INTRODUCTION
The continuous salinization of arable land is
a threat to global food security. Over 800 Mha of
land are affected by salinity, which equates to more than 6% of the world’s total
land area (FAO 2010) and affects more than 20% of present-day agriculture (Mickelbart et al. 2015). Soil salinity and sodicity assessment of the Middle Awash specifically Amibara Irrigation Project showed that substantial parts of
farm areas affected by salinity problem (Frew et al., 2015; Ashenafi
and Bobe, 2016; Melese et al., 2016). As a result in the area
declining crop production is the most common problem
and some part of Amibara Irrigation Project totally
out of crop production due to soil salinity. Wheat (Triticum aestivum L.) is one of most important
crop plants worldwide with annual production of about 736 million metric tons
(FAO, 2015), but suffers significant grain yield losses due to soil salinity. There
are several strategies to increase wheat production in the salt-affected areas
(such as leaching and drainage), the cultivation of
tolerant genotypes is recognized as the most effective way to overcome this
limitations (Ashraf et al., 2006). The prerequisite is identification of
wheat genotypes with proven wide adaptation under saline conditions. High
concentration of complex inorganic salts present in the growing medium, retard
the growth in most of the crop plants depending on the nature of the salts
present, the growth stages and the salt tolerance or avoidable mechanism of the
plant tissues (Ashraf et al.,2002). Most of the crops tolerate salinity to a
threshold level and above, where yield decreases as the salinity increases
(Khan et al., 2006; Beakal et al.,
2016). Characters such as germination, survival and seedling growth or biomass
accumulation, have been the most commonly used criteria for identifying
salinity tolerance in plants (Khan et al., 2006).
The present study was
carried out with the major objective of providing information on the extent and
basis of genetic variation for salinity tolerance in wheat varieties at germination,
seedling and field stage.
MATERIALS
AND METHOD
Description
of the study area
The study was
conducted from 2014 to 2018 at Amibara District, Werer agricultural research center, located at
9°20’31" N latitude and 40°10’11" E longitude and the elevation is at
about 740 masl. Screening for salt tolerance was
conducted at three growth stages; germination, seedling and reproductive at
laboratory, lath house and saline soil field condition, respectively. The trial
was performed through exposing all wheat varieties to salt stress condition
while selecting relatively tolerant at each growth stage and advancing to next
growth stage. Since large number of genotypes, screening for salinity tolerance
in the field is difficult, due to spatial heterogeneity of soil physico-chemical properties, and difficulty for management
in the field.
Experimental procedures
Germination Test
At germination stage a total of forty six (46) wheat varieties collected
from Melkasa Agricultural Research Center were tested.
Germination stage screening was conducted through subjecting each wheat
varieties to different level of salt concentrations; control (distil water),
10, 20 and 30 dS/m. Saline solutions were prepared
from NaCl. The experimental design was complete
randomized design (CRD) with three replications. Ten seeds of each varieties were placed in petri dish then salt concentrations
were applied. Seeds that produce full radical were considered as germinated.
First germination count was made at 5th day after treatment
application and counting was also done at 7th and 10th
days to take into account late germinated seeds. From recorded data germination
percentage, germination mean time and germination stress tolerance index of
seeds were computed accordingly.
Mean germination time (MGT)
which was calculated according
to the equation
of Ellis and Roberts (1981):
MGT = ΣDn/Σn;
Where: n = number of seeds which were germinated on day D,
D = number of days
counted from the beginning of germination.
Germination Index (GI) which was calculated as described by the Association
of Official Seed Analysts (AOSA, 1983) as:
GI = ∑
(Gt / Tt);
where GI = [Number
of germinated seeds in first count/ Days of first count] +…+ [Number of germinated seeds
in final count/Day of final count).
Seedling stage screening
Seedling stage screening was conducted under lath house condition with
selected varieties under germination stage. Bulk surface soil (non-saline and
alkaline in reaction) was collected and packed into pot. Three salinity levels
(control, 10 and 20 dS/m) of saline solutions were
prepared from NaCl. Treatments were arranged in CRD
with three replications. Ten seeds of each selected varieties were sowed on
pot. Accordingly saline solutions were added to each pot maintaining to field
capacity. Subsequent irrigations were made to a field capacity at five days
interval. Drained solutions collected from each were added again to the
respective experimental pots. Emerged seedlings were counted at 5, 7 and 10
days after planting and expressed as germination percentage, mean germination
time and germination stress index. Shoot and root length, and shoot and root
dry matter were also recorded.
Field Experiments
Screening for salt tolerance and evaluation for yield performance at
field condition was carried out at Werer Agricultural
Research Center experimental site. Before sowing, soil was taken at surface depth (0-30
cm) from the
experimental site, air
dried and sieved
through a 2 mm screen. The soil was analyzed in the laboratory
for some physical and chemical characteristics by standard methods. Laboratory
result showed that the soil of the study had an ECe
of 12-14 ds/m. The treatments were laid out in RCBD with three replications on
a plot size of 3 m x 3 m.
