Phenotyping Root System Architecture of Cotton (Gossypium barbadense L.) Grown Under Salinity

Abstract

Soil salinity causes an annual deep negative impact to the global agricultural economy. In this study, the effects of salinity on early seedling physiology of two Egyptian cotton (Gossypium barbadense L.) cultivars differing in their salinity tolerance were examined. Also the potential use of a low cost mini-rhizotron system to measure variation in root system architecture (RSA) traits existing in both cultivars was assessed. Salt tolerant cotton cultivar ‘Giza 90’ produced significantly higher root and shoot biomass, accumulated lower Na+/K+ ratio through a higher Na+ exclusion from both roots and leaves as well as synthesized higher proline contents compared to salt sensitive ‘Giza 45’ cultivar. Measuring RSA in mini-rhizotrons containing solid MS nutrient medium as substrate proved to be more precise and efficient than peat moss/sand mixture. We report superior values of main root growth rate, total root system size, main root length, higher number of lateral roots and average lateral root length in ‘Giza 90’ under salinity. Higher lateral root density and length together with higher root tissue tolerance of Na+ ions in ‘Giza 90’ give it an advantage to be used as donor genotype for desirable root traits to other elite cultivars.

Full text

PHENOTYPING ROOT SYSTEM ARCHITECTURE OF COTTON (GOSSYPIUM
BARBADENSE L.) GROWN UNDER SALINITY
SHADY A. MOTTALEB1*, ESSAM DARWISH1, MENNA MOSTAFA2, AND GEHAN SAFWAT2
1Cairo University, Egypt
2October University for Modern Sciences and Arts, Egypt
MOTTALEB, S.A. – DARWISH, E. – MOSTAFA, M. – SAFWAT, G.: Phenotypic root system architecture of cot-
ton (Gossypium barbadense L.) grown under salinity. Agriculture (Poľnohospodárstvo), vol. 63, 2017, no. 4, pp.
142–150.
Shady A. Mottaleb (*Corresponding author), Essam Darwish, Agricultural Botany Department – Plant Physiology Division,
Faculty of Agriculture, Cairo University, Egypt. E-mail: shady.osama@agr.cu.edu.eg
Menna Mostafa, Gehan Safwat, Faculty of Biotechnology, October University for Modern Sciences and Arts, Egypt
Key words: Gossypium barbadense L., salinity stress, phenotyping, root system architecture
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Agriculture (Poľnohospodárstvo), 63, 2017 (4): 142−150
DOI: 10.1515/agri-2017-0014Original paper
Soil salinity causes an annual deep negative impact to the global agricultural economy. In this study, the effects of salinity
on early seedling physiology of two Egyptian cotton (Gossypium barbadense L.) cultivars differing in their salinity tolerance
were examined. Also the potential use of a low cost mini-rhizotron system to measure variation in root system architecture
(RSA) traits existing in both cultivars was assessed. Salt tolerant cotton cultivar ‘Giza 90’ produced signicantly higher root
and shoot biomass, accumulated lower Na+/K+ ratio through a higher Na+ exclusion from both roots and leaves as well as
synthesized higher proline contents compared to salt sensitive ‘Giza 45’ cultivar. Measuring RSA in mini-rhizotrons contain-
ing solid MS nutrient medium as substrate proved to be more precise and efcient than peat moss/sand mixture. We report
superior values of main root growth rate, total root system size, main root length, higher number of lateral roots and average
lateral root length in ‘Giza 90’ under salinity. Higher lateral root density and length together with higher root tissue tolerance
of Na+ ions in ‘Giza 90’ give it an advantage to be used as donor genotype for desirable root traits to other elite cultivars.
Soil salinity is estimated to cause losses in crop
production of about 27.3 billion US dollars annu-
ally (Qadir et al. 2014). The effects that excess
Na+ cations present in saline soils have on plant
physiology are devastating, ranging from ion tox-
icity and physiological drought to reactive oxygen
species (ROS) formation and cell death (Munns &
Tester 2008). Although plants have developed a set
of strategies to tolerate salinity stress (Roy et al.
2014), the majority of economically important crop
plants are considered glycophytes and are severely
affected by high Na+ concentration with an evident
trade-off between yield and salinity tolerance.
