Introduction
In the era of climate change, the growth and
productivity of field crops are being significantly affected the world over.
Field crops specialists are striving hard for getting higher yields from the
existing crop varieties by mitigating the adverse effects of unpredictable
climatic changes using different strategies. One of these strategies is the
exogenous application of different growth promoting chemicals and modes of
application may be seed pretreatment, foliar spray or via rooting media, which
have proven of great significance in enhancing growth and productivity (Farooq et al.
2019; Batool et al. 2019; Rashid et al. 2020).
Cereal crops e.g., wheat (Triticum aestivum L.), rice (Oryza sativa L.), maize (Zea mays L.) and barley (Hordeum vulgare L.) are among the major sources
for meeting the food demands of the world population and have therefore been
extensively studied for enhancing their yields. It has been established that
flag leaf in cereals makes the biggest contribution to grain development (Wahid
and Rasul 2005; Farooq et al. 2014).
It has been reported that it is the capacity rather than duration of flag leaf
photosynthesis, which limits the grain filling in wheat (Tambussi
et al. 2007; Borrill
et al. 2015). In view of this, it is
important to enhance the photosynthetic capacity of the flag leaf to accrue
greater grain growth, and the exogenous application of growth enhancers may
play important role in this respect, but the studies are lacking on this
particular aspect.
During spike development, the ear and grains are green
and perform photosynthesis. Source-sink manipulations and carbon (13C)
isotope discrimination revealed a high contribution of ear (~15–29%) and awn
(~4–14%) photosynthesis to grain filling (~15–20%) in durum wheat genotypes
(Merah and Monneveux 2015). These authors obtained
close correlation of awn (r = 0.96)
and chaff (r = 0.86) 13C
discrimination with that of grain. Although the comparative information is
limited for cereal kernels, it is reported that fruit photosynthesis in many
fruit trees contributes by 20–30% to their own carbon economy at unripe stage
(Wahid and Rasul 2005; Farooq et al.
2014). Jiang et al. (2017) improved
the tomato fruit photosynthesis (through CO2 assimilation and
stomatal conductance) by providing light from underneath the canopy. This
indicates that the photosynthetic capacity of the developing fruit can be
enhanced by improving the gas exchange and photosynthetic pigment attributes.
The exogenous application of growth promoting substances can be an effective
approach in achieving this target.
Calcium (Ca) is an essential element for plants since it
plays multiple roles in different plant phenomena. It acts as secondary
messenger in signaling pathway. It also plays central role in stabilizing
membrane, activate metabolic activities and may activate different enzymes (Arshi et al.
2006). Ca also alleviates concomitant yield reduction under stress conditions
in field crops, and helps increase the ion transportation and protects the
membranes (Renault 2005; Hussain et al.
2016). Ca priming improved germination as well as stand establishment in drought
stressed and salt treated plants (Farooq et
al. 20017; 2019). It improved photosynthesis by improving the thylakoid
structural and functional properties (Hochmal et al. 2015). However, studies
pertaining to improved flag leaf and developing grain attributes in cereal
crops with the exogenous application of Ca at critically important reproductive
stage are too limited and need to be established.
In view of the bulging world populace, there is a stern
need to find out strategies to enhance yield of existing crop verities and
understanding the mechanisms involved therein especially under ever-changing
climatic conditions. Exogenous application of Ca, because of its great
biological roles in plant, could be a realistic option for achieving greater
grain yield under field conditions. The objective of this research was to
determine the role of individual and combined application of seed priming and
foliar spray on flag leaf and grain physiological attributes at the onset of
grain filling (GF) stage in wheat growing at two different locations.
Materials and Methods
General
experimental details
Selection
of locations and meteorological conditions: The experiments were
conducted at University of Agriculture, Faisalabad. Location-I was an open area
in the Old Botanical Garden, with relatively more uniform soil and
meteorological conditions due to higher vegetation cover but minimal trees
shading. Location-II was Botany Research Area adjacent to Youngwala
village, characterized by more open and relatively less uniform soil and
meteorological conditions with no vegetation cover. Soil physicochemical
properties from both locations are given in Table 1, while the prevailing
meteorological conditions during the course of experiment in Faisalabad are
given in Fig. 1. For determination of soil properties,
the soil samples from both the locations were collected at 0–30 cm depth, mixed
well and analyzed for physico-chemical properties
(Moodie et al. 1959).