Statistical Analysis
Analysis of variance
(ANOVA) on collected parameters were carried out using
SAS version 9.4 statistical software program (SAS, 2016). Significant
difference among treatment means were assessed using the least significant
difference (LSD) at 0.05 level of probability (Gomez and Gomez, 1984).
RESULT AND DISCUSSION
Germination
stage screening
Germination percentage of all 46 wheat
varieties decreased gradually with increasing salinity levels of the media
(Figure 1). Variation in seed germination was recorded in all the tested wheat
varieties. Mean germination percentage of most varieties were above 85% at 0
ds/m (control) while it decreases at 10 ds/m and 20 ds/m salt levels. When the
salt stress further increased to 30 ds/m in most wheat varieties, the
germination percentage were below 50% (Figure 1d). This might be that, inorganic
salt concentration in the media hinder and delay wheat germination. The same
result reported by Khan et al., (2007) and BIabani et
al., (2013), wheat germination decreased with increasing salinity levels of the
media. Based on the result nine relatively tolerant genotypes (Gambo (v1), Botitho (v2), Tay (v3), Shorima (v4), Meda-wolabu (v5), K-6290 (v6), ETBW – 5879 (v7), Hidassie (v8) and ETBW – 6095 (v9)) with higher germination
percentage were selected and advanced to seedling stage screening.
Plant height and Root
Length
The analysis of variance showed that plant
height and root length of wheat were significantly (P<0.05) influenced due to genetically difference. The
highest plant height observed from K-6290 variety (82.77 cm) followed by Gambo (80.57 cm), while the lowest plant height was
obtained from ETBW-5879 (67.00 cm) and ETBW-6095 (67.42 cm). The highest root
length was observed from Gambo variety (14.23 cm)
followed by Tay # 14 (12.78 cm), while the shortest root length was obtained from Botitho
# 29 (10.76 cm) and Mede-Welabu (11.36 cm). Under
saline conditions, depletion of O2 deprives the plants of its primary energy
source and accumulation of internal ethylene causes the inhibition of root
elongation (Ashraf et al., 2005) by reducing root growth, which consequently
reduce root fresh and dry biomass (Khan et al., 2007).
Tiller
Number
Tillering is one of
the most important agronomic traits because tiller number per plant determines spike
number, a key component of grain yield. Regarding number of tillers per plant
analysis of variance (ANOVA) showed that there was no significant difference
among tested wheat varieties in tiller production at maturity at lath house.
Spike length
The analysis
results revealed that there was variation among tested varieties for spike
length. Gambo variety showed significantly higher
spike length (9.74) than the other wheat varieties, while K 6290 variety showed
lower spike length (7.53) than other nine wheat varieties. Soil salinity directly affects plant growth
through osmotic stress and ionic toxicity caused by Na+, Cl¯ and SO42¯ and thus reduce spike length. Rajpar et al., (2006) reported soil salinity clearly affect spike length of
wheat. Asgari et al., (2011) after screening
four wheat varieties under four salinity levels, reported plant height, spike length, seed number per
spike, root length and grain yield difference among tested wheat varieties due
to salt effect.
Number of spikelet per Spike
Number of seed per spike
showed significant difference among tested varieties. The results presented in
Table 2 show that Tay #14 (42.67) gave higher seed
number per spike, while the lower seed number per spike was obtained from Mede-Welabu (25.56). This experiment revealed that, production
of shorter plants with small and empty spikes might have affected the grain and
straw yield in saline soil treatments, however,
genetic difference to respond for such stress varies among wheat varieties. The
same result reported by Asgari et al., (2011).
Grain Yield
The result
indicates that there was statistically significant variation between tested
wheat varieties for most measured parameters. ETBW-7879 and HIDASIE gave highest grain
yield, while K-6290 and MEDE-WELABU varieties grain yield were appeared
inferior other than tested wheat varieties. Clear different response to saline
stress condition observed among tested materials suggests that existence of
genetic variability among tested materials. The same result
reported by Turki et
al., 2012 salinity induced variations in grain yield and quality were larger
among sensitive genotypes than salt tolerant ones. These results suggested that
breeding and the use of salt-tolerant wheat cultivars might be the most
promising strategies for harvesting higher grain yield of best quality under
saline conditions.
CONCLUSION
The results obtained from this experiment
showed that soil salinity had clear effect on wheat crop at different growth
stage. It was observed that increasing soil salinity progressively
decreased germination percentage, plant height, spike
length, number of spikelet per spike and grain yield. Due to genetic
variability of tested wheat varieties Botitho #29, Tay # 14,
Shorima #
14, Meda-wolabu # 35, K 6290, ETBW – 5879, Hidassie and ETBW- 6095 were relatively showed high
germination percentage. In further screening under saline soil; plant height,
spike length, seed number/spike, root length and grain yield were showed
significant difference among tested wheat varieties. ETBW-7879 and HIDASIE were
the varieties that gave highest grain yield, while K-6290 and MEDE-WELABU
varieties were appeared to be inferior in grain yield other than tested wheat
varieties.
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