Salinity tolerance among cotton germplasm var-
ies widely, both intra- and interspecically where,
for example, Gossypium barbadense varieties were
reported to be more tolerant to salinity than Gos-
sypium hirsutum or Gossypium arboreum cottons
(Abul-Naas & Omran 1974). Phenotypic variability
of cotton root traits was reported to be present for
root weight, length, volume, total dry matter, and
shoot-to-root ratio in G. hirsutum germplasm (Basal
et al. 2003; Aboukheir et al. 2008). However, not
only very little is known about phenotypic variabil-
ity of other important RSA traits such as lateral root
length and density but also assessing its available
variability in Egyptian cotton (G. barbadense), an
economically valuable species, is lacking.
Plant root system architecture (RSA), the spatial
distribution of the root system within the rooting
volume, controls the fate of the plant through its ef-
ciency of anchorage to the soil as well as water,
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Agriculture (Poľnohospodárstvo), 63, 2017 (4): 142−150
nutrients uptake and abiotic stress tolerance. Mod-
ifying RSA traits was reported to contribute in im-
proving grain yield and drought tolerance (Steele et
al. 2013; Uga et al. 2013). Nevertheless, studying
RSA is difcult regarding root sampling measure-
ment, and plasticity in response to various envi-
ronmental stimuli (Julkowska & Testerink 2015).
Several methods have been proposed to study RSA,
including hydroponics (Tuberosa et al. 2002), rhi-
zotrons (Devienne-Barret et al. 2006), mini-lysime-
ters (Udayakumar et al. 1998), and PVC tubes (Tay-
lor et al. 1991).
The present study aims to investigate the exis-
tence of variability in RSA under salinity stress in
Egyptian cotton as well as identify potential new
traits benecial for salinity tolerance. Using a mor-
phological and physiological approach to study two
Egyptian cotton cultivars differing in salinity tol-
erance, cv. ‘Giza 45’ (salt sensitive) and cv. ‘Giza
90’ (salt tolerant), evidence will be provided that
phenotypic variability in RSA is present in Egyp-
tian cotton cultivars. Also, the possibility of phe-
notyping this variability will be described using a
simple mini-rhizotron system. Finally some recom-
mendations on the optimum type of substrates and
conditions to be used for an accurate phenotyping
of Egyptian cotton roots at seedling stage are given.
MATERIAL AND METHODS
The present study was carried out during Janu-
ary–July 2016 in the Plant Physiology division, De-
partment of Agricultural Botany, Faculty of Agricul-
ture, Cairo University, Egypt.
Plant material
Egyptian cotton (Gossypium barbadense L.)
cultivars ‘Giza 90’ (salt tolerant) and ‘Giza 45’(salt
sensitive) were used in our experiments, both ob-
tained from the Cotton Research Institute, Agricul-
tural Research Centre, Giza, Egypt.
Mini-rhizotron description
Mini-rhizotron system allows a non-destructive
study of root development during early stages of
seedling growth. It usually contains a thin layer of
substrate that directs the roots to grow in 2D condi-
tions, facilitating the monitoring and measurement
of root system morphology and architecture. The
mini-rhizotron used in our experiments consisted of
two glass sheets of 30 × 30 cm separated by a 3 mm
wide glass separator. The inner space available for
culture substrate was approximately 250 cm3.
Experimental design and plant growth conditions
Experiments were arranged as a randomized
design with 3–5 replicates, and were repeated two
times to conrm results. Two different experiments
were performed using this mini-rhizotron in the
present research work as follows:
Experiment 1
The substrate of this experiment included peat
moss and sieved ne sand mixture (2:1). After the
mini-rhizotron was lled with the substrate, the two
glass sheets were placed over each other and sealed
from the corners and below with paper clips and
sellotape to keep substrate from being lost and was
perforated at the bottom to allow drainage. Mini-rhi-
zotrons were kept in a growth chamber under the
following conditions: 25°C, 60% humidity, photon
irradiance of 100 µE/m2/s and 16/8h light/dark cy-
cle). Mini-rhizotrons were placed vertically under
the angle of 70° in the growth chamber and covered
with black plastic bags to provide dark conditions
for roots.
Experiment 2
The substrate placed in mini-rhizotrons of this
experiment consisted of sucrose-free ¼ strength MS
medium (Murashige & Skoog 1962) supplemented
with agarose gel 1.2% and pH was adjusted to 5.8.