Table 1: Physico-chemical properties of soil collected from
two locations before sowing the wheat crop
|
Soil characteristics |
Location-I |
Location-II |
|
Color |
Brown |
Brown |
|
Textural class |
Loam |
Clayey loam |
|
ECe (dS/m) |
2.50 |
2.97 |
|
SAR (mmol/L) |
12.82 |
17.52 |
|
pH |
7.10 |
7.53 |
|
Organic matter (%) |
1.25 |
0.85 |
|
Sand (%) |
45.56 |
39.21 |
|
Silt (%) |
31.77 |
26.45 |
|
Clay (%) |
22.58 |
34.26 |
|
Available nitrogen (mg/kg) |
7.35 |
5.46 |
|
Available phosphorus (mg/kg) |
5.33 |
4.96 |
|
Available potassium (mg/kg) |
27.5 |
23.63 |
%201591-1600_files/image002.png)
Fig. 1: Meteorological data during the period of experiment
(Nov 2015 to May 2016) in Faisalabad
Source
of seed, treatments application and crop management: The basic
seed of wheat (Triticum aestivum L. cv. Punjab-11)
was obtained from Wheat Breeder, Ayub Agricultural
Research Institute, Faisalabad to perform a field plot (2 m × 3 m) study at
both the locations. The aim was to investigate the effect of unpriming, and individual and combined effects of water and
Ca (-1.25 MPa CaCl2 solution; an optimized concentration) priming
(for 24 h) and foliar spray in enhancing flag leaf and grain growth attributes.
At both locations, the unprimed and primed seeds were sown in lines (22 cm row-to-row
distance) at the seed rate of 125 kg/ha, on 6 November 2015 and recommended
crop management practices including four irrigations, NPK @ NPK @ 120:114:60
kg/ha were applied while weeds were removed by hand. In total, there were 27
plots for nine treatments at each location. Plants were unsprayed, water
sprayed and Ca sprayed at the onset of GF stage and flag leaf and grain
physiological data were recorded 20 days after the foliar spray. At maturity,
the plants were harvested on 25 May at location-I and on 29 May at location-II.
Crop
measurements
Flag
leaf and developing grain characteristics: The flag leaf characteristics
were determined at 20 days after foliar spray. Area of 10 intact flag leaves
per replicate from each treatment was measured as leaf length × leaf width ×
0.68 (correction factor). The gas exchange attributes including net
photosynthetic rate (Pn),
transpiration rate (E), stomatal
conductance (gs)
and substomatal CO2 level (Ci)
of flag leaf and ambient CO2 levels (Ca) were measured using Infra-red gas analyzer (Model LCA-4, ADC
Ltd., Hoddesdon, Herts, UK). The water
use efficiency was determined as Pn/E ratio. To get
dry weight, the same leaves were clipped, dried in an oven at 70oC
for five days and determined for dry weight. The leaf dry weight/leaf area
ratio was also computed. Dried flag leaf tissue was analyzed for nutrient
contents viz., nitrate-N (NO3‑-N),
phosphate-P (PO43--P), potassium (K+), calcium
(Ca2+) and sulphate-S (SO42--S). Ten leaves
were measured for the photosynthetic pigment contents.
To
determine the characteristics of developing wheat grains, 20
days after foliar spray, the spikelets were separated
from the rachis, glume and lema were removed and
grains were carefully removed. A 0.5 g of the grains was transferred to 80%
aqueous acetone immediately after removal and measured for chlorophyll-a (Chl-a), chlorophyll-b (Chl-b) and carotenoids (Car).
Likewise, 0.5 g of the dried grain was determined for their nutrient contents.
Spike
and grain yield attributes: The spike and grain yield components were determined at
maturity by counting number of spikelets per spike
and number of grains per spike from five spikes per replication, while the awn
length was also measured of these spikes. To determine the 1000 grain weight
and grain yield data, the grains were manually extracted. The straw yield was
taken as above ground dry matter including the husk weight.
The harvest index (HI) was calculated as: (grain yield) ×100/straw yield.
Flag
leaf and grain chemical analysis: All the analyses were performed in triplicate. The
chlorophyll composition in both the plant parts was determined by the method of
Arnon (1949) for chlorophylls, while for carotenoids
estimation the method of Davies (1976) was followed. To accomplish this, 0.1 g
of leaf sample and 0.5 g of the grain sample was extracted in 10 mL of 80%
acetone, filtered, made the volume to 10 mL using 80% acetone and measured the
absorbance of the extract at 663, 645 and 480 nm.
To
determine the nutrient contents of the tissues (except NO3--N),
the dried material was digested in acid mixture (HNO3:HClO4,
3:1 ratio) on a heating block by gradually increasing the temperature to 250oC
until the samples became clear; filtered and made the volume up to 25 mL. K+ and Ca2+ contents were
measured using flame-photometer (Model 410, Sherwood Scientific Ltd., Cambridge, UK). The PO43--P contents
were measured using spectrophotometer with molybdate-vanadate reagent (Yoshida et al. 1976) while SO42--S
content was estimated with the method of Tendon et al. (1993). To
extract NO3--N, the dried flag leaf and grain samples
(0.1 and 0.5 g, respectively) were digested in a mixture of H2SO4
and H2O2 (1:1 ratio) using a heating block, while to
measure NO3--N, the method of Kowalenko
and Lowe (1973) was used.
