Journal of Biodiversity and Environmental Sciences (JBES) ISSN: 2220-6663 (Print) 2222-3045 (Online) Vol. 1, No. 2, p. 22-36, 2011 http://www.innspub.net RESEARCH PAPER
OPEN ACCESS
Morphological and physiological attributes associated to drought tolerance of Ethiopian durum wheat genotypes under water deficit condition Ashinie Bogale1*, Kindie Tesfaye2, Tilahun Geleto3 1,3
Oromia Agricultural Research Institute, PO Box 312 code 1250, Addis Ababa, Ethiopia. Haramaya University, Department of Plant Sciences, PO Box 138, Dire Dawa, Ethiopia.
2
Received: 11 January 2011 Revised: 12 February 2011 Accepted: 14 April 2011
Key words: Durum wheat, leaf gas exchange, chlorophyll fluorescence, relative water content. Abstract The experiment was conducted to assess the differential morpho-physiological response to stimulated water deficit and to determine the relationship between some of these morphological and physiological traits and yield components of eighteen durum wheat genotypes grown in pots under lathhouse condition. Water deficit significantly affected gas exchange and chlorophyll fluorescence parameters. It reduced the net photosynthesis rate (P n), transpiration rate (E) and stomatal conductance (gs) measured both at anthesis and grain-filling stages. Similarly, the value of initial fluorescence (Fo) was increased while variable fluorescence (Fv), maximum fluorescence (Fm) and optimum quantum yield fluorescence (Fv/Fm) were decreased under water deficit. RWC of the leaves was decreased by 36.7% while SLA increased by 12.6% due to moisture stress relative to the well-watered control. No significant correlations were found between chlorophyll fluorescence parameters and grain yield under water deficit condition. Similarly, no significant correlations were found between leaf gas exchange parameters and grain yield. On the other hand, peduncle length and excursion were positively correlated with grain yield while negatively correlated with drought susceptibility index under water deficit condition. Leaf posture and rolling had also a profound effect on grain yield and other attributes. Erectleaved genotypes had more grain yield, HI, kernel numbers per spikelet and grain-filling rate but had lower kernel weight than droopy leaved. Similarly, genotypes exhibited strong leaf rolling under water deficit condition had more grain yield, kernel numbers per spike and water use efficiency. The genetic variability found for leaf posture, leaf rolling, peduncle length and excursion among the Ethiopian durum wheat genotypes suggests the opportunity for selection superior and adapted genotype in water-limited environments. These can be achieved by integrating these morphological traits as indirect selection in conjunction with other yield components.
*Corresponding Author: Ashinie Bogale
[email protected]
22 | Bogale et al.
Introduction
photosynthetic apparatus to environmental stress
Drought is one of the most common environmental
(Maxwell and Johnson, 2000). Dark-adapted values
stresses that limit durum wheat production in
of Fv/Fm reflect the potential quantum efficiency of
drought-prone areas of Ethiopia. Changes in global
PSII and are used as a sensitive indicator of
climate are forecast to increase the extension of
photosynthetic performance, with optimal values of
drought-prone areas. A viable solution for crop
around 0.832 measured from most plant species
production in these areas is to develop drought
(Johnson et al., 1993). Values lower than this are
tolerant varieties. A physiological approach would be
measured when the plant is exposed to stress,
the most attractive way to develop new varieties
indicating a particular phenomenon of photo-damage
(Araus et al., 2008), but breeding for specific, sub-
to PSII reaction centers, and the development of
optimal
slowly relaxing quenching process (Maxwell and
environments
involves
a
deeper
Johnson, 2000; Baker and Rosenqvist, 2004) which
understanding of yield-determining process.
reduce Photosynthesis, which is the most significant process
the
maximum
efficiency
of
PSII
photochemistry.