The same growing conditions were maintained as
experiment 1.
Seed sterilization and cultivation
Seeds were sterilized in commercial sodium hy-
pochlorite solution 1% for 10 min and then rinsed
three times with tap water, and then left to germinate
for two days in Petri dishes lined with water-soaked
lter paper. In both experiments, one germinated
seed from cultivar Giza 90 was planted at approx-
imately equal spacing from the other cultivar Giza
45 per mini-rhizotron.
Salinity stress treatment
In Experiment 1, two days old seedlings were
transferred to mini-rhizotrons and randomly divided
into two groups. The rst group was the control and
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was watered with 100 ml of ¼ MS medium every
two days during the two weeks. The second group
was treated with ¼ MS medium containing 150 mM
NaCl every two days also for two weeks.
In Experiment 2, using mini-rhizotron containing
solid MS nutrient medium, salinity stress was im-
posed from the beginning using solid ¼ strength MS
medium containing 150 mM NaCl, where 2 days old
seedlings of both cotton cultivars were transferred
to four mini-rhizotrons. In the case of control condi-
tions, another four seedlings of both cultivars were
transferred to NaCl free solid ¼ strength MS medi-
um.
Salinity tolerance physiological traits
Leaf relative water content (RWC) was calcu-
lated according to Weatherly (1950). Fresh and dry
weights were determined with the accuracy of 0.001 g
on the regular lab scale. Dry weight of root and
shoot tissues were measured after drying the ma-
terial for 48 h at 70°C. Free proline concentration
in leaves was determined according to Bates et al.
(1973) using 0.5 g dry weight samples. Na+ and K+
cation contents of shoot or root dry weight samples
were extracted by 0.1 M HCl solution (Garciadeb-
las et al. 2003). Determination of Na+ and K+ cat-
ion contents was realized using a ame photometer
(Jenway PFP-7, Bibby Scientic Limited, UK).
Image capturing and analysis of RSA
Mini-rhizotrons were scanned with a Canon
MG2400 series Scanner at 200 dpi at 14 days plant
age. Scanned images RSA parameters were pro-
cessed and quantied using EZ-Rhizo software (Ar-
mengaud et al. 2009). Data were collected from 3
individual seedlings per treatment per experiment.
RSA parameters of control conditions were not
quantied, since the roots were too entangled for the
EZ-Rhizo software to detect. All data were cleared
from outliers.
Statistical analysis of data
Differences among means were tested by a two-
way ANOVA followed by Duncan post hoc test. In
the case of RSA parameters, differences between
means were tested by t-test. Differences were con-
sidered statistically signicant at P < 0.05 in all
analyses. Both statistical analyses were carried out
using IBM SPSS Statistics V. 20 (IBM, USA).
RESULTS
Cv. ‘Giza 90’ accumulates lower Na+ and higher
proline contents than ‘Giza 45’
RWC was signicantly decreased by almost 10%
under 150 mM NaCl treatment in both cultivars but
with no differences between them (Table 1). Never-
theless, salinity treatment signicantly increased the
content of Na+ but not K+ in both shoots and roots as
compared to plants under control conditions. These
increases in Na+ concentrations were signicantly
higher in cv. ‘Giza 45’ making it less efcient than
cv. ‘Giza 90’ in eliminating Na+ to the outside of
root cells. This was reected by a signicantly less
decrease in K+ / Na+ ratio in cv. ‘Giza 90’ roots un-
der salinity. However, cv. ‘Giza 90’ showed similar
values to “Giza 45” under control conditions. In ad-
dition, the ability to synthesize proline under salini-
ty stress in cv. ‘Giza 45’ was found to be signicant-
ly lower than cv. ‘Giza 90’. Leaf proline contents of
cv. ‘Giza 90’ were one-fold higher than cv. ‘Giza 45’
under salinity stress, being ca. 1.93 and 4.17 mg/g
leaf dry weight basis in cvs. ‘Giza 45’ and ‘Giza 90’,
respectively. Surprisingly, the synthesis of proline in
cv. ‘Giza 90’ leaves under control conditions was
similar to the value of cv. ‘Giza 45’ leaf proline un-
der salinity conditions.