Statistical
analysis
The design of experiment was completely randomized
factorial with three replications per treatment at both the locations. To find
out the cardinal differences in the parameters investigated above, the data
from each location were statistically analyzed
separately for two-way variance analysis (ANOVA)
to find out the presence or absence of differences and interactions in various
factors using Statistics8.1 software (Table 2). In the absence of any large cardinal differences in
the investigated parameters, the data from location-I were processed
statistically to find significant (P <
0.05) differences in the treatment means by using least significant
difference (LSD) test. Correlations of flag leaf growth attributes with its gas
exchange, photosynthetic pigments and nutrient attributes were established
using Microsoft Excel 2010 release. Similarly, correlation of pigments and
nutrient contents with 1000 grain weight and grain yield per plant were also
established.
Results
Variations between locations
The differences in the
locations were reflected from the ANOVA carried out for data of all the parameters
from both the locations. There were fewer differences in the locations as the interactions
of priming and foliar spray treatment disappeared at location-II for E, Ci, flag leaf and grain NO3--N
and number of grains per spike at location-II but were apparent at location-I. On the contrary, the interactions were
strongly evident for flag leaf dry weight/area ratio, Pn, awn length and HI at
location-I but weaker at location-II (Table 2). Such differences appeared
mainly due to differences in soil properties at both locations (Table 1).
Table 2: Analysis of
variance (F-ratio) of wheat flag leaf
and grain characteristics under seed priming and foliar spray treatments at two
locations in Faisalabad in the year 2015–2016
|
Parameters |
Location-I |
Location-II |
||||
|
|
Seed priming
(SP) |
Foliar spray
(FS) |
SP × FS |
Seed priming
(SP) |
Foliar spray
(FS) |
SP × FS |
|
Flag leaf dry
weight (FLDW) |
22.97** |
96.19** |
3.30* |
18.53** |
65.32** |
4.66* |
|
Flag leaf area
(FLA) |
67.31** |
41.12** |
3.50* |
78.65** |
32.14* |
4.12* |
|
FLDW/FLA |
18.21** |
28.29** |
5.35** |
16.57** |
16.24* |
3.28* |
|
Flag leaf net
photosynthesis (Pn) |
22.84** |
65.02** |
5.24** |
17.86** |
42.39** |
3.27* |
|
Flag leaf
transpiration rate (E) |
6.47** |
33.36** |
1.93* |
3.98* |
48.63** |
1.18ns |
|
Flag leaf Pn/E |
2.12ns |
2.55ns |
0.45ns |
2.25ns |
3.01ns |
0.56ns |
|
Flag leaf stomatal conductance (gs) |
3.91** |
31.00** |
0.18* |
3.28* |
24.58** |
0.58** |
|
Sub-stomatal CO2 level (Ci) |
2.51ns |
4.03* |
1.67* |
1.97ns |
3.22* |
0.67ns |
|
Ci/ambient CO2 ratio |
4.25ns |
3.42* |
0.98ns |
3.36* |
3.80* |
0.53ns |
|
Flag leaf Chl-a |
2.19ns |
11.76** |
0.10ns |
2.82ns |
5.95* |
0.20ns |
|
Flag leaf Chl-b |
12.56** |
11.52** |
5.23* |
17.25** |
8.41* |
3.47* |
|
Flag leaf Chl-a/b
ratio |
1.42ns |
1.05ns |
0.23ns |
1.27ns |
1.46ns |
0.41ns |
|
Flag leaf total Chl |
4.46* |
10.85** |
2.17* |
5.13* |
12.98** |
4.12** |
|
Flag leaf Car |
8.59** |
6.06** |
3.57* |
6.72** |
7.06** |
3.40* |
|
Flag leaf Chl/Car ratio |
3.58* |
3.35* |
0.57ns |
2.98** |
4.25** |
0.29ns |
|
Flag leaf NO3--N
|
29.39** |
6.06** |
2.76* |
18.75** |
9.13** |
1.06ns |
|
Flag leaf PO43--P
|
2.93ns |
5.34** |
1.84ns |
3.25* |
6.08** |
0.79ns |
|
Flag leaf K+ |
2.96* |
2.78* |
0.58ns |
3.87* |
1.68ns |
0.70ns |
|
Flag leaf Ca2+
|
0.87ns |
1.75* |
0.42ns |
0.50ns |
2.10** |
0.36ns |
|
Flag leaf SO42--S
|
6.34** |
5.10* |
2.11* |
9.83** |
3.24* |
1.87* |
|
Grain Chl-a |
10.13** |
36.14** |
3.06* |
6.12* |
42.56** |
2.56* |
|
Grain Chl-b |
2.17ns |
21.22** |
3.06* |
2.92* |
15.14** |
2.21* |
|
Grain Car |
0.58ns |
29.03** |
3.45* |
1.32ns |
8.56* |
2.53* |
|
Grain NO3--N
|
