in case of CaCl 2 whereby repeated spray of low dose CaCl 2 at booting and anthesis gives higher yield however, maximum responsiveness of yield was found when spraying was done at higher concentration during anthesis stage.

Economics of different treatments
The highest gross return was recorded from variety DBW-14 (Rs. 47,960 ha -1 ) which was 14.28% higher over variety K-307(Rs. 41967 ha -1 ). Among subplots, M 4 treatment with the foliar spray of KNO 3 @ 1% at booting stage obtain the highest gross return (Rs. 51,744 ha -1 ) which was 17.28% higher over M 1 (Rs. 43005 ha -1 ) treatment and it was 16.48% higher over M 7 treatment in variety DBW-14. In variety K-307, highest gross return obtained in M 7 treatment (Rs. 44420 ha -1 ) with the foliar spray of CaCl 2 (0.1%) @ both at booting and anthesis stage which is 6.03% higher over M 1 treatment followed by M 4 and M 13 treatments. Over all highest gross return obtained in M 4 treatment (Rs.47733 ha -1 ) which was about 11% higher over M 1 (no spray) treatments followed by M 7 and M 6 treatments.
The net return was highest in variety DBW-14 (Rs. 20328 ha -1 ) which was about 42% higher over the variety K-307 (Rs. 14308 ha -1 ). In sub plot, M 4 treatment obtained the highest net return (Rs. 24439 ha -1 ) which was 33% higher over M 1 treatment followed by M 3 and M 6 respectively. In variety K-307, highest net return obtained in M 14 treatment (Rs.16638 ha -1 ) which was about 3% higher overM 1 treatment.
Overall average net return was obtained in M 4 treatment (Rs.20428 ha -1 ) which was about 18% higher compare to M 1 (no spray) treatment followed by M 3 and M 6 treatments. The B: C ratio was highest in variety DBW-14 (1.75) which was about 14% higher compare to the variety K-307 (1.57). In subplot treatment, M 4 and M 3 obtain the highest B: C ratio (1.90) which was about 11% higher compared to M 1 (no spray).
Overall the highest B: C ratio was recorded in M 4 and M 3 treatment which was about 5% higher compare to M 1 (no spray) treatment. High temperature can affect metabolic process and ultimately reduce the quantity and quality of output. Spray of above compounds provides more yield even in high temperature stress condition and by more yield we get increased returns, which goes loss due to high temperature. Rice-wheat system is predominant system of cropping in Indo-Gangetic regions of Bihar and Uttar Pradesh. Long duration rice varieties take more time to mature and delayed sowing of wheat after rice in this region. Due to late sowing of wheat, reproductive stage of the crop which is considered to be the most sensitive to elevated temperature, coincides with the period of high temperature spells, when mean atmospheric temperature rises beyond 20°C. This imposes stress to the crop during its anthesis to grain filling period. As a result, current photosynthesis gets hampered; resulting in poor translocation of assimilates to the developing grains resulting, lower the yield of wheat.
Based over one-year experimentation, it may be concluded that foliar spray of KNO 3 @ 0.5 per cent followed by CaCl 2 @ 0.1 per cent both at booting and anthesis stage should be applied on short duration wheat variety like-DBW 14for achieving maximum grain yield and economic return under irrigated late sown condition.
These compounds play beneficial role by increasing stomatal movement, protein synthesis, enzyme activation, water balance as well as maintain chlorophyll (photosynthetic ability) in leaves against high temperature loss.