Salinity stress severely hinders root growth rate of
cv. ‘Giza 45’
Hidden lateral roots in the thin layer of substrate
(Figure 1) made possible to only examine and mea-
sure growth of the main root of both cotton cultivars.
Root growth rate of both cultivars was signicantly
hindered under 150 mM NaCl treatment compared
with control (Table 1). Nevertheless, root system of
cv. ‘Giza 45’ was apparently more sensitive to salin-
ity as the decrease in its main root growth rate was
more signicant than cv. ‘Giza 90’ under 150 mM
NaCl, giving values of approximately 11.1 and 16.6
mm/day, respectively.
Cv. ‘Giza 90’ gives higher root and shoots biomass
under salinity
Harvesting intact root system from peat moss/
sand substrate was difcult to achieve in both treat-
ments of experiment 1, because signicant root bio-
mass was lost in harvesting. However, in mini-rhi-
zotron containing solid MS medium, the whole in-
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tact root system was easily harvested and washed.
The effect of 150 mM NaCl was detrimental to
shoots of both cultivars (Table 1) being more sig-
nicantly pronounced in the case of cv. ‘Giza 45’.
Root system architecture (RSA) traits under salinity
of cv. ‘Giza 90’ is highly superior than ‘Giza 45’
Solid MS media in mini-rhizotrons permitted a
clear and accurate measurement of the whole root
system of both cotton cultivars (Figure 2). Nonethe-
less, the vigorous growth under control treatment
led to overlapping of lateral roots of both cultivars
which prevented its analysis using EZ-Rhizo root
image analysis software (Figure 2 and Supplemen-
tary Figure 1). This, however, was not the case un-
der 150 mM NaCl, where root growth was slower
and less dense. Results in Table 2 show the effect of
salinity on RSA of both cultivars. Overall, the mor-
phology of cv. ‘Giza 90’ was considerably superior
under both control and 150 mM NaCl conditions
(Figure 2). The total root system size of cv. ‘Giza
90’ was 2.5 folds over cv. ‘Giza 45’ under 150 mM
NaCl. This was attributed to the signicantly longer
main root length of cv. ‘Giza 90’ as compared to cv.
‘Giza 45’ as well as almost a 2.5 folds bigger cu-
mulative lateral roots length. This might imply that
the effect of 150 mM NaCl on lateral roots of cv.
‘Giza 45’ was more profound and more detrimental.
This was also reected in cv. ‘Giza 45’ as a longer
main root as a ratio of total root size of ca. 45%,
which clearly demonstrates an extreme effect on lat-
eral root growth than on main root comparing with
‘Giza 90’ (ca. 19%). Finally, this was also evident in
‘Giza 90’ giving higher number of lateral roots and
average lateral root length values, which was almost
the double in size than that of cv. ‘Giza 45’ in both
cases.
DISCUSSION
Assessing salinity tolerance of ‘Giza 90’ and ‘Giza
45’ cotton cultivars
Egyptian cotton varieties are classied accord-
ing to their salinity tolerance into three groups; salt
sensitive, moderate salt tolerant and salt tolerant
(Ashour & Abd-El’Hamid 1970). Curiously, early
reports considered cv. ‘Giza 45’ salt tolerant, (El-Za-
hab 1971) while more recent reports classify it as
salt sensitive (El-Kadi et al. 2006). Thus, it was im-
portant in our work to assess the degree of seedling
stage salinity tolerance of ‘Giza 45’ and ‘Giza 90’
T a b l e 1
Salinity tolerance traits studied in cvs. ‘Giza 90’ and ‘Giza 45’ cotton plants (14 days age) under control and 150 mM NaCl
treatment (Experiments 1 and 2)
Experiment Trait Control 150 mM NaCl
‘Giza 90’ ‘Giza 45’ ‘Giza 90’ ‘Giza 45’
1
Leaf RWC [%] 82.1 ± 1.8a83.2 ± 1.5a73.5 ± 1.3b77.5 ± 0.5b
Root growth rate [mm/d] 28.0 ± 2.0a19.0 ± 1.9b16.6 ± 2.5b11.1 ± 1.0c
Leaf proline [mg/g] 2.22 ± 0.12b 1.53 ± 0.20c 4.17 ± 0.32a 1.93 ± 0.03bc