29.39** |
6.06** |
2.96* |
23.87** |
3.25* |
2.01ns |
|
Grain PO43--P
|
17.33** |
3.57* |
1.75* |
9.89** |
5.61** |
1.52* |
|
Grain K+ |
27.15** |
5.89* |
3.10* |
38.57** |
3.45* |
2.78* |
|
Grain Ca2+
|
2.63* |
3.39* |
0.08ns |
3.09* |
2.79ns |
0.13ns |
|
Grain SO42--S
|
1.62ns |
0.64ns |
0.11ns |
1.45ns |
0.81ns |
0.24ns |
|
No. of spikelets per spike |
75.47** |
2.07ns |
0.87ns |
55.20** |
5.07ns |
0.69ns |
|
Awn length |
32.90** |
12.28** |
2.98** |
13.41* |
45.21** |
3.16* |
|
Number of grains per spike |
34.37** |
15.06** |
3.58* |
43.33** |
5.13* |
1.58ns |
|
100 grains weight |
0.25ns |
7.31** |
0.90ns |
0.71ns |
5.43** |
0.56ns |
|
Grain yield per plant |
31.86** |
33.23** |
5.92* |
23.47** |
42.36** |
3.62* |
|
Straw yield per plant |
4.10* |
3.56* |
0.53ns |
2.10ns |
4.56** |
0.29ns |
|
Harvest index |
5.25* |
8.65** |
2.27** |
12.94** |
3.65** |
1.35* |
Degree of freedom;
SP, n = 2; FS, n = 2 and SP × FS, n = 4; Error, 18 and Total, 26
Significant at: *, P
< 0.05; **, P < 0.01 and
ns, P > 0.05
Flag leaf growth and
physiological attributes
Data regarding growth
parameters of wheat revealed that combined application of seed priming and
foliar spray with
Ca most significantly (P < 0.01) improved flag leaf dry weight,
while dry weight/area ratio of flag leaf indicated a more decline at location-I
indicating that the exogenous applications provided more photosynthetic area
than a gain in leaf dry weight (Fig. 2).
For flag leaf gas exchange parameters, data indicated significant (P < 0.01) differences between seed
priming and foliar spray treatments for all parameters while significant (P < 0.05) interaction of these
factors was noted for Pn,
E, gs and Ci. Results showed that Pn, E, Pn/E and gs were the highest while Ci and Ci/Ca were the lowest
with seed priming + foliar spray treatments. The Ca results were followed by
seed priming + foliar spray with water with few exceptions where water
treatments were at par with Ca treatments (Fig. 3).
The flag leaf pigment composition revealed significant differences in
seed priming and foliar spray treatments but interaction
of these factors was evident for Chl-b, total-Chl, and Car. Compared with unprimed + unsprayed
plants, combined Ca priming + foliar spray quite significantly improved the
flag leaf pigments contents especially the Chl-b and Car, thereby declining Chl-a/b
ratio but no specific trend for changes in total-Chl/Car ratios. Water priming + water spray was also effective in
increasing the photosynthetic pigments contents but remained inferior to Ca
treatments, thus suggesting the beneficial role of Ca (Table 3).
The data regarding flag leaf
nutrient content indicated significant differences (P < 0.05) and interactions between seed priming and foliar spray
treatments for flag leaf NO3--N and SO42--S
content, while interaction was noted for PO43--P, K+
and Ca2+ contents. The plants receiving combined Ca priming + foliar
spray treatment exhibited greater nutrient contents in most instances as
compared to those of water primed + foliar sprayed while both these treatments
were superior to untreated plants except the NO3--N contents of unsprayed and Ca primed plants
at par with Ca primed + foliar sprayed plants (Table 4).
%201591-1600_files/image004.png)
Fig. 2: Flag leaf growth characteristics from the wheat grown
from unprimed, water primed and Ca primed seed, and
unsprayed and foliar sprayed with water and calcium solution at grain filling
stage. The columns labeled with letter show significant (P < 0.01) interactions of seed priming and foliar spray
treatments
Correlations data revealed
that flag leaf dry weight and leaf area was positively correlated with all the
photosynthetic pigments contents and gas exchange parameters except no
correlation of flag leaf dry weight with A/E.
