IJERD – International Journal of Environmental and Rural Development (2020) 11-1

Research article
erd

Evaluation of Drought Tolerance for Improved Rice Linesin terms of Yield, Chlorophyll content and Water Use
Efficiency
AUNG NAING OO*
Department of Soil and Water Science, Yezin Agricultural University, Myanmar
Email: dr.aungnaingoo@yau.edu.mm

KYAW NGWE
Department of Soil and Water Science, Yezin Agricultural University, Myanmar
Email: dr.kyawngwe@yau.edu.mm

NANG OHN MYINT
Department of Soil and Water Science, Yezin Agricultural University, Myanmar
Email: dr.nangohnmyint@yau.edu.mm
Received 29 January 2020

Accepted 25 March 2020(*Corresponding Author)

Abstract Rice (Oryza sativa L.) is an important target crop for water use reduction becauseof its greater input water requirement than other crops. The pot experiment was conducted toevaluate the effect of two different levels [full irrigation and deficit irrigation (50% Plant
Available Moisture)] on the growth, yield, chlorophyll content and water use efficiency of
improved rice lines. Preliminary test for drought tolerance for the one hundred improved ricelines was conducted and screened under pot experiments in the dry season of 2018. Afterscreening this test, the selected rice lines were grown at two different water levels in thescreen house during the rainy season of 2019. Each experiment was assigned as a randomized
complete block design with three replications at Yezin Agricultural University. The result of
the preliminary test in 2018 found that among the one hundred YAU improved rice lines,
seven lines were tolerant to deficit irrigation. In 2019, all selected rice lines were also tolerant
to deficit irrigation. These lines also produced the best performance of the plant growth, thegrain yield and yield component characters when compared with the checked variety.
However, deficit irrigation for all selected lines reduced these characters when compared withfull irrigation. The five rice lines under deficit irrigation produced the high chlorophyll
content and water use efficiency when compared with full irrigation. Thus, it can beconcluded that the highest drought- tolerant rice lines would be useful for plant breeding
program.
Keywords deficit irrigation, screening rice lines, water use efficiency

INTRODUCTION
Rice (Oryza sativa L.) is the most important food crop for more than half of the population of theworld. It is cultivated over 167 million hectares with the production of 780 million tonnes (FAO
STAT, 2017). It is grown under various environmental conditions in both upland and lowland rainfed
ecosystem. Crop productions are affected by many climatic and environmental factors, which can be
abiotic and biotic factors. Among them, drought is the most significant environmental factor to
impact on the growth and yield of crop in accordance with the global climate change in the world’s
agricultural lands. In Myanmar, especially in the central dry zone areas, rice yield is quite low dueto the salinization, drought, and low soil fertility (Oo et al., 2017). Among them, drought is anincreasingly severe problem in rainfed rice production. To increase crop yield in these areas, it isneeded to study the plant responses to conditions with the ultimate goal of improving crop
performance in areas where water scarcity has a problem. According to further improvement of rice
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breeding program in national level, it offers doing research and providing rice varieties for farmer
needs are recently lined out. The water requirement for rice genotypes vary with different stages of
its establishment processes, and to determine the best tolerance on rice varieties in our country is oneof the advantages and encouraging rice production to climate adaptability.
OBJECTIVESThis study was to evaluate the most drought tolerance rice lines based on the effects of water stresson the growth, yield, chlorophyll content and water use efficiency of improved rice lines.
MATERIALS AND METHODS
Evaluation of Improved Rice Lines at Vegetative StageA population of 100 improved rice genotypes (provided from the Department of Plant Breeding,Physiology and Ecology, Yezin Agricultural University) with Yar-8 (tolerant check) were tested at
the Department of Soil and Water Science, Yezin Agricultural University, Myanmar.
Preliminary test for drought tolerance screening trial was conducted in a net house with 41/23°C
day/night temperatures and a minimum relative humidity of 75% during the day in the dry season of
2018. This trial was laid out in a randomized complete block design with three replications. Twowater levels were used as full irrigation and deficit irrigation (50% Plant Available Moisture). Fivekilograms of 2-mm-sieved air-dried soil was filled in each black plastic pot of 15-cm height and 20cm diameter. Pre-germinated seeds of 100 rice lines were sown at two-three seeds on soil surface ofeach pot. Each plot was well-watered (soil moisture close to the field capacity) before starting the
deficit irrigation which was started at 35 days after sowing. Daily soil water status was monitored byusing soil moisture meter. Fertilizer was applied as the recommended rate of urea, triple
superphosphate and muriate of potash (Buresh and Witt, 2006). Hand weeding and insecticide
spraying were done whenever necessary. Drought tolerance was rated using a modified standard
evaluation system (SES) in rating the visual symptoms of water stress (IRRI, 2013). This scoring
discriminates the susceptible from the tolerant and the moderately tolerant genotypes. Leaf rollingand dry scores were started at 10 days after starting the deficit irrigation.
Evaluation of Selected Improved Rice Lines at Various Stages
This experiment was conducted in a randomized complete block design with three replications in therainy season of 2019. The selected seven rice lines, after screening at vegetative stage, with Yar-8(tolerant check) were grown at two different water levels (full irrigation and deficit irrigation (50%PAM)) in the net house. The black plastic pots (30-cm height and 30-cm diameter) were filled with
twelve kilograms of 2-mm-sieved air-dried fertilized soil. Three to four pre-germinated seeds of test
entries were placed on soil surface of each pot. Two weeks after seeding, seedlings were thinned to
one per pot. Maintain soil water status daily and protect the plants from any pests and diseases were
performed. Fertilizer was applied as the recommended rate. Plant height (cm), the number of tillers
per hill, the number of panicles per hill, the number of spikelets per panicle, filled grain percent,
1000-grain weight, dry matter and grain yield were recorded at harvesting. Chlorophyll content wasmeasured by using chlorophyll meter (SPAD-502, Minolta, Japan) at vegetative and panicle initiation
stages. Water use efficiency was calculated as grain yield (usually the economic yield) divided bywater used to produce yield consumed by the crop during the growing season (Boutraa, 2010). In
order to identify the drought tolerant rice lines, drought susceptibility index (DSI) (Fischer andMaurer, 1978), stress tolerance (TOL) (Rosielle and Hamblin, 1981), mean productivity (MP)(Hosssain et al., 1990), stress tolerance index (STI) (Fernandez, 1992), yield index (YI) (Lin et al.,1986) were also taken into consideration.