Leaf Na+ [nmol/mg] 89.8 ± 9.4 60.6 ± 7.1a430.8 ± 37.2b648.4 ± 44.4c
Root Na+ [nmo/mg] 310.5 ± 21.6a438.1 ± 61.5a716.6 ± 35.9b891.3 ± 57.3c
Leaf K+ [nmol/mg] 282.2 ± 44.5a247.5 ± 53.8a302.2 ± 28.5a301.4 ± 29.2a
Root K+ [nmol/mg] 251.1 ± 40.0a 300.5 ±16.2a394.4 ± 61.0a 343.4 ± 5.8a
Leaf K+/Na+ 3.3 ± 0.9a 4.2 ± 1.0a 0.7 ± 0.0b 0.5 ± 0.0b
Root K+/Na+ 0.8 ± 0.1a 0.7 ± 0.1ab 0.5 ± 0.1bc 0.4 ± 0.0c
2
Shoot DWT [mg] 186.5 ± 2.6a92.7 ± 4.2b 68.2 ± 10.3b25.3 ± 6.9c
Root DWT [mg] 126.2 ± 1.0a20.7 ± 1.4b104.7 ± 11.4a14.1 ± 2.7b
Shoot/Root 1.5 ± 0.7b 4.5 ± 0.5a 1.3 ± 0.6b 2.4 ± 0.6b
Each value represents the mean ± standard error of 3 replicates. Means with identical letters in the same row are not signicantly
different (P > 0.05) according to Duncan test. (Abbreviations: RWC – relative water content; DWT – dry weight)
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Figure 1. Root system morphology of cvs. ‘Giza 90’ and ‘Giza
45’ cotton plants (14 days age) under A) control and B) 150 mM
NaCl conditions (Experiment 1)
cultivars using simple physiological measurements
before starting root phenotyping.
High salinity reduces vegetative and reproduc-
tive growth of cotton (Gorham et al. 2010). Both
plant height and leaf expansion are negatively af-
fected in saline soils where the differentiation of
nodes is suppressed (Ahmed 1994). These effects
are however less accentuated in tolerant as in the
case ‘Giza 90’ where both its shoot and root biomass
are signicantly higher than cv. ‘Giza 45’. Salinity
level of 150 mM NaCl was reported to reduce the
elongation of the taproot of cotton plants by 60%
over control plants (Zhong & Lauchli 1993). The se-
verity of this level of salinity on the water relations
of both cultivars was assessed by measuring the
relative water content (RWC) in leaves (Table 1),
a trait that measures of water decit in the leaf that
reecting the dynamic water balance between water
ow into and out of the tissue (Sinclair & Ludlow
1985). It is clear that under this moderate stress, the
stomata are compelled to adjust their conductance
to maintain more or less stable water balance in the
leaves and prevent further water losses to maintain
cell and tissue turgor, and this effect was similar on
both cultivars.
The apparent higher efciency of cv. ‘Giza 90’
in Na+ exclusion or sequestration inside the cell vac-
uole might depend on the level of transcription of
transporters and activity of responsible transporters
such as SOS1 and NHX, respectively. Also, signi-
cantly lower foliar Na+ content accumulated in cv.
‘Giza 90’ was detected. This is an important trait to
protect the leaves photosynthetic machinery from
any damage induced by excessive Na+ involving
several mechanisms such as Na+ xylem loading, Na+
retrieval from the xylem and Na+ retrieval from the
shoots (Karley et al. 2000; Davenport et al. 2007).
A lower Na+ concentration in the leaves is usually
expressed in more salinity tolerance. Furthermore,
cell depolarization occurs under salinity makes K+
uptake more problematic, causing a massive K+ ef-
ux resulting in a depletion of the cytosolic K+ pool
(Shabala & Munns 2012). Nevertheless, our results
do not show any signicant perturbation in K+ lev-
els under 150 mM NaCl treatment neither in roots
nor in shoots, indicating that stress level imposed
was not very severe nor extended in time (Table 1).
Cytosolic K+/Na+ ratio, and not the absolute quanti-
ty of Na+ per se, seems to determine cell metabolic
competence and, ultimately, the ability of a plant
to survive in saline environments (Shabala & Cuin
2008) and, thus, higher K+/Na+ ratio could reect
more salinity tolerance, which might seem to be the
case in cv. ‘Giza 90’. Nevertheless, its higher K+/
Na+ ratio is attributed to a higher Na+ efux and not
from higher K+ retention (Table 1).