On the other hand, none of the flag leaf nutrients was correlated with flag
leaf dry weight while K+, Ca2+ and SO42--S were positively correlated with flag leaf
area. Moreover, flag lead dry weight/flag leaf area was correlated with none of
the photosynthetic pigments, gas exchange and nutrient attributes except NO3--N
contents (Table 5).
Grain physiological attributes
Data regarding developing
grain pigment contents showed significant (P
< 0.01) differences and interactions of seed priming and foliar spray
treatments. Grain Chl-a, Chl-b and Car contents were
noted to be the highest in the plants that received Ca priming + foliar spray
and Ca priming + water spray treatments followed by the grains applied with
water primed + foliar spray treatments. However, unprimed and unsprayed
treatments were at the bottom (Fig. 4).
The grain nutrient data
revealed significant differences in the seed priming and foliar spray
treatments for all the estimated nutrients including NO3--N,
PO43--P, K+, Ca2+ and SO42--S contents while interactions of these factors
was evident for NO3--N, PO43--P
and K+ only. Combined seed priming + foliar spray treatment was the
most effective in enhancing the contents of all nutrients especially NO3--N,
K+ and Ca2+ in the developing grain while Ca priming +
water foliar spray was the second-best treatment in improving the grain
nutrient contents (Table 6). Correlations
of grain Chl-a, Chl-b and Car data were
correlated with none of the nutrient attributes except a positive correlation (r = 0.749; P < 0.05) of grain Chl-a with its Ca
content (data not given).
Yield contributory attributes
Data regarding different grain
yield contributory attributes revealed that there were significant differences
between the seed priming and foliar spray treatments (Table 7), while
interactions of these factors were noted for awn length, number of grains per
spike, grain yield per plant and HI. With no statistical difference, the number
of spikelets per spike was the highest in unsprayed +
Ca primed plants, Ca primed + sprayed treatment and Ca primed + water foliar
sprayed plants. Awn length was the highest in Ca primed + foliar sprayed plants
followed by Ca primed + water sprayed plants and Ca + primed + water sprayed
plants. Number of grains per spike was the highest in Ca primed + foliar spray
treatment followed by Ca sprayed + Water primed and unsprayed + Ca primed
plants while the lowest in unsprayed + unprimed, water sprayed + unprimed and
Ca sprayed + unprimed plants. A 1000 grain weight and grain yield per plant was
the greatest in Ca primed + sprayed plants followed by Ca sprayed + water
primed treatment. Straw yield per plant was the highest in Ca primed + foliar
spray treatment followed by water sprayed + Ca primed and Ca sprayed + water
primed plants. Similarly, highest HI was noted in Ca primed + foliar sprayed
plants followed by Ca foliar sprayed + water primed plants (Table 7). Correlation
data showed that among the various yield components, awn length was positively
correlated with 1000 grain weight (r =
0.693; P < 0.05), grain yield per
plant (r = 0.713; P < 0.05) and HI (r = 0.834; P < 0.01); and also grain yield per plant was positively related