influence crop production, is also inhibited by drought stress. Studies have shown that the photosynthetic
There are also several approaches to investigate
rate (Pn) of leaves of both C3 and C4 plants decreases
morphological traits for the purpose of increasing
as relative water content (RWC) and water potential
yield under water-limited conditions. Leaf rolling,
(Ψ) decrease (Cornic and Massacci, 1996). Limitation
induced by loss of turgor and poor osmotic
of net photosynthetic rate in low moisture stressed
adjustment
plant is mainly through stomatal closure (Cornic and
avoidance
Massacci, 1996; Cronic, 2000) and/or by metabolic
drought condition, leaf rolling decreased stomatal
impairment (Flexas and Medrano, 2002). The relative
closure (O’Toole et al., 1979). The erectophile leaf
magnitude of stomatal and non-stomatal factors
canopy has been also proposed as a trait that could
limiting photosynthesis depends on the severity of
increase crop yield potential by improving radiation
drought. High photosynthetic rate is considered to be
use
one of the most important breeding strategies for crop
(Reynolds et al., 1999). Peduncle length has been also
improvement (El Hafid et al., 1998; Richards, 2000).
suggested as useful indicator of yield capacity in dry
However,
leaf
environments. Kaya et al. (2002) have been found a
photosynthesis has not generally improved the yield
strong positive correlation between peduncle length
in favorable environments, most probably because the
and grain yield. In other cases, such relationship has
source is less limiting than the sink (Abbad et al.,
been found inverse (Briggs and Aytenfisu, 1980) or no
2004) and greater success might be expected for
relationship (Villegas et al., 2006) depending on the
higher rates under water stress.
environment.
Chlorophyll fluorescence analysis may also provide a
The effect of water stress on the yield and yield
sensitive indicator of stress condition in plants. It can
components of durum wheat at different growth
also be used to estimate the activity of the thermal
stages have been the subject of many studies (Simane
energy dissipation in photosystem II, which protects
et al., 1993; Solomon et al., 2003). However, no study
photosytems from the adverse effect of light and heat
had been conducted on the physiological and
stress. The measurement of chlorophyll fluorescence
morphological response of diverse Ethiopian durum
in situ is a useful tool to evaluate the tolerance of the
wheat
selection
for
higher
rates
of
represents mechanism
efficiency
23 | Bogale et al.
in
genotypes
an
(Richards,
high
to
important
radiation
water
drought-
1996).
Under
environments
deficit
conditions.
Therefore, the present study aims to determine water
each pot every other day for a period of a month until
deficit effects on leaf gas exchange and chlorophyll
the plants reach four leaf growth stages.
fluorescence parameters in leaves of eighteen durum wheat (Triticum tugidium L. durum) genotypes and
Water deficit treatment
to
some
Following the Zadock’s scale [Zadock et al., 1974],
morphological and physiological traits and yield
plants were subjected to water stress at different
under water deficit conditions.
growth stages: stress continuously from tillering to
determine
the
relationship
between
physiological maturity (M1), stress from anthesis to
Materials and methods
physiological maturity (M2), and stress from grain-
Plating materials
filling stage to physiological maturity (M3) and well-
The study was conducted in a lathhouse at Sinana
watered control (C) treatments. The water levels were
Agricultural Research Center (SARC) during the
maintained in the range of 35-50% field capacity in
7’N latitude,
the stress treatments while above 75% in the control
10’ E longitude and 2400 m.a.s.l altitude in Bale
treatment. These water stress conditions are designed
Zone of Oromia Region, Ethiopia. To embrace the
to simulate the environments that experience very low
variability existing among the Ethiopian durum wheat
water supply after crop establishment in different
genotypes, three landrace [B5-5B, S-17B, and WA-13],
parts of the country. During the stress period, plants
thirteen commercial cultivars [Asassa, Bekelcha,
were left without water for 12 days by withholding
Boohai, Egersa, Foka, Gerardo, Ilani, Kilinto, Obsa,
irrigation until early morning wilting is observed.
Oda, Quamy, Tob-66 and Yeror] and two advanced
Then pots were weighted and irrigated until the
lines from the breeding program [CDSS93Y107 and
weight of every pot became equal to the weight of the
CD94523] were used for this study. The examined
predetermined water level. The amount of water
genotypes are different in genetic background, origin
depleted from pots was obtained by weighing pots
and several characteristics.
every two to three days, and the loss in weight was
2006/07 main season. It is located at 400
70
restored by watering pots with the amount of water equal to the loss in weight.