Under salinity, cells adjust their osmotic poten-
tial by accumulating many compatible solutes which
also perform many other important functions. Oos-
terhuis and Wullschleger (1988) reported that cot-
ton has more osmotic adjustment capabilities than
other major crops. Moreover, signicant differences
among cotton cultivars for osmotic potential exist,
suggesting that genotypic variation for osmoregu-
lation in cotton is wide (Quisenberry et al. 1982).
All in all, it is extensively reported that proline con-
centration increases in cotton with increasing soil
salinity (He et al. 2007). It is apparent that under
our experimental conditions, proline content of cv.
‘Giza 90’ is signicantly higher than cv. ‘Giza 45’,
giving it a superior ability to maintain its turgor un-
der salinity, results similarly reported by El-Kadi et
al. (2006).
Challenges in studying RSA of cotton
Root phenotype of plant seedling can be a sound
predictor of later stages of plant development (Tu-
berosa et al. 2002). However, a problem we faced
in studying roots of early stage cotton plants in
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mini-rhizotron, in contrast to other crops such as to-
mato (Darwish et al. 2016), was that some lateral
roots were either hidden into the soil layer and not
showing over neither the front nor back glass plates
of the mini-rhizotron to be scanned for subsequent
image analysis. Also, some lateral roots showed at
back side only. The main cause of this problem is
that the lateral roots of cotton emerge on the main
root in a 3D manner, which decreases the efcien-
cy of studying RSA in 2D mini-rhizotrons, as in
the case of our experiment. A possible solution to
avoid this problem is to force the growth of later-
al roots in an even more 2D growth by decreasing
the spacing between the two mini-rhizotron glass
plates even lower than 3 mm. This, however, will
probably put a mechanical strain which might affect
the main root growth making its growth pattern not
be reliable to study. Thus, solid MS medium was
used to provide a translucent environment need-
ed to detect all lateral roots and study their RSA.
Another problem we faced was that, under control
conditions, the root growth was very vigorous and
led to the overlapping and entanglement of lateral
roots in many zones (Figure 2). This problem leads
to a faulty detection of roots in Ez-Rhizo software
and gave erroneous results (Supplementary Figure
1). This could be overcome by studying RSA under
control conditions at earlier stages of growth (e.g.
10 days age). For this reason, it was only possible
for us to study the RSA of cvs. ‘Giza 45’ and ‘Giza
90’ only under salinity stress.
Identifying potential root traits in Egyptian cotton
desirable for salinity tolerance
A signicant phenotypic variability in G. hir-
sutum cotton, i.e. root length, root fresh weight,
root dry weight, lateral root number, lateral root
dry weight, total root dry weight, root volume, and
root-to-shoot ratio was reported in previous studies
(Basal et al. 2003; AbouKheir et al. 2008). This
variability, however, seems to be much lower in
genotypes adapted to humid and high-rainfall con-
ditions (Quisenberry et al. 1981). In the case of our
experiments, substantial variation in root traits was
detected between cvs. ‘Giza 90’ and ‘Giza 45’. The
analyzed data of mini-rhizotron root system imag-
es (Experiment 2) with EZ-Rhizo software (Table
2) shows that cv. ‘Giza 90’ root system architecture
Figure 2. Root system morphology of cvs. ‘Giza 45’ and ‘Giza
90’ cotton plants (14 days age) under A) 150 mM NaCl and B)
control conditions (Experiment 2)
Suppl. Figure 1. Processed image by EZ-Rhizo software
of root system morphology of cvs. ‘Giza 90’ and ‘Giza 45’
cotton plants (14 days age ) under A) control and B) 150 mM
NaCl conditions (Experiment 2). Red arrows indicate entangled
regions erroneously detected by the software
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under salinity conditions was signicantly higher in
various parameters including total root size, main
root length, cumulative lateral root length, average
lateral root length, number of lateral roots, length of
basal and branched zones, and depth. This was also
the case with main root growth rate. On the other
hand, several other parameters did not show any sig-
nicant difference such as length of apical zone and
number of lateral roots per cm of main root. These
impressive root system characteristics of the salinity
tolerant cultivar cv. ‘Giza 90’ suggest that the allo-
cation of photosynthate from the source to the roots
is more effective than in cv. ‘Giza 45’, which is -
nally translated as a higher root biomass as shown
earlier (Table 1). The body of literature published on
the effect of salinity on root traits of cotton in gen-
eral, and RSA in particular, is very limited (Gorham
et al. 2010). However, a number of different root
morpho-physiological traits have been proposed to
be implicated as important mechanisms that impart
drought tolerance in cotton, which might be bene-
cial in salinity tolerance as well. These include dis-
tance from transition zone to the rst main lateral
root, taproot weight, number of lateral roots, seed-
ling vigour, rapidity of root system development,
and root to shoot ratio and longer taproot length
(Pace et al. 1999). Our results show that cv. ‘Giza
90’ possesses several of the aforementioned traits
that are benecial under drought and probably under
salinity stress as well. For example, the production
of signicantly denser and longer lateral roots in the
top soil is desired traits and especially in saline soils
because salinity is lower at these areas and becomes
more concentrated in deeper layers. This high densi-
ty of lateral roots permits a more efcient extraction
of less salinised water from topsoil and consequent-
ly the plants become less susceptible to dehydration.
