Introduction
Water deficit induced by lack of surface water
availability drastically hampers crop productivity
including of sunflower on irrigated and rainfed fields. Drought is considered
one of the major threats predicted to cause problems for crop production on 50%
of the arable lands across the globe by 2050 (Jensen and Mogenson 1984; Vinocur
and Altman 2005; Cai et al. 2013; Lesk et al. 2016). There are assessments showing that 30–60% water loss
from the total irrigation water applied to soil due to evaporation in the arid
and semi-arid areas (Ashraf 2010). The severity of water stress is further
harnessed by depletion of water from root zone and escalated deficit in
atmospheric vapor pressure may cause reduction in productivity of the crops
ranging from 50 to 73% under water-limited conditions (Davenport et al.
2003; Berry et al. 2013; Ahanger et al. 2014).
Sunflower is one of the most
important oilseed crop, attributed to its high yield potential, wide ranging
adaptability with short growing period. In early seventies, this oil seed crop
was introduced in Pakistan, now it ranks at second position among cash crops.
However, its history of four decades reveals that area and production under
sunflower is declining (Arshad et al.
2010). The area under this crop has been declined to 2, 16,000 hectares with
the total production 109 and 41, 000 tones for seed and oil, respectively (GOP 2016–2017).
The country has an average yield of sunflower 1,060 kg/ha which is far below
than its potential yield of 4,000 kg/ha. Whereas, the history of last three
decades for edible oil reveals that amount of locally produced edible oil is
growing at the rate of 2.56% annually against domestic consumption which is
increasing about 8% annually. Thus, the local production of edible oil from all
available resources could not meet the demand of ever-increasing population.
Rapid expansion in area and increase in domestic oilseed production has become
major challenge for policy makers due to escalating import bill of edible oil.
Sunflower as low to medium
drought sensitive crop is very responsive to environmental conditions such as
soil moisture availability, which adversely affect crop production especially
in semi-arid regions across the globe. It has been investigated that both
magnitude and supply of water could adversely affect achene and oil yield of
sunflower (Krizmanic et al. 2003; Reddy et al. 2003; Iqbal et
al. 2005). Sunflower subjected to water stress at vegetative and
reproductive stage may result in yield reduction of 40 to 61%, respectively
(Iqbal et al. 2004).
The prevailing cropping
systems in rice and cotton zones offer narrow window for sunflower adjustment,
although it is agronomically adapted to agroecological conditions of Pakistan
(Badar et al. 2002). The marginal
lands act as necessary and candidate resource for food production. Use of
marginal lands for cultivation of crops is unavoidable due to reduction in
productive cropped areas mainly in overpopulated areas, on the other hand it is
immensely required to meet increasing demand of food in developing countries
(Laird 1951; Nelson et al. 1997; FAO
2008). Pakistan has total cropped area of 23.76 million hectares. Out of this
79% (18.77 million ha) is irrigated and remaining 21% (4.99 million ha) is
rainfed. The contribution of rainfed area in the total production is one third,
whereas rainfed area has two times less productivity than irrigated area (Baig et al. 2013).
In Pakistan, shortage of water
is one of the limiting factor that leads toward low agricultural productivity.
The availability of water is continuously declining since the time of
independence. Historically,
Pakistan was ranked as water surplus country owning to Indus River system, but
now it is included in the list of water deficit countries. In 1947,
availability of water per capita was about 5000 cubic meters; predicted to
decrease up to 1200 cubic meter per capita by 2025 (Bhatti 1999).
In Pakistan, the demand for water is predicted to grow by a factor of 2.2 by
2050 (Bates et al. 1973). It is obvious that the
country is facing acute shortage of water for use in agriculture. Hence,
strategic planning with concrete measures to properly manage irrigation water
has becomes indispensable (Samdani 2004).
Therefore, one of the emerging interest is to find out
the solutions of water-related problems like drought and its impacts on food
security (Alexanratos and Bruinsma 2012). Especially, it is required to find
out solutions to induce drought tolerance in plants with amelioration of crop
growth to satisfy food demands under limited availability of water resource
(Editorial 2010; Mancosu et al.
2015). Recent studies have elucidated that soil microbes can help crops to
withstand abiotic stresses more effectively. Plant growth-promoting
rhizobacteria (PGPR) have great potential to ameliorate nutritional,
biochemical, physiological and morphological responses of many plants and, thus
confer resistance in plants to alleviate the negative impact of biotic and
abiotic stresses (Marasco et al.
2013). Further, PGPRs are well adapted to hostile environments and may help
plants against damages caused by drought stress, thus ameliorate crop growth
and yield in arid or semiarid regions (Marulanda et al. 2007; Kavamura et al.
2013; Kasim et al. 2013). Drought like
other abiotic stresses induces accelerated ethylene production in plant tissues
which causes abnormal growth in plants (Saleem et al. 2007; Bresson et al.
2013). Inoculation with PGPR having ACC deaminase activity may ameliorate plant
growth by alleviating deleterious effects of ethylene. The rhizosphere
naturally inhabiting the specific PGPR having 1-aminocyclopropane-1-carboxylate
(ACC) deaminase enzyme have the ability to break ethylene precursor ACC, thus
reduce the ethylene level in plants under water stressed conditions (Glick
2004; Nadeem et al. 2013).
Besides PGPRs some chemicals
like glycine betaine, kinetin and salicylic acid are being reported that may
increase yield of different crops by ameliorating the stress induced inhibition
of plant growth (Khan et al. 2003).
Plants exhibit a range of defense mechanisms upon experiencing environmental
stresses that may also be modified artificially or improved by the exogenous
application of chemicals (Raskin 1995; Rajasekaran and Blake 1999). Many commercially
available chemical compounds like salicylic acid, proline, amino acids and
glycine betaine could be applied as promotors to modify status of plant
secondary metabolites and consequently the bioactivity in drought affected
plants.
Salicylic acid act as signal
molecule and plays a vital role in modifying the plant responses to
environmental stresses (Baghizadeh and Rezaei 2011). SA could modulate plant
responses against numerous abiotic stress factors such as drought (Larkindale
and Knight 2002). Several reports revealed that glycine betaine plays an
important role in enhancing of plant tolerance under wide range of abiotic
stresses including of drought (Quan et al.
2004). Accumulation of organic solutes like proline and glycine betaine help
plants for turgor maintenance, strengthening of proteins and membranes to
alleviate negative impact of abiotic stresses including salinity, drought and
temperature extremes that confer cellular water depletion (Farooq et al.
2008a, b). Hence, exogenous application of such chemicals offers an
alternative/additional way to genetic engineering for enhancing of crop yield
under abiotic stresses (Heuer 2003).
Materials and Methods
Experimental material
Experiment
was conducted at the research area of Oil Seed Research Programme, National
Agriculture Research Centre, (NARC) Islamabad (33.69°N, 73.03°E and 470 m. a.
s. l.), Pakistanduring February–June of the years 2016 and 2017 by reproducing
of same layout each year. The type of
experimental soil was sandy clay loam, with pH 7.9, EC 0.35 dS/m, 0.82%
organic matter. Seed of sunflower hybrid
NK-S-278 was obtained from Oil Seed Research Programme, NARC, Islamabad. The
inoculants of ACC deaminase rhizobacteria i.e., KS7 and KS42 were
collected from Soil Microbiology Programme. NARC, Islamabad. While plants were
supplemented with foliar spray of salicylic acid and glycine betaine solutions
at bud initiation (VS) and flower initiation (FS) stages.
Treatments
The present
experiment was laid out in randomized complete block design with split plot
arrangement and was replicated three times by maintaining a net plot size of 7
m x 10 m. Two levels of moisture regimes and various combinations of ACC
deaminase rhizobacteria with SA and GB were the experimental treatments randomized
in the main and sub plots respectively.