to grain K+ (r = 0.803; P < 0.01), Ca2+ (r = 0.873; P < 0.01) and SO42--S content (r = 0.762; P < 0.05).
%201591-1600_files/image006.png)
Fig. 3: Flag leaf gas exchange parameters of wheat plants grown
from unprimed, water primed and calcium primed seed, and unsprayed or foliar
sprayed with water and calcium solution at grain filling stage. The columns
labeled with letter show significant (P <
0.05) interactions of seed priming and foliar spray treatments
Table 3:
Flag leaf pigment composition of wheat plants grown from unprimed, water primed
and calcium primed seed, and unsprayed or foliar sprayed with water and calcium
solution at grain filling stage
|
Foliar Spray |
Seed Priming |
Concentration
(mg/g fresh weight) |
|||||
|
Chl-a |
Chl-b |
Chl-a/b ratio |
Total Chl |
Car |
Chl/Car ratio |
||
|
Unsprayed |
Unprimed |
2.71±0.14 |
1.08±0.06d |
2.52±0.01 |
3.79±0.20d |
1.21±0.09cd |
3.14±0.21 |
|
|
Water primed |
2.89±0.15 |
1.18±0.05cd |
2.46±0.22 |
4.07±0.12cd |
1.19±0.06d |
3.42±0.09 |
|
|
Calcium primed |
2.83±0.08 |
1.24±0.11bc |
2.29±0.14 |
4.08±0.19cd |
1.34±0.12ab |
3.05±0.13 |
|
Water sprayed |
Unprimed |
2.94±0.14 |
1.14±0.04cd |
2.59±0.15 |
4.08±0.15cd |
1.31±0.06bc |
3.12±0.19 |
|
|
Water primed |
3.10±0.30 |
1.24±0.04bc |
2.50±0.17 |
4.34±0.34bc |
1.30±0.04bcd |
3.34±0.22 |
|
|
Calcium primed |
3.11±0.16 |
1.24±0.06bc |
2.50±0.19 |
4.35±0.16bc |
1.38±0.06ab |
3.15±0.15 |
|
Calcium sprayed |
Unprimed |
3.14±0.28 |
1.22±0.05bc |
2.57±0.24 |
4.37±0.28bc |
1.28±0.05bcd |
3.42±0.16 |
|
|
Water primed |
3.32±0.29 |
1.30±0.06ab |
2.560.23 |
4.63±0.31ab |
1.34±0.06ab |
3.45±0.25 |
|
|
Calcium primed |
3.39±0.20 |
1.38±0.06a |
2.45±0.18 |
4.78±0.20a |
1.43±0.04a |
3.33±0.22 |
Mean
± standard deviation: The means labeled with letter show significant (P < 0.01) seed priming × foliar spray
interactions
Table 4:
Flag leaf nutrient composition of wheat plants grown from unprimed, water
primed and calcium primed seed, and unsprayed or foliar sprayed with water and
calcium solution at grain filling stage
|
Foliar Spray |
Seed Priming |
Concentration
(mg/g dry weight) |
||||
|
|
|
NO3--N |
PO43--P |
K+ |
Ca2+ |
SO42--S |
|
Unsprayed |
Unprimed |
24.67±1.83d |
9.41±0.75 |
31.04±1.57 |
11.97±1.19 |
7.68±0.15c |
|
Water primed |
28.73±2.00b |
9.19±1.09 |
33.23±2.06 |
12.42±0.80 |
7.96±0.75bc |
|
|
Calcium primed |
32.21±2.15a |
9.44±0.07 |
32.42±2.77 |
12.32±1.22 |
9.15±0.71ab |
|
|
Water sprayed |
Unprimed |
24.67±2.26d |
9.74±0.36 |
31.04±2.57 |
11.97±1.19 |
7.35±0.68c |
|
Water primed |
24.53±1.46d |
10.11±0.36 |
32.04±2.34 |
11.92±1.08 |
7.74±0.94c |
|
|
Calcium primed |
28.10±1.45bc |
10.04±0.33 |
33.07±2.81 |
11.91±0.94 |
8.36±0.87abc |
|
|
Calcium sprayed |
Unprimed |
25.41±1.27cd |
9.41±0.75 |
31.04±1.57 |
12.44±1.20 |
7.68±0.15c |
|
Water primed |
25.65±1.99cd |
10.18±0.53 |
34.27±2.28 |
12.74±1.06 |
8.42±0.64abc |
|
|
Calcium primed |
32.93±1.39a |
11.06±0.27 |
36.16±1.98 |
13.68±1.03 |
9.50±0.89a |
|
Mean
± standard deviation: The means labeled with letter show significant (P < 0.01) seed priming × foliar spray
interactions
Table 5:
Correlation coefficient of flag leaf growth characteristics with its pigment
composition, gas exchange and nutrient attributes
|
Variables |
Dry weight |
Leaf area |
FLDW/FLA |
|
Chl-a |
0.972** |
0.833** |
0.271 |
|
Chl-b |
