Abstract: A field study was conducted to estimate the effect of salicylic acid (1, 2 and 3 mM), sitosterol as well as putrescine concentrations (0.05, 0.10 and 0.15 mM) on vegetative growth characters, yield and its components and grain biochemical constituents of pearl millet (Pennisetum typhoides (Burm) Stapf. and Hubb) at elongation and milky stages. The application of bioregulators led to significant increases of vegetative growth characters such as plant height, leaf area, leaf area index, dry weight/plant, specific leaf weight, crop growth rate and net assimilation rate except plant height, which significantly reduced with increasing salicylic acid concentration Increasing vegetative character values were obtained at salicylic acid (3 mM), sitosterol or putrescine (0.15 mM) at elongation and milky stages of pearl millet plantsyield and its components, i.e., ear length, ear diameter, grain yield/plant, grain yield/feddan, crop index and 100-grain weight of pearl millet were significantly increased at certain level of applied bioregulators application Salicylic acid (3 mM), sitosterol (0.15 mM) and putrescine (0.15 mM) gave the highest values of the previous yield components. Bioregulators varied of their effect on grain biochemical constituents of pearl millet plant. Sitosterol (0.15 mM) was more effective on crude protein and total carotenoids while putrescine (0.15 mM) was also more effective on total sugars and oil content of grains. Grain yield/feddan showed highly significant and positive correlation with the majority of growth parameters under sitosterol and putrescine application but not with salicylic acid treatments.
Introduction
Salicylic acid is an endogenous growth regulator of phenolic nature, which participates in the regulation of physiological processes in plant, such as stomatal closure, ion uptake, inhibition of ethylene biosynthesis, transpiration and stress tolerance (Khan and Prithiviraj, 2003; Shakirova et al., 2003). The effect of salicylic acid on the physiological processes is variable, promoting some processes and inhibiting others depending on its concentration, plant species, developmental stages and environmental conditions (El-Mergawi and Abdel Wahid, 2004). Low salicylic acid doses enhanced growth of wheat and maize (Shakirova et al., 2003; Shehata et al., 2001).
The diamine putrescine occurred widely in the higher plants. It was suggested to be involved in a variety of growth and developmental processes such as cell division (Bueno and Matilla, 1992), fruit set and growth (Biasi et al., 1991) and senescence (Kao, 1994). The interaction of polyamines with the macromolecules was responsible for physiological effects on plant growth and development (Smith, 1985). Polyamines were effective on inhibiting RNase and protease activities (Kaur-Sawhney and Galston, 1982). Also, Serafmi-Fracassini (1991) found that polyamins are activators of protein process that was related to genes encoding (Imai et al., 2004).
Sitosterol is the major constituent of steroids in plant that plays a critical role in membrane function (Bloch, 1983). Sterols have a main role in plant development Brassinosteroids have been found to evoke both cell elongation and cell division resulting in elongation, swelling, curvature and splitting of the internode (Mandava, 1998). Physiological functions proposed for Brassinosteroids included cell elongation, cell division, leaf bending, vascular differentiation, proton pump-mediated membrane polarization, sink/source regulation responses (Sasse, 1999). In addition, brassinosteroids caused changes in enzymatic activities, membrane potential, DNA, RNA, protein synthesis, photosynthetic activity and changes in the balance of endogenous phytohorornones (Steven and Jenneth, 1998). Particular interest in sterols was elicited by enhanced growth characters and yield of maize and soybean plant (Abdel-Wahed et al., 2000, 2005). Recently, these studies provided strong evidence that sterols could be essential for normal plant growth and development (Ozedemir et al., 2004).
The aim of present research was to study the effect of the three bioregulators (Salicylic acid, sitosterol and putrescine) on growth, yield and some biochemical constituents of pearl millet plants.
Materials and Methods
Grains of pearl millet cultivar (CZI 9623) sown on May 2004 and 2005, respectively at the Gangana village, Jodhpur, Rajasthan. The plot area was 10.5 m2 (3.5x3 m) in rows 60 cm apart and 20 cm apart between hill along the row. The experiments were arranged as a complete randomized block design with six replicates. The plants were sprayed at elongation stage (45 days after sowing) with the following bioregulators: Salicylic acid (C7H6O3) (1, 2 and 3 mM), sitosterol (stigmasta-5-en-β-ol: (24 R)-24 ethylcholest-5-en-3o1) and putrescine (NH4 (CH2)4 NH2) (0.05, 0.10 and 0.15 mM). Control treatment sprayed with distilled water at the same period. Pre-sowing at rate of 100 kg/fed. Calcium superphosphate (15.5% P 205) was applied to the soil. Nitrogen fertilizer as ammonium nitrate (33.5% N) was added at a rate of 120 kg N/feddan in two equal doses the 1st half at 21 and the 2nd at 36 days after sowing.