Experimental procedure
Prior to
seed bed preparation for planting, field was well presoaked by applying 10 cm
irrigation when soil reached to optimum workable moisture level. Seed bed was
prepared by ploughing with cultivators 2–3 times followed by planking after
each cultivation. The planting was performed with the help of dibbler by
putting two seeds per hill at the rate of 8 kg ha-1. The row to row
distance of 75 cm and plant to plant distance of 25 cm was maintained. After
complete emergence at four leaf stage thinning was performed and one plant per
hill was maintained. Two moisture regimes i.e., M0 = irrigated regime
(no water stress) and M1= rainfed regime (water stress) were maintained. Soil moisture was monitored using Time
Domain Reflectometry (TDR) on weekly basis in both moisture regimes. The water
was applied to irrigation regime in a measured amount with the help of
cut-throat flume by using of formula prescribed by Buland et al. (1994):
QT = AD
In
equation, Q represents discharge rate from flume, T for time, A for area to be
irrigated and D indicates depth of irrigation water applied.
Four irrigations were applied according to crop
requirements in irrigated regime and 300 mm (1=75 mm), while rainfed regime was
not irrigated to maintain two different soil moisture regimes in the field. The
inoculants of ACC deaminase rhizobacteria were used as seed coating. Plants
were supplemented with foliar spray of 0.724 mM salicylic acid and 100 mM
glycine betaine solutions at bud initiation (VS) and flower initiation (FS)
stages, respectively while control treatments received distilled water only. Measured
quantity of salicylic acid was added in beaker containing 200 mL water and
dissolved on magnetic stirrer hot plate at 160oC for 1 h. The
solution was transferred to volumetric flask and 1L volume was made with
distilled water. For glycine betaine, weighted amount of glycine betaine was
added to graduated cylinder and final volume of 1L was prepared in volumetric
flask with distilled water. Recommended doses of fertilizers i.e., 150
kg N ha-1, 100 kg P2O5 ha-1 and 50
kg K ha-1 were applied. Nitrogen was applied in the form of urea and
DAP, phosphorus in the form of DAP while potassium in the form of K2SO4.
Half of the nitrogen, whole phosphorus and potassium were applied at sowing,
while remaining half dose of nitrogen was applied with first irrigation. Weeds
were kept under control by hoeing throughout the life cycle of crop. Plant
protection measures were applied as and when required to keep crop free from
insects and diseases. Chlorpyrefos and Radomil Gold were sprayed to control
whitefly and head rot respectively. The meteorological data for the growth
period of crop during two years 2016 and 2017 was collected from the National
Agro Met Observatory of NARC located near the experimental site. During 2016,
low rainfall of (36.72 mm) and in traces (3.79 mm) was recorded at bud
initiation (VS) and flower initiation stage, respectively. However, in year
2017 low rainfall of (8.35 mm) was recorded at flower initiation (FS).
Plant measurements and statistical analysis
Data regarding
plant water relations, compatible solutes were recorded after 85 days of
sowing. The third leaf from top of the two randomly selected plants from each
treatment was used to determine the leaf water potential (ѱ) with the
help of Scholander pressure chamber by using technique suggested by Scholander et al. (1965). For determination of
osmotic potential, the same leaves were frozen in a freezer at temperature
below -20oC for seven days. After that freezing process leaf
material was thawed and to collect cell sap disposable syringe was used. The
cell sap extracted was used for determination of osmotic potential with the
help of an osmometer (Wescor 5500). Turgor potential was calculated with the
help of following formula by taking the difference of osmotic potential (Ψs) and water potential (Ψw) values.
(Ψp) = (Ψw) - (Ψs)
The leaves
were soaked for 16–18 h to determine turgid weight. Then the same leaves were
kept in oven for 72 h at 65oC until constant dry weight (DW) was
obtained. Relative leaf water content (RLWC) was computed with the help of
following formula proposed by (Schonfeld et al. 1988) and then averaged.
RLWC (%) = (FW-DW)/ (TW-DW)
x100
The ratio between achene yield and water applied was
taken as water use efficiency (WUE).
The leaf free proline from fresh leaf sample was
determined by using protocol mentioned by Bates et al. (1973). The
glycine betaine from dry leaf sample was estimated by using procedure given by
Grieve and Grattan (1983). From the dried leaf samples, total soluble sugars
were extracted and determined by anthrone method of (Riazi et al. 1985) as modified by Ibrahim (1999). Plants were harvested
on June 23, 2016 and June 25, 2017 at harvesting maturity, respectively to
record achene yields. The adjustment in achene yield data was made by
considering of moisture content up to 10% and expressed in kg ha-1.
The data regarding selected traits were subjected to
analysis of variance using software Statistix version 8.1 and means were
compared by Least Significant Differences (LSD) Test at α=0.05.
Results
%20869-881_files/image002.png)
Fig. 1: Effect
of seed bio-invigoration of rhizobacteria combined with exogenous SA and GB
application on water use efficiency (WUE) of sunflower. Different color
bars/lines indicating the effect of various treatments on (WUE)
%20869-881_files/image004.png)
Fig. 2:
Effect of seed bio-invigoration of rhizobacteria combined with exogenous SA and
GB application on achene yield of sunflower. Different color bars/lines
indicating the effect of various treatments on achene yield
Leaf relative water content
Drought stress had negative effects on plant water
relations and water use efficiency, but these parameters were considerably
ameliorated when crop was grown by seed invigoration of ACC deaminase
rhizobacteria and receive exogenous application of SA and GB at vegetative (VS)
and flowering stage (FS) during consecutive years i.e., 2016 and 2017
(Table 1). The results indicated that in case of irrigated regime (M0), more
leaf relative water contents (LRWC) were recorded as compared to rainfed regime
(M1) during both years i.e., 2016 and 2017 (Table 1). Seed inoculation
of rhizobacteria KS7 and KS42 as alone or integrated with salicylic acid and
glycine betaine caused significant difference in LRWC over control. Maximum
LRWC was recorded from treatment C2P2 followed by C2P1, C1P2 and C0P2, which
gave an improvement upto 12, 10, 8, and 7%, respectively over C0P0 (control)
having minimum LRWC during 2017 (Table 1). The interaction between moisture
regimes (M) and various combinations of rhizobacteria i.e. KS7 and KS42
with chemical agents i.e. SA and GB (CP), M x CP, had significant effect
on LRWC during both years i.e. 2016 and 2017 of study (Table 2). During
2016, the maximum LRWC were recorded from M0C2P2 (irrigated regime; seed
inoculation with KS42 and foliar spray of chemicals i.e., GB at VS and
FS stages) followed by M0C2P1, M0C1P2 and M0C0P2 against the minimum in M1C0P0
(rainfed regime; un-inoculated without foliar spray of chemicals i.e.,
SA and GB). However, remaining treatments also caused considerable improvement
in LRWC under varied moisture regimes, but it was statistically at par with
M0C2P0, M0C1P1 and M0C0P1. While, the effect of treatments M0C1P0 & M1C2P2
and M0C0P0 & M1C2P1 was found similar and statistically non-significant. In
year 2017, maximum LRWC was observed in M0C2P2 followed by M0C2P1 and M0C1P2,
but both produced similar and statistically non-significant effect. The rest of
the treatments also caused improvement in LRWC against M1C0P0 which gave
minimum RLWC, but was at par with M1C1P0.
Leaf water and osmotic potential
The results of leaf water and osmotic potential showed
that more leaf water potential and less negative leaf osmotic potential values
were recorded from irrigated regime, whereas more negative values of leaf
osmotic potential and low leaf water potential values were found in case of
rainfed regime (Table 1). Seed invigoration of ACC deaminase rhizobacteria
alone or in supplementation with exogenous application of chemicals i.e.