This trait present in salt tolerant cv. ‘Giza 90’ cotton
suggests its advantage as a donor genotype for this
particular desirable root trait to other elite cotton
cultivars in any of the ongoing breeding programs
for salinity and /or drought tolerance.
CONCLUSIONS
Salt tolerant ‘Giza 90’ cotton cultivar showed
superior shoot/root biomass, higher K+/Na+ ratio
and proline content. This superiority also holds true
regarding the majority of root system architecture
(RSA) parameters. The possibility of phenotyping
of cotton RSA at early stage could be predictor for
later developmental stages, using a mini-rhizotron
system which was demonstrated being more accu-
rate using solid MS media than peat moss/sand as
substrate. Phenotypic variation in potential bene-
cial root traits for salinity tolerance, such as a lon-
ger and denser lateral roots in branched zone, in the
Root system architecture (RSA) parameter ‘Giza 45’ ‘Giza 90’
Main root “MR” length [cm] 14.47 ± 0.12 19.01 ± 0.72*
Lateral roots “LR” cumulative length [cm] 19.64 ± 4.66 97.56 ± 3.98*
Total root size “cumulative length of LR and MR” [cm] 35.38 ± 6.05 120.43 ± 8.56*
Number of lateral roots per main root (#) 19 ± 0 43 ± 4*
Average length of lateral roots [cm] 0.93 ± 0.18 1.94 ± 0.17*
Average lateral root length as ratio of main root length [%] 6 ± 0 9 ± 0*
Main root length as ratio of total root size [%] 45 ± 4 19 ± 2*
Length of basal zone [cm] 1.04 ± 0.92 0.74 ± 0.54
Length of branched zone [cm] 8.42 ± 0.22 18.63 ± 1.87*
Length of apical zone [cm] 6.29 ± 2.10 7.30 ± 0.55
Each value represents the mean ± standard error of 3 replicates. Means with asterisk (*) in the same row are signicantly different
(P ≤ 0.05) according to t-test.
T a b l e 2
Root system architecture (RSA) parameters of cvs. ‘Giza 45’ and ‘Giza 90’ cotton plants (14 days age) measured using EZ-Rhizo
software under 150 mM NaCl salinity stress (Experiment 2)
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Agriculture (Poľnohospodárstvo), 63, 2017 (4): 142−150
149
case of ‘Giza 90’ cultivar, was identied. This low-
cost approach using inexpensive material and open
source software will allow a rapid and cost effec-
tive phenotyping of root systems present in cotton
germplasm available in developing countries. The
obtained results in this work will hopefully open the
door for future studies including additional acces-
sions and salinity levels allowing performing ac-
curate correlation studies between each of the RSA
and salinity tolerance parameters.
Acknowledgments. The authors would like to
thank Professor Dr. Saeed Hamouda for providing
seeds of ‘Giza 90’ and ‘Giza 45’ cotton cultivars and
for his constructive comments on the experiments.
The help of Mohamed Saad and Reham Naguib in
plant analyses is deeply acknowledged. The nan-
cial support for this work was provided by the Fac-
ulty of Agriculture, Cairo University, Egypt.
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