Growth Characteristics
The following growth characters were measured at elongation stage
(60 days after sowing) and milky stage (90 days after sowing). The vegetative
growth characters were plant height, number of leaves/plant, stem diameter,
dry weight/plant, Leaf area/cm2 according to Bremner and Taha
(1966), leaf area index (Watson, 1952), specific leaf weight (Pearce
et al., 1969), crop growth rate (Abdel-Gawad et al., 1980)
and net assimilation rate (Watson, 1958).
Yield and its Components Characteristics
Yield and its components such as ear length, ear diameter, number
of row/ear, number of grains/row, grain weight/plant, grain yield/fed.,
crop index, 100-grain weight and shelling percentage were determined at
maturity stage.
Chemical Analysis of Grains
Grain samples were dried at 70°C for constant weight and ground
to determine the chemical constituents such as crude protein (Chapman
and Pratt, 1978), total sugars (Dubios et al., 1956), oil percentage
(AOAC, 1988) and total carotenoids (AOAC, 1956).
Statistical Analysis
The data were statistically analyzed in randomized complete block
design according to Snedecor and Cochran (1990) and then combined analysis
as well as simple correlation coefficients between growth characters and
yield attributes were done according to Gomez and Gomez (1984). The treatments
means were compared using LSD test at 5% of significant.
Results and Discussion
Growth Characters
Data presented in Table 1-2 show
that vegetative growth characters of pearl millet such as plant height,
leaf area/plant, stem diameter, leaf area index, dry weight/plant, specific
leaf weight, net assimilation rate and crop growth rate significantly
increased at elongation or milky stages as a result to foliar application
of salicylic acid, sitosterol and putrescine bioregulators. However, number
of leaves/plant was insignificantly affected by bioregulators application.
Plant height significantly decreased with increasing salicylic concentration
up to 3 mM. This mean that salicylic acid might be cause an inhibitory
effect plant elongation, while, sitosterol and putrescine bioregulators
were more effective on all vegetative growth characters. The maximum values
of these characters were obtained by the concentration (3 mM) of all bioregulators
at elongation and milky stages. It appeared from the results that sitosterol
was more effective substance on pearl millet growth than the others. This
effect could be attributed to bioregulators effect on physiological processes
in plant such as, ion uptake, cell elongation, cell division, sink/source
regulation, enzymatic activities, protein synthesis and photosynthetic
activity.
| Table 1: | Effect of some bioregulators on vegetative growth of pearl millet cv. CZI 9623 at elongation stage (60 days after sowing) (Average of two seasons, 2004-2005) |
| Table 2: | Effect of some bioregulators on vegetative growth of pearl millet cv. CZI 9623 at milky stage (90 days after sowing) (Average of two seasons, 2004-2005) |
| Table 3: | Effect of some bioregulators on yield and its component of pearl millet cv. CZI 9623 (Average of two seasons, 2004-2005) |
Present results are in agreement with Shehata et al. (2001) revealed that low salicylic acid doses led to significant increases in growth characters of maize. Similar results were obtained by Khan et al. (2003) on corn and soybean and Shakirova et al. (2003) of wheat. Also, El-Mergawi and Abd El-Wahed (2004) found that the types of plants varied in their response to salicylic acid application as a result to genotype variation. Whereas, steroids have a role on cell elongation, cell division, leaf bending and enzymatic activities of plant (Sasse, 1999; Ozdemir et al., 2004). Consequently, the results of putrescine effect on vegetative growth of pearl millet are similar with those obtained by Abd El-Wahed (2000) on maize, Abd El-Wahed and Gamal El-Din (2005) on chamomile.