SA and GB significantly ameliorated leaf water potential and osmotic potential
during both years i.e., 2016 and 2017 (Table 1). In year 2016, maximum
improvement in leaf water potential was observed in C2P2 (where seed
inoculation of KS42 with exogenous application of GB was practiced at bud and
flower initiation stage) followed by C2P1, C1P2 and C0P2, against control C0P0
(un-inoculated and did not receive foliar spray of chemicals. In 2017, same
trend of improvement in leaf water potential was caused by various treatment
combinations as it was observed produced during 2016. The maximum improvement
in leaf water potential and in leaf osmotic potential observed in C2P2 against
minimum in case of control C0P0 (un-inoculated and did not receive foliar spray
of chemicals i.e., SA and GB at bud and flower initiation stage). The
interaction between two factors, M × CP, caused pronounced effect on leaf water
potential during both years i.e., 2016 and 2017 (Table 2). In year 2016,
maximum leaf water potential was recorded from M0C2P2 (irrigated regime; seed
inoculation of KS42 with foliar spray of chemicals i.e., GB at bud and
flower initiation stages) followed by M0C2P1, M0C1P2, M0C0P2 and M0C2P0, which gave statistically at par effect on LRWC. Amongst,
the rest of treatments M0C0P1 and M0C1P1 gave statistically at par results, but
it was similar and statistically non-significant to M0C1P0 under irrigated
regime. The leaf water
potential observed from M0C0P0 under irrigated regime was found statistically
at par with M1C2P1 and M1C2P2 under rainfed regime.
Table 1:
Effect of seed bio-invigoration of rhizobacteria combined with exogenously
applied SA and GB on plant water relations and water use efficiency (WUE) of
sunflower under varied moisture regimes
|
|
RWC (%) |
Water Potential (−MPa) |
Osmotic Potential (−MPa) |
Turgor Pressure (MPa) |
WUE (kg m−3) |
|||||
|
Treatments |
2016 |
2017 |
2016 |
2017 |
2016 |
2017 |
2016 |
2017 |
2016 |
2017 |
|
M0 |
82.17 a |
81.04 a |
0.859
b |
0.916
b |
1.319
b |
1.36
b |
0.46
a |
0.444
a |
0.88 a |
0.84 a |
|
M1 |
74.03 b |
72.85 b |
1.054
a |
1.107
a |
1.447
a |
1.471
a |
0.393
b |
0.364
b |
0.87 b |
0.79 b |
|
LSD (0.05) |
1.091 |
0.888 |
0.052 |
0.064 |
0.049 |
0.044 |
0.028 |
0.022 |
0.011 |
0.027 |
|
C0P0 |
74.17
i |
73.37
g |
1.055
a |
1.08
a |
1.328
h |
1.342
g |
0.273
i |
0.262
g |
0.68
h |
0.64
i |
|
C1P0 |
75.40
h |
73.38
g |
1.01
b |
1.062
ab |
1.362
f |
1.393
f |
0.352
h |
0.332
f |
0.78
g |
0.71
h |
|
C2P0 |
77.93
e |
76.62
e |
0.94
d |
1.012
c |
1.372
e |
1.417
d |
0.432
e |
0.405
e |
0.85
d |
0.79
e |
|
C0P1 |
76.28
g |
74.98
f |
0.982
c |
1.055
b |
1.35
g |
1.395
ef |
0.368
g |
0.34
f |
0.80
f |
0.73
g |
|
C1P1 |
77.30
f |
76.00
e |
0.992
c |
1.012
c |
1.383
d |
1.405
e |
0.392
f |
0.393
e |
0.83
e |
0.76
f |
|
C2P1 |
81.20
b |
80.88
b |
0.89
f |
0.957
e |
1.415
b |
1.44
b |
0.525
b |
0.483
b |
0.98
b |
0.92
b |
|
C0P2 |
79.02
d |
77.68
d |
0.928
de |
0.995
cd |
1.39
cd |
1.425
cd |
0.462
d |
0.43
d |
0.86
d |
0.84
d |
|
C1P2 |
80.03
c |
79.27
c |
0.913
e |
0.985
d |
1.397
c |
1.433
bc |
0.483
c |
0.448
c |
0.94
c |
0.88
c |
|
C2P2 |
82.95
a |
81.82
a |
0.877
f |
0.923
f |
1.427
a |
1.47
a |
0.55
a |
0.547
a |
1.11
a |
1.07
a |
|
LSD (0.05) |
0.535 |
0.876 |
0.017 |
0.018 |
0.014 |
0.010 |
0.013 |
0.012 |
0.016 |
0.014 |
M0 = Irrigated (no water stress), M1 = Rainfed (water
stress), C0P0 = Control (un-inoculated and did not receive foliar spray of
chemicals i.e., SA and GB), C1P0 =
Foliar spray of 0.724 mM SA at bud
initiation (VS) and flowering initiation (FS) stage, C2P0 = Foliar spray of 100
mM GB at VS and FS stage, C0P1 = Seed
inoculation with KS7, C1P1 = Seed inoculation of KS7 with foliar spray of 0.724
mM SA at VS and FS stage, C2P1 = Seed
inoculation of KS7 with foliar spray of 100 mM GB at VS and FS stage, C0P2 = Seed inoculation with KS42, C1P2 =
Seed inoculation of KS42 with foliar spray of 0.724 mM SA at VS and FS stage, C2P2 = Seed inoculation of KS42 with
foliar spray of 100 mM GB at VS and
FS stage, WUE = Water use efficiency, LSD = Least significant difference.
Values sharing same letters in columns are statically non-significant at P = 0.05
Table 2:
Interactive Effect of seed bio-invigoration of rhizobacteria combined with
exogenously applied SA and GB on plant water relations and WUE of sunflower
under varied moisture regimes
|
|
RWC (%) |
Water Potential (−MPa) |
Osmotic Potential (−MPa) |
Turgor Potential (MPa) |
WUE (kg m−3) |
|||||
|
Treatments |
2016 |
2017 |
2016 |
2017 |
2016 |
2017 |
2016 |
2017 |
2016 |
2017 |
|
M0C0P0 |
78.00
hi |
77.03
g |
0.967
e |
0.987
e |
1.283
h |
1.283
h |
0.307
k |
0.297
i |
0.71
l |
0.68
kl |
|
M0C1P0 |
79.30
g |
77.13
g |
0.907
f |
0.953
f |
1.333
g |
1.333
g |
0.38
ghi |
0.38
f |
0.79
jk |
0.74
ij |
|
M0C2P0 |
82.47
e |
81.53de |
0.82
g |
0.91
g |
1.367
e |
1.367
e |
0.493
d |
0.457
d |
0.84
gh |
0.80
gh |
|
M0C0P1 |
80.77
f |
79.80
f |
0.887
fg |
0.947
f |
1.327
g |
1.327
g |
0.39
gh |
0.38
f |
0.80
jk |
0.76
i |
|
M0C1P1 |
81.83
e |
80.90ef |
0.883
fg |
0.89
gh |
1.35
f |
1.35
f |
0.43
ef |
0.46
d |
0.83
hi |
0.79
h |
|
M0C2P1 |
85.20
b |
84.20
b |
0.807
g |
0.867
hi |
1.383
e |
1.383
e |
0.543
a |
0.517
b |
0.97
d |
0.93
c |
|
M0C0P2 |
83.57
d |
82.57cd |
0.807
g |
0.897
g |
1.367
e |
1.367
e |
0.513
bc |
0.47
d |
0.89
f |
0.85
ef |
|
M0C1P2 |
84.33
c |
83.33bc |
0.813
g |
0.89
gh |
1.38
e |
1.38
e |
0.523
bc |
0.49
c |
0.94
e |
0.90
d |
|
M0C2P2 |
86.83
a |
85.87
a |
0.797
g |
0.857
i |
1.407
d |
1.407
d |
0.56
a |
0.55
a |
1.14
a |
1.13
a |
|
M1C0P0 |
70.33
n |
69.70
l |
1.143
a |
1.173
a |
1.383
f |
1.4
de |
0.24
l |
0.227
i |
0.65
m |
0.60
m |
|
M1C1P0 |
71.50
m |
69.63
l |
1.113
b |
1.17
a |
1.437
d |
1.453
c |
0.323
k |
0.283
i |
0.78
k |
0.67
l |
|
M1C2P0 |
73.40
l |
71.70
ij |
1.06
c |
1.113
b |
1.43
de |
1.467
c |
0.37
hi |
0.353
g |
0.87
fg |
0.77
hi |
|
M1C0P1 |
71.80
m |
70.17
kl |
1.077
b |
1.163
ab |
1.423
e |
1.463
c |
0.347
j |
0.3
i |
0.81
ij |
0.70
k |
|
M1C1P1 |
72.77
l |
71.10
jk |
1.1
b |
1.133
b |
1.453
c |
1.46
c |
0.353
ij |
0.327
h |
0.83
hi |
0.73
j |
|
M1C2P1 |
77.20
i |
77.57
g |
0.973
e |
1.047
d |
1.48
b |
1.497
b |
0.507
cd |
0.45
d |
1.00
c |
0.91
cd |
|
M1C0P2 |
74.47
k |
72.80
i |
1.05
c |
1.093
c |
1.46
c |
1.483
b |
0.41
fg |
0.39
ef |
0.83
hi |
0.83
fg |
|
M1C1P2 |
75.73
j |
75.20
h |
1.013
d |
1.08
c |
1.457
c |
1.487
b |
0.443
e |
0.407
e |
0.95
de |
0.87
e |
|
M1C2P2 |
79.07
gh |
77.77
g |
0.957
e |
0.99
e |
1.497
a |
1.533
a |
0.54
ab |
0.543
a |
1.09
b |
1.01
b |
|
LSD (0.05) |
0.756 |
1.238 |
0.024 |