Experimental design Plants were grown in 21 cm diameter and 18 cm length plastic pots filled with a textural class of clay
Gas exchange parameters
(49.7% clay, 27.3% silt and 23% sand). Each pot was
Gas exchange was measured on the flag leaves of
filled with 4 kg uniformly air-dried soil (17.1%
fully-grown stressed and unstressed of the main tiller
moisture). The field capacity and permanent wilting
of
point of the soil were 47.8% and 11.5%, respectively.
photosynthesis system (CI-301PS CO2 Gas Analyzers,
Pots were arranged in Randomized Complete Block
CID Inc., 1996, USA). The traits measured were net
Design (RCBD) in factorial combination of the
photosynthetic rate (Pn), stomatal conductance (gs),
eighteen genotypes and four water regimes with three
transpiration rate (E), and internal carbon dioxide
replications. A total of 216 pots, 12 pots were assigned
concentration (Ci). In addition, apparent mesophyll
to each genotype. 2g N and 2 g P2O5 fertilizers were
conductance (the conductance of CO2 from the
applied to each pot during planting and additional 0.5
stomatal cavity to the chloroplast) was determined as
g N was applied at the first tillering. Planting was
the ratio Pn and Ci following the procedure of Fischer
done on August 10, 2006. Eight seeds were sown per
et al. (1998) to produce information on the relative
pot and the seedlings were thinned to four at two leaf
importance of the mesophyll limitation to Pn.
growth stages. Five hundred ml of water was added to
Instantaneous water use efficiency (iWUE) was also
three
24 | Bogale et al.
plants
per
pot
using
a
portable
calculated as the ratio of net photosynthesis rate to
s-1 provided by an array of six light emitting diodes
transpiration rate. Measurements were made on non-
(peak 650 nm). Measurement was performed during
overcast days at 9:00 - 11:00 am at anthesis and grain
day time (between 10:00 and 4:00).
filling stages. Morphological parameters Relative water content (RWC)
Rolling of leaves under stressed condition was also
RWC was measured from flag leaves at anthesis.
assessed visually using 1 to 3 scale (1 = no rolling of
Immediately after cutting at the base of lamina, leaves
leaf, 2 = intermediate rolling and 3 = complete
were sealed within plastic bags and transferred to the
rolling) and leaf posture was assessed visually using 1
laboratory. Fresh weight (FW) was measured after
to 3 scale (1 = erect, 2 = semi-erect and 3 = droopy).
excision and the full turgid weight (TW) after the
Peduncle length (cm) was determined as average
dehydration of the leaves by placing them in a test
height of peduncle from the last node of the main
tube containing 100 ml distilled water for 24 h at
stem to the initial tip of the spike and peduncle
room temperature (about 21°C). After soaking, leaves
excursion was measured as the distance from the flag
were carefully blotted dried with tissue paper. Dry
leaf ligule to the base of spike from four plants per
weight (DW) was measured after oven drying at 70 0C
pot.
for 72 hrs. The RWC was calculated from the equation given by Schonfeld et al. (1988) as: RWC = (FW-DW)/
Yield and yield component
(TW- DW) x 100, where FW, TW and DW are fresh,
Data were also collected for number of kernels per
turgid, and dry weight of the leaf, respectively.
spike, 100 kernel weight, spike length, air-dried aboveground biomass and grain yield per plant.
Specific leaf area (SLA) and kernel ash content
Harvest index was determined as the proportion of
(GaMa)
grain yield to the overall aboveground biomass per
SLA of the flag leaf was also determined as the ratio of leaf area
(cm2)
plant.
to dry mass (g). Kernel ash content
which is expressed in dry weight basis (%), was
Crop water use efficiency
determined
complete
WUE was determined as the ratio of grain yield to
combustion of the grain powder at 575 0C for 16 h
seasonal plant water use. The seasonal water use was
(until light gray ash was obtained) in a muffle electric
obtained by summing up the difference in soil water
furnace and then the weight the residue was recorded.