Yield and its Components
Data in Table 3 show that yield and its components
such as ear length, ear diameter, 100-grain weight, grain yield/plant,
grain yield/fed and crop index were significantly enhanced with foliar
application of bioregulators (salicylic acid, sitosterol and putrescine)
compared with control. However, number of rows/ear and number of grains/row
had no significant increase by all bioregulators applications. Increasing
yield and its components was related to bioregulators concentration up
to 3 mM except ear length character. It appeared from the results that
salicylic acid was more effective than sitosterol and putrescine application
on ear diameter enhancement. Ear length, 100 grains weight, grain yield/plant
and grain yield/fed, were also more affected by sitosterol than the other
bioregulators. However, sitosterol and putrescine treatments did not show
significant differences in their effect on crop index. The favourable
effects of bioregulators were obtained at concentration of salicylic acid
of 3 mM, sitosterol of 0.15 mM and putrescine of 0.05 mM. It might be
due to bioregulators stimulation of physiological processes that were
reflected on improving vegetative growth that followed by active translocation
of the photosynthesis products from source to sink in pearl millet plant.
The previous studies confirmed the present obtained positive responses
of salicylic acid foliar application on soybean (Gutierrez-Coronado et
al., 1998). In addition, brassinosteroids increased peanut yield (Vardhini
and Seeta, 1998) as well as maize and chamomile yield after foliar or
injection application of both stigmasterol or spermidine (Abdel-Wahed,
2000; Abdel-Wahad and Gamal El-Din, 2004). Whereas, increasing or decreasing
putrescine content controlled pistillate flower and pistillate differentiation
(Lin et al., 2001).
| Table 4: | Effect of some bioregulators on some biochemical constitutes of pearl millet cv. CZI 9623 (Average of two seasons, 2004-2005) |
| Table 5: | A simple correlation between grain yield (ton/fed.) and some growth characters under putrescine application |
| * Significant, ** Highly significant | |
Chemical Constituents
Data in Table 4 indicated that foliar application
of salicylic acid, sitosterol and putrescine bioregulators led to significant
effect on some biochemical constituents of pearl millet seed. Crude protein,
oil and total carotenoids content of pearl millet grain tended to increase
while the total sugars content were decreased with enhancement bioregulators
concentration. The maximum values of biochemical content in pearl millet
seed were obtained by sitosterol treatment (0.15 mM) on crude protein
and total carotenoids by putrescine (0.05 or 0.15 mM) on total sugars
and oil. It appeared from the results that both sitosterol and putrescine
are more effective on seed biochemical contents than salicylic acid. This
effect might be due to these substances on enzymatic activity and translocation
of the metabolites to pearl millet seed. These results are agreement with
those obtained by Vardhini and Seeta (1998) they found that the exogenous
application of brassinosteroids enhanced levels of DNA, RNA, soluble proteins,
various carbohydrate and fat content of peanut seed. Also, Abd El-Wahed
et al. (2000) and Abd El-Wahed (2001) found that stigmasterol or
spermidine application increased the previous mentioned contents of maize
seeds. This might be due to their conjugation with sugars and their effect
on α-amylase. So, putrescine or salicylic application promoted nitrate
reductase activity that was positively correlated with total organic nitrogen
of maize (Shankar et al., 2001). In this current study increasing
carotenoids content may due to convert these substances to pyruvic acid
that led to increase biosynthesis of two general classes of carotenoid
pigments carotene and xanthophylls (Martin-Tanguy, 2001; Raskin, 1992).
Correlation Study
Data in Table 5-7 show that grain
yield (ton/fed.) recorded highly significant and positive correlation
with each of plant height, stem diameter, ear length, grain yield/plant
as well as, shelling percentage.
| Table 6: | A simple correlation between grain yield (ton/fed.) and some growth characters under sitosterol application |
| * Significant, ** Highly significant | |
| Table 7: | A simple correlation between grain yield (ton/fed.) and some growth characters under salicylic application |
Significant and positive correlation of grain yield was obtained with crop index and insignificant and positive correlation with 100-grains weight under sitosterol and putrescine application. On the other hand, grain yield (ton/fed.) showed insignificant and positive correlation with plant height, stem and ear diameter, grain yield/plant as well as, crop index. In addition, insignificant and negative correlation of grain yield with ear length, number of rows/ear, number of grains/ear and 100-grains weight under salicylic acid application are shown in Table 4. It appears that the improvement of growth reflected on increasing grain yield/fed. of pearl millet that showed high significant correlation between grain yield, stem diameter, ear diameter, number of rows fear and grain yield/plant under treating pearl millet with sitosterol and putrescine.
From the above mentioned results, it could be concluded that foliar application of sitosterol at 0.15 mM followed by putrescine at 0.15 mM, then salicylic acid at 3 mM to pearl millet CZI 9623 pioneer plant at elongation stages improved growth, yield and its components as well as, some biochemical constituents of pearl millet plants.