0.026 |
0.012 |
0.015 |
0.019 |
0.018 |
0.023
|
0.021 |
M0 = Irrigated (no water stress), M1 =
Rainfed (water stress), C0P0 = Control (un-inoculated and did not receive
foliar spray of chemicals i.e. SA and GB), C1P0 = Foliar spray of 0.724 mM SA at bud initiation (VS) and
flowering initiation (FS) stage, C2P0 = Foliar spray of 100 mM GB at VS and FS stage, C0P1 = Seed
inoculation with KS7, C1P1 = Seed inoculation of KS7 with foliar spray of 0.724
mM SA at VS and FS stage, C2P1 = Seed
inoculation of KS7 with foliar spray of 100 mM GB at VS and FS stage, C0P2 = Seed inoculation with KS42, C1P2 =
Seed inoculation of KS42 with foliar spray of 0.724 mM SA at VS and FS stage, C2P2 = Seed inoculation of KS42 with
foliar spray of 100 mM GB at VS and
FS stage, WUE = Water use efficiency, LSD = Least significant difference.
Values sharing same letters in columns are statically non-significant at P = 0.05
A minimum leaf potential was recorded from control
M1C0P0 (rainfed regime; un-inoculated and without exogenous application of
chemicals i.e., SA and GB at bud and flowering initiation stage). In
2017, maximum leaf water potential was recorded from M0C2P2 (irrigated regime;
seed inoculation of KS42 with foliar spray of chemicals i.e., GB at bud
and flower initiation stage) followed by M0C2P1, but the effect of both was
found statistically non-significant. The rest of the treatments (M0C1P2 &
M0C1P1; M0C0P2 &M0C2P0 and M0C0P1 & M0C1P0) gave statistically at par
results. While Leaf water potential recorded from M0C0P0 (irrigated regime;
un-inoculated and not receive exogenous application of chemicals i.e.,
SA and GB) and M1C2P2 (rainfed regime; where seed was inoculated with KS42 and
also supplemented with foliar spray of chemicals i.e., GB) were found
statistically at par. The other treatments also produced statistically
significant effect against M1C0P0, which gave minimum leaf potential, but it
was found statistically at par to M1C1P0. The interaction between two factors,
M x CP, gave pronounced effect on leaf osmotic potential during both years i.e.,
2016 and 2017 (Table 2). The results of osmotic potential in response to seed
invigoration of ACC deaminase rhizobacteria with SA and GB foliar spray at VS
and FS stage illustrated that more negative leaf osmotic potential was recorded
from rainfed regime as compared to irrigated regime. In year 2016, the maximum
negative leaf osmotic potential was recorded from M1C2P2 (rainfed regime, seed
inoculation of KS42 with foliar spray of chemicals i.e., GB at bud and
flower initiation stage) followed by M1C2P1, whereas other treatment
combinations M1C0P2, M1C2P2 and M1C1P1 caused produced statistically at par
results of leaf osmotic potential. The effect of M1C1P0 (rainfed regime;
un-inoculated and receive foliar spray of SA) and M0C2P2 (irrigated regime;
seed inoculation of KS42 with foliar spray of GB) was found statistically at
par. Among rest of the treatments M1C0P1, M0C1P2, M0C0P2, M0C2P1 and M0C2P0
gave statistically at par results. The effect of M1C0P0 and M0C1P1 on leaf
osmotic potential was found also statistically at par. The less negative leaf
osmotic potential was recorded from M0C0P0 (irrigated regime; un-inoculated and
did not receive foliar spray of chemicals i.e. SA and GB. In 2017,
maximum negative leaf osmotic potential was caused by M1C2P2 (rainfed regime,
seed inoculation of KS42 with foliar spray of chemicals i.e., GB at bud
and flower initiation stages) followed by M1C2P1, M1C1P2 and M1C0P2, while
their effect was found statistically at par. Amongst, the other treatments
M1C1P1, M1C0P1, M1C2P0 and M1C1P0 produced statistically at par results of leaf
osmotic potential. The rest of treatments M0C1P2, M0C0P2, M0C2P1 and M0C2P0
produced statistically at par results against M0C0P1 and M0C1P1 and M0C0P0
produced minimum negative leaf osmotic potential.
Leaf turgor
potential
Results of leaf turgor potential revealed that varied
moisture regimes caused pronounced effect on turgor potential (Table 1).
Overall, maximum values of leaf turgor potential were resulted from irrigated
regime compared with rainfed regime, which appreciably reduced turgor pressure.
Various treatments of rhizobacteria as alone or integrated with salicylic acid
and glycine betaine caused significant difference in leaf turgor potential over
control (Table 1). In year 2016, the highest value of leaf turgor potential was
caused by C2P2 (seed inoculated with KS42 and foliar spray of chemicals i.e.,
GB at VS and FS) followed by C2P1, C1P2 and C0P2 gave an increment of 101, 92,
77 and 69%, respectively. While minimum leaf turgor potential was recorded from
C0P0 (when crop was grown without inoculation of rhizobacteria i.e., KS7
or KS42 and did not receive exogenous of chemical agents i.e., GB and SA
at VS and FS stage. In 2017, maximum leaf turgor potential was recorded from
C2P2 when seed inoculated with KS42 and foliar spray of chemicals i.e., GB at VS and FS
followed by C2P1, C1P2 and C0P2 gave an increment of 109, 84, 71 and 64%,
respectively over control. Minimum leaf turgor potential was caused by C0P0
(when crop was grown without rhizobacteria inoculation i.e., KS7 or KS42 and
did not receive any foliar spray of chemicals i.e., SA and GB at VS
and FS stage). The interaction between moisture regimes (M) and various
combinations of rhizobacteria i.e., KS7 and KS42 with chemical agents i.e. SA and GB (CP),
M x CP, appreciably affected leaf turgor potential during consecutive years i.e.,
2016 and 2017 (Table 2). In year 2106, the highest value of turgor potential
was recorded from M0C2P2 (irrigated regime; seed inoculation of KS42 with
foliar spray of chemicals i.e., GB at VS and FS) followed by M0C2P1
which caused statistically at par results, but it was similar and
non-significant to M1C2P2 (rainfed regime; seed inoculation of KS42 with
exogenous spay of SA and GB at VS and FS). However, M0C1P2 and M0C0P2 gave
statistically at par results of leaf turgor potential. The rest of treatments
M1C2P1& M0C2P0; M1C1P2 & M0C1P1 also caused significant effect which
were similar and statistically non-significant followed by M1C2P0 and M1C0P2,
while M0C1P0 and M0C0P1 produced statistically non-significant results followed
by M1C1P1 which was similar and non-significant to M1×C0P1. The leaf turgor
potential with M1C1P0 and M0C0P0 was found statistically at par. Minimum leaf
turgor potential was recorded from M1C0P0 (rainfed regime; without
rhizobacteria inoculation and not receive foliar spray of chemicals i.e., chemicals i.e., SA and GB).