0.855** |
0.970** |
-0.146 |
|
Total-Chl |
0.965** |
0.896** |
0.157ns |
|
Car |
0.731* |
0.769* |
-0.015ns |
|
Pn |
0.924** |
0.920** |
0.055ns |
|
E |
0.949** |
0.791* |
0.296ns |
|
Pn/E |
0.500 |
0.799** |
-0.440ns |
|
gs |
0.870** |
0.712* |
0.300ns |
|
Ci |
-0.949** |
-0.885** |
-0.137ns |
|
NO3--N |
0.154ns |
0.591ns |
-0.691* |
|
PO43--P |
0.264ns |
0.628ns |
-0.589ns |
|
K+ |
0.488ns |
0.816** |
-0.518ns |
|
Ca2+ |
0.582ns |
0.836** |
-0.370ns |
|
SO42--S |
0.416ns |
0.749* |
-0.510ns |
*P < 0.05; **P < 0.01; ns (P > 0.05)
Table 6:
Grain nutrient composition of wheat plants grown from unprimed, water primed
and calcium primed seed, and unsprayed or foliar sprayed with water and calcium
solution at grain filling stage
|
Foliar Spray |
Seed Priming |
Concentration
(mg/g dry weight) |
||||
|
|
|
NO3--N |
PO43--P |
K+ |
Ca2+ |
SO42--S |
|
Unsprayed |
Unprimed |
12.33±0.91d |
4.14±0.16cd |
5.95±0.49d |
2.97±0.21 |
0.43±0.04 |
|
Water primed |
14.36±1.00b |
4.88±0.28ab |
7.70±0.57ab |
3.24±0.26 |
0.47±0.04 |
|
|
Calcium primed |
16.11±1.08a |
4.89±0.22ab |
7.92±0.59a |
3.44±0.20 |
0.49±0.03 |
|
|
Water sprayed |
Unprimed |
12.34±1.13d |
4.00±0.20d |
5.95±0.49d |
2.84±0.17 |
0.43±0.17 |
|
Water primed |
12.27±0.73d |
4.19±0.29cd |
6.83±0.46c |
2.94±0.26 |
0.42±0.11 |
|
|
Calcium primed |
14.05±0.73bc |
4.93±0.10ab |
7.71±0.34ab |
3.34±0.26 |
0.48±0.03 |
|
|
Calcium sprayed |
Unprimed |
12.71±0.63cd |
4.33±0.44cd |
6.95±0.33bc |
3.30±0.23 |
0.45±0.03 |
|
Water primed |
12.82±1.00cd |
4.53±0.38bc |
7.60±0.50abc |
3.64±1.20 |
0.47±0.04 |
|
|
Calcium primed |
16.46±0.69a |
5.02±0.30a |
8.35±0.63a |
3.80±0.15 |
0.52±0.03 |
|
Mean
± standard deviation: The means labeled
with letter show significant (P < 0.01)
seed priming × foliar spray interactions
Table 7: Yield
contributory characteristics of wheat plants grown from unprimed, water primed
and calcium primed seed, and unsprayed or foliar sprayed with water and calcium
solution at grain filling stage
|
Foliar Spray |
Seed Priming |
No. of spikelets per spike |
Awn length (cm) |
No. of grains per spike |
100 grains weight (g) |
Grain yield per plot (kg) |
Straw yield per plot (kg) |
Harvest index (%) |
|
Unsprayed |
Unprimed |
15.33±0.58 |
6.97±0.31ef |
49.33±4.51e |
2.75±0.14 |
2.43±0.19e |
6.84±0.52e |
35.55±1.81de |
|
|
Water primed |
16.67±0.58 |
7.67±0.76cde |
62.33±5.86bc |
2.73±0.14 |
2.81±0.13d |
7.06±0.50d |
39.87±1.18cd |
|
|
Calcium primed |
20.00±1.00 |
7.87±0.38cd |
71.33±6.66ab |
2.73±0.09 |
2.89±0.17d |
7.25±0.38d |
39.90±2.55cd |
|
Water sprayed |
Unprimed |
15.33±0.58 |
6.57±0.31f |
49.33±4.51e |
2.84±0.20 |
2.47±0.23e |
7.04±0.61e |
35.00±1.47e |
|
|
Water primed |
16.00±1.00 |
7.17±0.29def |
59.33±5.86cd |
2.80±0.08 |
3.00±0.13cd |
7.15±0.67cd |
42.10±2.93bc |
|
|
Calcium primed |
19.00±1.00 |
8.93±0.51ab |
71.33±6.66ab |
2.76±0.12 |
3.23±0.11bc |
7.79±0.26bc |
41.54±2.25bc |
|
Calcium sprayed |
Unprimed |
15.33±0.58 |
7.57±0.31cde |
49.33±4.51e |
2.89±0.18 |
2.94±0.22cd |
7.25±0.37cd |
40.72±4.01bc |
|
|
Water primed |
17.33±0.58 |
8.23±0.25bc |
72.67±5.51a |
2.98±0.20 |
3.50±0.23ab |
7.72±0.29ab |
45.41±3.54ab |
|
|
Calcium primed |
19.67±0.58 |
9.63±0.76a |
76.00±4.36a |
3.12±0.15 |
3.80±0.25a |
7.89±0.16a |
48.22±3.79a |
Mean ± standard
deviation.