between measurements just before and after irrigation
from
the
kernel
after
of each pot. Chlorophyll fluorescence The polyphasic rise of fluorescence transients was
Statistical data analysis
measured at tillering, anthesis and grain filing stage
The data were subject variance analysis using SAS
using a portable Plant Efficiency Analyzer (PEA,
GLM procedure release 8.02 (SAS Institute Inc.,
Hansanthech, UK) from three leaves per pot. The
2001). Means comparisons were carried out to
initial fluorescence (Fo) and maximal fluorescence
estimate the differences between water
(Fm), variable fluorescence (Fv) and
maximal
treatments and genotypes using Duncan’s Multiple
photochemical efficiency of PSII (Fv/Fm) were
Range Test. Linear correlation analyses were used to
measured immediately after dark-adapted the leaves
determine the association between grain yields,
for 30 minute using leaf clips provided with PEA. The
physiological and morphological traits using SPSS.
transients were induced by red light of 3000 μmol
m-2
25 | Bogale et al.
deficit
Results Leaf gas exchange parameters
Table 1.
Mean value of photosynthetically active
radiation
(PAR),
net photosynthetic rate
(Pn),
transpiration rate (E), stomatal conductance (gs) and
The photosynthetically active radiation (PAR) level
instantaneous water use efficiency (iWUE) of durum
during measurement both at anthesis and grain-filling
wheat genotypes grown under water deficit and well-
stages was greater than the saturating photosynthetic
watered conditions during anthesis and grain-filling
capacity of wheat crop (i.e. 1500 µmol m-2 s-1) (Blum,
stages.
1990). Water deficit treatment both at anthesis and grain-filling stages significantly affected the gas
Growth PAR Pn E gs iWUE stage (µmol m- (µ mol m-2 (mmol m-2 s- (mmol m-2s-1) (µ mol 2 s-1) -1 1 s ) ) /mmol)
exchange parameters. The reduction was more pronounced at grain-filling stage. Pn and E were reduced by 30.2% and 52.3% due to the stress induced at anthesis as compared to the control treatment, respectively. It reduced by 59.0% and 71.7% as compared to the control treatment at grain-filling stage, respectively (Table 1). Similarly, the stomatal conductance
was
reduced
by
44.2%
while
instantaneous water use efficiency was significantly increased as compared to the control at both stages. An increase in iWUE could be due to more reduction in E than Pn by water deficit. The ratio of intercellular to ambient CO2 concentration (Ci:Ca) and the internal CO2 concentration were not affected by water deficit induced at anthesis and grain-filling stages (Table 2). Variability for net photosynthesis rate, stomatal and mesophyll conductances and instantaneous water use efficiency was observed among genotypes both at anthesis and grain-filling stage (Table 2).
Anthesis Grainfilling Mean
(µ S molCm2 s-1)(µ 1994.8 mol 8.1 m 11.6 -2 s1) 2084.8 4.3 10.5
0.42
0.88 109.1 195.5 28.8 15.8
0.15
0.53 43.9 115.8 33.5 23.5
2039.8 6.2 11.1
0.29 0.71 76.5 155.7 31.2 19.7
S
C
S
C
S
C
S-Stress, C-Control
Relative water content, specific leaf area and ash content The mean values of the RWC across genotypes under well watered and water deficit treatments were 87.6% and 55.7%, respectively. Water deficit caused a 36.7% reduction of the RWC of the leaves but genotypes were varied in maintaining their RWC under both water deficit and well-watered conditions. Specific leaf area (SLA) was significantly influenced by water regimes and genotypes but not by their interaction (Table 2). The SLA of all the genotypes was increased under water deficit by an average value of 12.6% relative to the well-watered treatment. Mean ash
No significant correlations were found between net photosynthesis rate and stomatal conductance and photosynthesis and transpiration rates (at both stages under stress and well-watered conditions. Similarly, no overall correlations were found between Pn and gs and Pn and Ci:Ca both under stress and well-watered conditions. However, strong correlations were noted between net photosynthesis rate and mesophyll conductance under both stress (r = 0.603, P