In 2017, maximum turgor pressure was recorded from M0×C2P2 (Irrigated regime;
seed inoculation of KS42 with exogenous application of GB) followed by M1C2P2
(rainfed regime; seed inoculation of KS42 with foliar spray of chemicals i.e.,
GB at VS and FS) which were found statistically at par. Amongst, other
treatments M0C2P1 gave significant effect on leaf turgor potential followed by
M0C1P2 which was statistically at par with M0C0P2, M1C2P1and M0C1P1, but it
produced similar results to M1C1P2 which statistically non-significant to
M1C0P2.The treatment combination M0C0P1 and M0C1P0 also produced statistically
at par results. The less increment in leaf turgor potential was recorded from
M1C1P0 and M1C0P1, but both were statistically at par to M1C0P0 (rainfed
regime; without rhizobacteria inoculation and not receive foliar spray of
chemicals i.e., Chemicals i.e., SA and GB at VS and FS which gave
minimum leaf turgor potential.
Water use efficiency
The results of water use efficiency (WUE) illustrated
that maximum water use efficiency was recorded from irrigated regime (M0) as
compared with rainfed regime (M1), which caused a considerable reduction in
water use efficiency during consecutive years i.e., 2016 and 2017 (Table
1). Seed inoculation of rhizobacteria in combination with foliar spray caused
significant differences in WUE during consecutive years i.e., 2016 and
2017 (Table 1). During 2016, maximum WUE was caused by C2P2 (66%) when crop was
grown with seed inoculated KS42 and receive foliar spray of chemicals i.e.,
GB at VS and FS followed by C2P1 (44%), C1P2 (38%) and C0P2 (29%) which gave
statistically at par effect with C2P0. Minimum WUE was recorded from C0P0 when
crop was grown without seed inoculation of rhizobacteria and did not receive
foliar spray of chemicals i.e., SA and GB at VS and FS stage (Fig. 1). In 2017, almost the same trend was
found, where maximum WUE resulted from C2P2 (67%) followed by C2P1 (44%), C1P2
(38%) and C0P2 (31%), while minimum WUE resulted from C0P0 when crop was grown
without seed inoculation of rhizobacteria and did not receive foliar spray of
chemicals i.e., SA and GB at VS and FS stage. The interactive effect
between moisture regimes (M) and various combinations of rhizobacteria i.e.,
KS7 and KS42 with foliar spray of chemicals i.e., SA and GB (CP), M x
CP, on WUE was found significant during consecutive years i.e., 2016 and
2017 (Table 2). During 2016, Maximum WUE was produced by M0C2P2 (irrigated
regime; combination of KS42 with foliar spray of chemicals i.e., GB)
followed by M1C2P2 and M1C2P1 (rainfed regime; combination of KS42 and KS7 with
foliar spray of chemicals i.e., GB). Minimum WUE was caused by M0COP0
(irrigated regime: without seed inoculation of rhizobacteria and did not
receive foliar spray of chemicals i.e., SA and GB at VS and FS).
Amongst, other treatments M0C2P1& M1C1P2 and M0C0P2, M1C2P0 produced
statistically non-significant results, while M0C1P1, M1C1P1 and M1C0P2 caused
statistically at par results. In 2017, the same trend was resulted from various
combinations of rhizobacteria and chemicals as was observed during 2016.
Maximum WUE was produced by M0C2P2 (irrigated regime; combination of KS42 with
foliar spray of chemicals i.e., GB), whereas the minimum WUE was caused
by M0C0P0 (without seed inoculation of rhizobacteria and did not receive foliar
spray of chemicals i.e., SA and GB at VS and FS).
Leaf free proline
The data showed that leaf free proline contents were
significantly affected under varied moisture regimes. Maximum free proline
content were recorded from rainfed regime as compared to irrigated regime
during consecutive years i.e., 2016 and 2017 (Table 3). Seed inoculation
of rhizobacteria in combination with foliar spray of chemicals i.e., SA
and GB at VS and FS stage caused significant effect on free proline content
during consecutive years i.e., 2016 and 2017 (Table 3). During 2016,
maximum free proline content were resulted from C2P2 (57%) when crop was grown
with seed inoculated KS42 and receive foliar spray of chemicals i.e., GB
at VS and FS followed by C2P1 (50%), C1P2 (49%) and C0P2 (40%), respectively
over control. Minimum leaf free proline content were recorded from C0P0 when
crop was grown without seed inoculation of rhizobacteria and did not receive
foliar spray of chemicals i.e., SA and GB at VS and FS. During 2017,
almost the same trend was found, where maximum free proline content resulted
from C2P2 (55%) followed by C2P1 (48%), C1P2 (39%) and C0P2 (38%). While,
minimum free proline content were recorded from C0P0 when crop when crop was
grown without seed inoculation of rhizobacteria and did not receive foliar spray
of chemicals i.e., SA and GB at VS and FS stage. The interactive effect
of moisture regimes (M) and various combinations of rhizobacteria i.e.,
KS7 and KS42 with foliar spray of chemicals i.e., SA and GB (CP), M x
CP, on free proline content was found significant during consecutive years i.e.,
2016 and 2017 (Table 4). During year 2016, Maximum free proline content were
produced by M1C2P2 and M1C2P1 (rainfed regime; combination of KS42 and KS7 with
foliar spray of chemicals i.e., GB and) followed by M1C0P2 and M1C1P2. Contrarily,
the minimum free proline content was caused by M0C0P0 (without seed inoculation
of rhizobacteria and did not receive foliar spray of chemicals i.e., SA
and GB at VS and FS). The rest of the treatments significantly affected leaf free
proline contents, but M0C2P1 and M1C2P0 produced significant results of free
proline content which were statistically at par. In 2017, the same trend was
found, Maximum free proline content were produced by M1C2P2 and M1C2P1 (rainfed
regime; combination of KS42 and KS7 with foliar spray of chemicals i.e.,
GB and), whereas the minimum free proline contents were caused by M0C0P0
(without seed inoculation of rhizobacteria and did not receive foliar spray of
chemicals i.e. SA and GB at VS and FS).