The means labeled with letter show significant (P < 0.01) seed priming × foliar spray
interactions
%201591-1600_files/image008.png)
Fig. 4: Grain pigment composition of wheat plants grown from
unprimed, water primed and calcium primed seed, and unsprayed or foliar sprayed
with water and calcium solution at grain filling stage. The columns labeled
with letter show significant (P < 0.05)
interactions of seed priming and foliar spray treatments
Discussion
Calcium is a macronutrient and is regarded as central
player in an array of plant biological phenomena (Hapler
2005; Demidchik et
al. 2018). So, its exogenous application has been is of great interest for
crop scientists in improving agronomic traits (Valadkhan
et al. 2015). The results of this
research revealed that both seed priming and foliar spray treatments improved
the flag leaf dry weight and leaf area characteristics, while the ratio of both
these attributes revealed that there was a greater gain in leaf area with the
seed priming and foliar spray treatments of Ca followed by water (Fig. 2). This
implied that exogenous Ca especially at GF stage improved the photosynthetic
area more than the gain in dry weight (Hochmal et al. 2015). The determination of flag
leaf pigment composition, especially Chl-b and Car (Table 3), gas exchange properties,
especially higher Pn
and gs and
quite reduced Ci (Fig. 3), and
greater nutrient content of flag leaf (Table 4) revealed that irrespective of
the application mode, the Ca helped improve the wheat in the field condition.
Furthermore, the presence of close correlations of flag leaf growth attributes
with its pigment contents and gas exchange parameters (Table 5) further
strengthened this standpoint. The exhibition of greater Chl-b and Car content is
important in view of the plants growing in the field since Chl-b is more prone to relative adverse field conditions and Car helps
tolerance against such subversive field conditions (Aderholt et
al. 2017; Hanif and Wahid 2018).
Using 13C
isotope signature, it has been reported that both flag leaf and ear in cereals
are major sources of assimilate partitioning to the grain growth in wheat.
Inherent efficiency of plant genotype to assimilate partitioning from these
parts determines the ultimate grain yield (Sanchez‐Bragado
et al. 2014; Merah and Monneveux 2015). Maintenance of greater grain pigment
composition (Fig. 4) and nutrient content (Table 6) revealed the specific role
of exogenous supply of Ca followed by water priming/spray in the grain filling;
while there was no correlation of grain photosynthetic pigment contents with
nutrient contents (data not shown). This appears to be due to the independent
behavior of biosynthesis of photosynthetic pigments and nutrient partitioning
from ear or flag leaf, but this aspect deserves further investigation.
The data were recorded at
reproductive maturity of crop in order to quantitate the possible role of Ca
and water seed priming/foliar spray treatments in spike and grain yield
components (Table 7). Zoz et al. (2016) reported 9–32% improvement in different spike and
grain yield characteristics with Ca and boron foliar spray. It was specifically
seen in this study that combined application of priming + foliar spray with Ca
followed by water improved awn length, number of grains per spike, grain yield
per plant and HI. It is known that during grain growth, different parts of ear
contribute substantially to grain filling by performing higher rate of
photosynthesis in wheat cultivars (Merah and Monneveux
2015; Wang et al. 2016). It has been
emphasized that awn has a greater contribution to grain filling in cereals due
to showing critically high rate of photosynthesis and respiration (Wahid and
Rasul 2005; Guo and Schnurbusch 2016; Li et al. 2020). Ca seed priming + foliar
spray was quite effective in increasing the awn length mainly by improving awn
photosynthesis (Hochmal et al. 2015) In our study, the awn length was appreciably higher
especially with the foliar spray of Ca (Table 7), which indicated close
associations with grain yield and HI as well. This revealed specific role of
well-elongated awns in contributing its photoassimilates
to grain filling. In addition, grain growth also appeared to be related to
improved grain nutrient contents.
As evident
from results, there were differences in the behavior of wheat especially in the
important attributes such as Pn, E, flag leaf
NO3--N, awn length, number of grains per spike and HI at
the two locations, which are crucial players in the final grain yields (Khaliq et al. 2008; Hochmal
et al. 2015). As given in Table 1,
some of the interactions were strongly evident at location-I but missing at the
location-II or stronger at one location than the other, although treatment
applications and field operations were similar. The only responsible factor for
these changes appears to be more uniform growth conditions at location-I, since
strong genotype × environment interactions are considered quite crucial in the
exhibition of enhanced final grain yield (George and Lundy 2019).
Conclusion
Differences in both the locations were mainly due to
more uniform soil physico-chemical and meteorological
properties at location-I. Flag leaf gas exchange, and pigment composition of flag
leaf and grain were the major determinant of higher grain yield with Ca seed
priming and foliar spray. Awn growth was one of the important spike
characteristics that played a critical role in the ultimate grain yield and HI.
The benefit of seed priming was carried to the reproductive growth stage since
combined priming and foliar spray treatments indicated appreciably greater flag
leaf and grain growth attributes in this field plot study. Further studies on
the time course changes in wheat and possibly other cereals flag leaf and ear
characteristics with Ca foliar spray may improve our understanding of the role
of Ca in improved grain yield.
Author Contributions
NZ and AW planned the study, NZ and KS analyzed data and
interpreted results; TR made illustration and interpreted results. All authors
improved write up.
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