Leaf
glycine betaine
The results of leaf glycine betaine exhibited that more
leaf glycine betaine contents were recorded from rainfed regime as compared
with irrigated regime during consecutive years i.e., 2016 and 2017
(Table 3). The leaf glycine betaine was significantly affected when crop was
grown with inoculation of rhizobacteria and foliar spray of chemicals i.e.,
SA and GB at VS and FS during consecutive years i.e., 2016 and 2017
(Table 3). During 2016, maximum leaf glycine betaine was caused by C2P2 (43%)
when seed inoculated with KS42 and receive foliar spray of chemicals i.e.,
GB at VS and FS, this increase in glycine betaine was more pronounced with C2P1
(35%), C1P2 (25%) and C0P2 (23%) as compared to C0P0 (without seed inoculation
of rhizobacteria i.e., KS7 and KS42 and foliar spray of chemicals i.e.,
SA and GB at VS and FS which produced minimum leaf glycine betaine, although
leaf glycine betaine with C0P1 and C1P1 was found statistically at par. In
2017, the same trend of leaf glycine betaine was caused by various treatment
combinations, maximum leaf glycine betaine was caused by C2P2 (44%) where seed
inoculated with KS42 and receive foliar spray of chemicals i.e., GB at
VS and FS) followed by C2P1 (36%), C1P2 (27%) and C0P2 (25%). However, minimum
leaf glycine betaine was recorded from C0P0
(without seed inoculation of rhizobacteria i.e., KS7 and KS42 and foliar spray
of chemicals i.e. SA and GB at VS and FS). The interaction between varied
moisture regimes (M) and various combinations of rhizobacteria with chemical
agents (CP), M x CP, had significant effect on leaf glycine betaine during consecutive years i.e., 2016 and 2017 (Table 4). During
2016, the results elucidated that maximum leaf glycine betaine was recoded from
M1C2P2 (rainfed regime; seed inoculation of KS42 and foliar spray of chemicals
i.e., GB at VS and FS) followed by M1C2P1,
M1C1P2 and M1C0P2. The minimum leaf glycine
betaine was recorded from M0COP0 (irrigated regime;
un-inoculated and did not receive application of SA and GB at VS and FS). The
rest of the treatments significantly enhanced leaf glycine betaine as compared
to control, but it produced statistically at par results with M1C0P1 and
M1C1P1; M0C0P1 and M1C0P0. In 2017, the same trend of leaf glycine betaine was
found with various treatment combinations of rhizobacteria and chemical agents,
maximum leaf glycine betaine was recoded from M1C2P2 (rainfed regime; seed
inoculation of KS42 and foliar spray of chemicals i.e., GB at VS and
FS). Whereas, minimum leaf glycine betaine was recorded from M0C0P0 (irrigated
regime; un-inoculated and did not receive application of SA and GB at VS and
FS).
Leaf total soluble
sugar
Table 3:
Effect of seed bio-invigoration of rhizobacteria combined with exogenously
applied SA and GB on compatible solutes and achene yield of sunflower under
varied moisture regimes
|
|
Leaf proline content (μmol g─1 f. wt.) |
Leaf glycine betaine (μmol g─1 d. wt.) |
Total soluble sugar (mg g─1
d. wt.) |
Achene yield (kg ha−1) |
||||
|
Treatments |
2016 |
2017 |
2016 |
2017 |
2016 |
2017 |
2016 |
2017 |
|
M0 |
4.33 b |
4.46 a |
11.34
b |
11.47
b |
78.40
b |
78.80
b |
2664
a |
2557
a |
|
M1 |
4.99 a |
5.13 b |
13.24
a |
13.60
a |
84.96
a |
85.61a |
2023
b |
1818
b |
|
LSD (0.05) |
0.226 |
0.130 |
0.314 |
0.364 |
1.360 |
1.486 |
48 |
33 |
|
C0P0 |
3.71
i |
3.69
i |
10.18
h |
10.18
h |
77.38
i |
77.88
i |
1837
h |
1734
h |
|
C1P0 |
4.01
h |
4.02
h |
11.22
g |
11.53
g |
79.48
h |
80.03
h |
2103
g |
1912
g |
|
C2P0 |
4.56
e |
4.70
e |
12.13
e |
12.43
e |
81.50
e |
82.02
e |
2288
e |
2120
e |
|
C0P1 |
4.08
g |
4.14
g |
11.67
f |
11.98
f |
80.10
g |
80.60
g |
2156
fg |
1975
fg |
|
C1P1 |
4.34
f |
4.33
f |
11.73
f |
12.05
f |
80.83
f |
81.35
f |
2220
ef |
2041
f |
|
C2P1 |
5.50
b |
5.67
b |
13.72
b |
13.87
b |
83.98
b |
84.52
b |
2634
b |
2471
b |
|
C0P2 |
5.14
d |
5.23
d |
12.42
d |
12.72
d |
82.12
d |
82.72
d |
2415
d |
2261
d |
|
C1P2 |
5.17
c |
5.36
c |
12.62
c |
12.90
c |
82.92
c |
83.47
c |
2525
c |
2372
c |
|
C2P2 |
5.76
a |
5.85
a |
14.55
a |
14.67
a |
85.53
a |
86.07
a |
2999
a |
2897
a |
|
LSD (0.05) |
0.082 |
0.058 |
0.071 |
0.089 |
0.173 |
0.257 |
73 |
67 |
M0 = Irrigated (no water stress), M1 = Rainfed (water
stress), C0P0 = Control (un-inoculated and did not receive foliar spray of
chemicals i.e., SA and GB), C1P0 =
Foliar spray of 0.724 mM SA at bud
initiation (VS) and flowering initiation (FS) stage, C2P0 = Foliar spray of 100
mM GB at VS and FS stage, C0P1 = Seed
inoculation with KS7, C1P1 = Seed inoculation of KS7 with foliar spray of 0.724
mM SA at VS and FS stage, C2P1 = Seed
inoculation of KS7 with foliar spray of 100 mM GB at VS and FS stage, C0P2 = Seed inoculation with KS42, C1P2 =
Seed inoculation of KS42 with foliar spray of 0.724 mM SA at VS and FS stage, C2P2 = Seed inoculation of KS42 with
foliar spray of 100 mM GB at VS and
FS stage, WUE = Water use efficiency, LSD = Least significant difference.
Values sharing same letters in columns are statically non-significant at P = 0.05
Table 4: Interactive
Effect of seed bio-invigoration of rhizobacteria combined with exogenously
applied SA and GB on compatible solutes and achene yield of sunflower under
varied moisture regimes
|
|
Leaf proline content (μmol g-1 f. wt.) |
Leaf glycine betaine (μmol g-1 d. wt.) |
Total soluble sugar (mg g-1 d. wt.) |
Achene yield (Kg ha−1) |
||||
|
Treatments |
2016 |
2017 |
2016 |
2017 |
2016 |
2017 |
2016 |
2017 |
|
M0COP0 |
3.50
n |
3.47
m |
9.90
o |
9.83
o |
73.33
q |
73.70
q |
2183
g |
2095
gh |
|
M0C1P0 |
3.69
lm |
3.71
m |
10.33
n |
10.47
n |
76.37
p |
76.80
p |
2403
f |
2274
f |
|
M0C2P0 |
3.99
jk |
4.23
j |
11.17
k |
11.27
k |
78.33
m |
78.80
m |
2578
d |
2456
d |
|
M0C0P1 |
3.86
m |
3.88
l |
10.53
m |
10.70
m |
76.83
o |
77.23
o |
2446
ef |
2332
ef |
|
M0C1P1 |
3.93
k |
3.94
k |
10.67
l |
10.83
l |
77.77
n |
78.17
n |
2527
de |
2405
de |
|
M0C2P1 |
5.00
f |
5.20
f |
12.23
g |
12.40
h |
80.17
j |
80.60
j |
2952
b |
2831
b |
|
M0C0P2 |
4.67
hi |
4.86
h |
11.53
j |
11.67
j |
79.13
l |
79.57
l |
2713
c |
2612
c |
|
M0C1P2 |
4.80
g |
5.01
g |
11.73
i |
11.83
i |
79.67
k |
80.07
k |
28657
b |
2747
b |
|
M0C2P2 |
5.21
e |
5.42
e |
13.17
e |
13.30
f |
81.47
i |
81.87
i |
3478
a |
3456
a |
|
M1COP0 |
3.92
kl |
3.90
kl |
10.47
m |
10.53
n |
81.43
i |
82.07
i |
1490
l |
1374
m |
|
M1C1P0 |
4.21
j |
4.33
j |
12.10
h |
12.60
g |
82.60
h |
83.27
h |
1804
jk |
1550
l |
|
M1C2P0 |
5.13
f |
5.16
fg |
13.10
e |
13.60
e |
84.67
e |
85.23
e |
1997
h |
1783
j |
|
M1C0P1 |
4.52
i |
4.53
i |
12.80
f |
13.27
f |
83.37
g |
83.97
g |
1865
j |
1618
kl |
|
M1C1P1 |
4.55
gh |
4.72
h |
12.80
f |
13.27
f |
83.90
f |
84.53
f |
1913
hi |
1677
jk |
|
M1C2P1 |
5.78
b |
5.98
b |
15.20
b |
15.33
b |
87.80
b |
88.43
b |
2316
fg |
2111
g |
|
M1C0P2 |
5.38
d |
5.60
d |
13.30
d |
13.77
d |
85.10
d |
85.87
d |
2118
g |
1911
i |
|
M1C1P2 |
5.28
c |
5.71
c |
13.50
c |
13.97
c |
86.17
c |
86.87
c |
2184
g |
1997
hi |
|
M1C2P2 |
6.30
a |
6.28
a |
15.93
a |
16.03
a |
89.60
a |
90.27
a |
2520
def |
2336
def |
|
LSD (0.05) |
0.116 |
0.082 |
0.101 |
0.126 |
0.244 |
0.363 |
117 |
107 |
M0 =
Irrigated (no water stress), M1 = Rainfed (water stress), C0P0 = Control
(un-inoculated and did not receive foliar spray of chemicals i.e., SA and GB), C1P0 = Foliar spray of
0.724 mM SA at bud initiation (VS)
and flowering initiation (FS) stage, C2P0 = Foliar spray of 100 mM GB at VS and FS stage, C0P1 = Seed
inoculation with KS7, C1P1 = Seed inoculation of KS7 with foliar spray of 0.724
mM SA at VS and FS stage, C2P1 = Seed
inoculation of KS7 with foliar spray of 100 mM GB at VS and FS stage, C0P2 = Seed inoculation with KS42, C1P2 =
Seed inoculation of KS42 with foliar spray of 0.724 mM SA at VS and FS stage, C2P2 = Seed inoculation of KS42 with
foliar spray of 100 mM GB at VS and
FS stage, WUE = Water use efficiency, LSD = Least significant difference.
Values sharing same letters in columns are statically non-significant at P = 0.05
The results of total soluble sugar in response to varied
moisture regimes illustrated that higher total soluble sugar was recorded from
rainfed regime as compared with irrigated regime during consecutive years i.e.
2016 and 2017 (Table 3). The total soluble sugar was considerably affected when
crop was grown with inoculation of rhizobacteria and foliar spray of chemicals i.e.,
GB and SA at VS and FS during consecutive years i.e., 2016 and 2017
(Table 3). During 2016, maximum total soluble sugar was resulted from C2P2
(11%) when seed inoculated with KS42 and receive foliar spray of chemicals i.e.,
GB at VS and FS), this increase in total soluble sugar was more prominent with
C2P1 (8%), C1P2 (7%) and C0P2 (6%) as compared to C0P0 (without seed
inoculation of rhizobacteria i.e., KS7 and KS42 and foliar spray of
chemicals i.e., GB and SA at VS and FS) which produced minimum total
soluble sugar. In 2017, the same trend of total soluble sugar was caused by
various treatment combinations, maximum total soluble sugar was caused by C2P2
(11%) when seed inoculated with KS42 and receive foliar spray of chemicals i.e.,
GB at VS and FS) followed by C2P1 (9%), C1P2 (7%) and C0P2 (6%), whereas,
minimum total soluble sugar was recorded from C0P0 (without seed inoculation of
rhizobacteria i.e., KS7 and KS42 and foliar spray of chemicals i.e.,
SA and GB at VS and FS). The interaction between varied moisture regimes (M)
and various combinations of rhizobacteria with chemical agents (CP), M x CP,
had significant effect on total soluble sugar during consecutive years i.e.,
2016 and 2017 (Table 4). During 2016, the results indicated that maximum total
soluble sugar was recoded from M1C2P2 (rainfed regime; seed inoculation of KS42
and foliar spray of chemicals i.e., GB at VS and FS) followed by M1C2P1,
M1C1P2 and M1C0P2. The minimum total soluble sugar was recorded from M0COP0
(irrigated regime; un-inoculated and did not receive application of SA and GB
at VS and FS). The rest of the treatments significantly enhanced total soluble
sugar as compared to control, but it produced statistically at par results with
M0C2P2 and M1C0P0. In 2017, the same trend of total soluble sugar was found
with various treatment combinations of rhizobacteria and chemical agents,
maximum total soluble sugar was recoded from M1C2P2 (rainfed regime; seed
inoculation of KS42 and foliar spray of chemicals i.e., GB at VS and
FS). Whereas, minimum total soluble sugar was recorded from M0C0P0 (irrigated
regime; un-inoculated and did not receive application of SA and GB at VS and
FS).
Achene yield
The data of achene yield in response to varied moisture
regimes are represented in (Table 3). The results revealed that high achene
yield was recorded from irrigated regime as compared with rainfed regime which
caused a significant reduction in grain yield during consecutive years i.e.,
2016 and 2017. Various combinations of rhizobacteria with chemical agents
caused significant differences in achene yield as indicated in (Table 3). The
achene yield was appreciably affected with inoculation of rhizobacteria and
foliar spray of chemicals i.e., SA and GB at VS and FS during
consecutive years i.e., 2016 and 2017. During 2016, maximum achene yield
was recorded from C2P2 (65%) seed inoculated with KS42 and receive foliar spray
of chemicals i.e., GB at VS and FS), the increase in achene yield was
also prominent with other treatments C2P1 (43%), C1P2 (37%) and C0P2 (31%) as
compared to C0P0 (without seed inoculation of rhizobacteria i.e., KS7
and KS42 and foliar spray of chemicals i.e., SA and GB at VS and FS), which caused minimum achene yield (Fig. 2).
The effect of C1P0 and C0P1; C2P0 and C1P1 on achene yield was statistically
similar and non-significant. In 2017, the same trend of achene yield caused by
various treatment combinations, maximum achene yield was caused by C2P2 (67%)
when seed inoculated with KS42 and receive foliar spray of chemicals i.e.,
GB at VS and FS) followed by C2P1 (42%), C1P2 (37%) and C0P2 (30%). Conversely,
a minimum achene yield was recorded from C0P0 (without seed inoculation of rhizobacteria
i.e., KS7 and KS42 and foliar spray of chemicals i.e., SA and GB
at VS and FS). The interactive effect between varied moisture regimes (M) and
various combinations of rhizobacteria with chemical agents (CP), M x CP, was
found significant on achene yield during consecutive years i.e. 2016 and
2017 (Table 4). During 2016, the results illustrated that maximum achene yield
was recoded from M0C2P2 (irrigated regime; seed inoculation of KS42 and foliar
spray of chemicals i.e., GB at VS and FS) followed by M0C2P1 which
produced statistically at par results with M0C1P2. Whereas, minimum achene
yield was recorded from M1COP0 (rainfed regime; un-inoculated and did not
receive application of SA and GB at VS and FS). The rest of the treatments
significantly enhanced achene yield when compared with control, but found
statistically at par results with M0C0P0, M1C1P2 and M1C1P2. In 2017, the same
trend of total soluble sugar was found with various treatment combinations of
rhizobacteria and chemical agents, maximum achene yield was recoded from M0C2P2
(irrigated regime; seed inoculation of KS42 and foliar spray of chemicals i.e.,
GB at VS and FS). Whereas, minimum achene yield was recorded from M1C0P0
(rainfed regime; un-inoculated and did not receive application of SA and GB at
VS and FS).
Discussion
In present study, it is obvious from the results that
seed inoculation of rhizobacteria combined with exogenous application of
chemicals under varied moisture regimes may assist sunflower plants in
alleviating adverse effects of drought stress. Leaf relative water contents
were significantly reduced under rainfed regime (water stressed) compared to
irrigated regime (well-watered). This decrease in LRWC correspond to the
earlier reports that water relations disturbed under water deficient condition
elucidated a considerable reduction in RWC under water stressed conditions. The
declined leaf water status implies loss of turgor that restrict cell expansion
and growth of plants (Farooq et al.
2009; Castillo et al. 2013), but it
was noticeably improved when crop was grown with seed inoculation ACC deaminase
rhizobacteria i.e., KS7 and KS42 and receive foliar spray of chemicals i.e.,
GB at bud and flower initiation stage. These results are in conformity with
earlier illustrated report that inoculation of PGPR and exogenous application
of SA and GB acid improve RWC under drought stress, the increase in LRWC under
water deficit conditions may be associated to modifications in sensitivity of
physiological processes including of stomatal closure, proliferated lateral
roots with high density and longer root hairs, which result in increased exchange
surface area with soil, and higher water flux from whole root system up to the
leaves through amelioration of tissue water status, principally due to enhanced
osmotic adjustment in response to accumulation osmolytes (Dodd et al. 2010; Kechid et al. 2013; Grover et al.
2014; Zhang et al. 2014; Gontia-Mishra
et al. 2016; Latif et al. 2016; Liu et al.
2017).
Crop water relations were adversely affected because of
decline in moisture under rainfed regime. Plants promptly respond when exposed
to drought stress by lowering of osmotic potential as an adaption strategy to
combat water deficit conditions (Subbarao et al. 2000) which is
attributed to accumulation of solutes in cells for osmotic adjustment (Bray
1997). It is obvious from the results of present study that seed inoculation of
rhizobacteria cum exogenous application of SA and GB caused a significant
amelioration in leaf osmotic potential, which was more pronounced under rainfed
regime. Improvement in turgor potential in response to seed inoculation of
rhizobacteria i.e., KS7 and 42 with exogenous application SA and GB
might be directly related to enhanced leaf water potential and high negative
leaf osmotic potential which helped plants to withstand water deficient
conditions. Lowering of leaf osmotic potential by seed inoculation of
rhizobacteria with exogenous application of SA and GB might be attributed to
accumulation organic solutes like, Proline, GB and total soluble sugars etc.,
which then ameliorated the osmoregulation ability of crop under water deficit
conditions (Farooq et al. 2009, 2010;
Sandhya et al. 2011). Osmotic
adjustment is considered as an effective component of drought resistance that
assist crop plants under water limited conditions. Osmotic adjustment involves
the net accumulation of solutes in a cell in response to a fall in the water
potential of the cell’s environment, as a consequence, the osmotic potential of
the cell is lowered, which gradient for water influx into the cell and tends to
maintain turgor pressure. Improved tissue water status may be achieved through
osmotic adjustment or changes in cell wall elasticity. This is essential for
maintaining physiological activity for extended period of drought. Changes in
tissue elasticity in response to drought, which modify the relationship between
turgor pressure and cell volume, might contribute to drought tolerance, as
observed in sunflower (Kramer and Boyer 1995; Maury et al. 2000) and common bean (Zlatev
2005).
Water use efficiency was appreciably reduced under
rainfed condition when compared with irrigated regime. Our results are in
accordance with the Reza et al.
(2014) reported that a decline in water use efficiency of sunflower under water
deficit conditions. The improvement in WUE in response to seed inoculation of
rhizobacteria and foliar spray of chemicals i.e., GB might be attributed
to increase in yield as same amount of water utilized by all treatments
including of control when seed was not inoculated and crop did not receive any
foliar spray of chemicals i.e., SA and GB. This improvement in WUE by
seed inoculation of rhizobacteria and foliar spray of chemicals i.e., SA
and GB was also previously described by (Belimov et al. 2009; Shahbaz et al.
2011; Zoppellari et al. 2014)
The present study results revealed that leaf free
proline, glycine betaine and total soluble sugars were increased when moisture
contents declined under rainfed regime. These results comply with (Manivannan et al. 2007) reported that a significant
increment in free proline, glycine betaine and total soluble sugars in
sunflower plants under water stressed conditions. The accumulation of
compatible solutes in plants when exposed to water stressed conditions is one
of the universal responses that plants exhibit and its role in acclimation of
plants is well accredited (Agboma et al. 1997; Raymond and Smirnoff
2002). Seed inoculation of rhizobacteria cum exogenous application of chemicals
i.e. SA and GB enhanced free proline, glycine betaine and total soluble
sugars under varied moisture regimes. Our results comply with earlier described
reports that rhizobacteria and chemicals i.e., SA and GB improved free
proline, glycine betaine and sugars in plants when exposed to drought stress (Heidari et
al. 2012; Naeem et al. 2011;
Sandhya et al. 2011; Dawood and Sadak
2014; Ma et al. 2014; Jalaludin et al.
2015; Zaidi et al. 2015; Gontia-Mishra
et al. 2016; Tiwari et al. 2016; Vurukonda et al.
2016). The role of osmolytes accumulated under water stressed conditions
might be related to improvement in osmoregulation that mainly assist plants to
withstand water deficit conditions through its protective role as a compatible
solute and the stabilization of macromolecules which allows root growth and
photosynthesis during drought stress (Delauney and Verma 1993; Verbruggen and
Hermans 2008; Blum 2011). Amongst, various modifications that plants adapt to
withstand drought stress, osmotic adjustment (OA) is considered as basic stress
tolerance mechanism which is accomplished through production of various organic
solutes (Serraj and Sinclair 2002).
Water deficit caused a significant reduction in achene
yield when moisture contents declined under rainfed regime as compared with
irrigated regime. Our results are in conformity with Buriro et al. (2015) reported
that water stress had severe negative effect on seed yield of sunflower.
The limited water supply caused significant decline in yield trait of crops
which might be related to impaired gas exchange properties of leaf which not
only reduce the size of source and sink tissues but had negative effect on
phloem loading, assimilate translocation and dry matter portioning (Farooq et al. 2009). However, the seed
inoculation of rhizobacteria and chemical agents i.e. SA and GB improved
achene yield under varied moisture regimes. The improvement in achene yield was
more pronounced at rainfed regime as compared with irrigated regime. The
results of achene yield obtained in our investigation are in accordance with
the earlier illustrated report by (Dey et
al. 2004; Arshad et al.
2008; Arzanesh et al. 2011; Ahmad et
al. 2014; Osman 2015; Noreen et
al. 2017). This increase in achene yield might be correlated to
accumulation of compatible solutes in response to seed inoculation of
rhizobacteria and chemical agent’s i.e.,
SA and GB which caused improvement in osmotic adjustment under water deficit
condition. Plants accumulate compatible solutes in the cell to lower down
osmotic potential which improve water influx into the cell to maintain turgor
potential. This osmotic adjustment might have helped plants in bringing about
different cell organelles and cytoplasmic activities at normal rate which
ultimately improved growth, photosynthesis and assimilate partitioning to grain
filling (Ludlow and Muchow 1990; Subbarao et al. 2000; Compant et al. 2010).
Conclusion
Moisture conditions during rainfed regime caused a
significant reduction in plant water relations, WUE and achene yield of
sunflower. Nevertheless, various combinations of seed inoculation of ACC
deaminase rhizobacteria i.e. KS7 and KS42 with exogenous application of
chemical agents i.e. salicylic acid and glycine betaine appreciably
ameliorated the negatively impaired traits under normal and water stressed
conditions. While the extent of increment caused over control was more
pronounced with treatment combinations KS42+GB, KS7+GB, KS42+SA and KS42. The
role of PGPR with chemical agents might be further explored by investigation of
key enzymes and gene expression involved in metabolism and their relationship
to drought tolerance in plants inoculated with ACC deaminase rhizobacteria KS7
and KS42 and also receive foliar spray of chemicals i.e. SA and GB could
provide key insights for induction of drought tolerance in sunflower.
Acknowledgements
The corresponding and first author is thankful to Soil
Biology and Physics Programmes, Land Resources Research Institute, NARC for
providing of rhizobacteria stains and TDR (Time Domain Reflectometry). The
author is also grateful to Central Laboratory at PMAS- Arid Agriculture
University, Rawalpindi and Plant Sciences Laboratory at Quaid-e-Azam
University, Islamabad for extended support in analysis work.
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