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Data Analysis
The collected data were examined statistically using Analysis of Variance (ANOVA) Techniques,
and means were compared by least significant difference (LSD) method at 5% level of probability.
All statistical analyses were done using Statistix 8.0 software and Excel program (2010).
RESULTS AND DISCUSSION
Evaluation of Improved Rice Lines to Drought Stress at Vegetative StageAll one hundred improved rice lines were grown strongly and showed uniform green colour underboth soil water levels. According to the leaf rolling and dry scores, the rice lines differed significantly
for drought tolerance at vegetative stage among the rice lines ranging from score 0 (highly tolerant)
and score 9 (highly susceptible) under deficit irrigation (data not shown).
The one hundred improved rice lines were classified into five groups from highly tolerant (score0) to highly sensitive (score 9) as 0 (highly tolerant), 10 (tolerant), 20 (moderately tolerant), 16(sensitive) and 54 (highly sensitive) at vegetative stage. The effects of water stress on rice plants
were complex and it was difficult to interpret the results. Hence, the selected seven rice lines fromten tolerant lines were evaluated for all stages in the net house.
Evaluation of Selected Improved Rice Lines to Drought Stress
Mean comparisons of selected improved rice lines in terms of plant height and number of tillers perhill under two different irrigation levels at harvesting are shown in (Table 1). The plant height wassignificantly different among the rice lines under deficit irrigation, whereas it was not different infull irrigation. The number of tillers per hill was not significantly different among the rice lines underfull irrigation, while it was significantly different under deficit irrigation at 5% level. Similarly, thenumber of panicles per hill was not significantly different among the rice lines under full irrigation,
whereas it was significantly different under deficit irrigation (Table 2). YAU-1211-82-1-1 and YAU1211-118-1-1 had the highest (16.7 and 15.7) values, respectively. The number of spikelets per
panicle was significantly different among the rice lines under full irrigation at 1 % level. In contrast,
it was not significantly different under deficit irrigation (Table 2).
Table 1 Mean comparison of plant height and number of tillers per hillin different improved rice lines at harvesting
Improved rice lines
YAU-1211-14-1-1
YAU-1201-90-2-4
YAU-1211-118-1-1
YAU-1211-195-1-1
YAU-1201-26-1-1
YAU-1201-26-1-3
YAU-1211-82-1-1
Yar-8 (Tolerance check)F-testC.V %Plant height
(cm)
FI
DI
118.5
105.0 b128.5
97.1 bc
125.3
90.5 c121.5
100.5 bc
126.7
101.6 bc
124.2
104.7 b117.5
106.7 b127.6
119.3 a
ns
**
5.2
6.2

D (%)
8.8
24.5
27.7
17.3
21.9
15.7
11.7
8.2

Number of tillers
per hillFIDI
20.0
11.3 d20.3
13.3 bcd
17.7
16.3 ab
17.0
15.0 abc
13.7
13.3 cd
17.0
13.0 bcd
19.0
17.0 a17.7
15.3 abc
ns
*
21.6
13.7

D (%)
30.0
34.4
7.5
11.8
2.4
23.5
10.5
13.2

Values in the same column followed by the same letter are not significantly different at the 5% level by the LSD test,(**) significantly different at P≤0.01, (*) significantly different at P≤0.05, ns − not significant,
FI: Full Irrigation, DI: Deficit Irrigation, D (%): Percentage decrease down

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The data regarding filled grain percent and 1000-grain weight of selected improved rice lines
under two different irrigation levels at harvesting are presented in Table (3). There was significant
difference in filled grain percent under full and deficit irrigation at 5 % and 1 % level, respectively.
YAU-1211-195-1-1 had the highest filled grain percent (79.1) among the rice lines. The filled grain
percent of this rice line under full irrigation was lower than that under deficit irrigation. 1000-grain
weight was significantly different among the rice lines under full irrigation at 1 % level, while it was
not different under deficit irrigation.
Table 2 Mean comparisons of number of panicles per hill and number of spikelets
per panicle in different improved rice lines at harvesting
Improved rice lines
YAU-1211-14-1-1
YAU-1201-90-2-4
YAU-1211-118-1-1
YAU-1211-195-1-1
YAU-1201-26-1-1
YAU-1201-26-1-3
YAU-1211-82-1-1
Yar-8 (Tolerance check)F-testC.V %Number of panicles
per hillFIDI
17.0
10.7 cd
19.3
9.7 d
17.3
15.7 a16.0
14.0 abc
12.3
12.0 bcd
15.7
10.7 cd
17.0
16.7 a16.3
15.0 ab
ns
*
19.8
15.0

D (%)
29.4
50.0
9.6
12.5
2.7
31.9
2.0
24.0

Number of spikelets
per panicleFIDI
169 ab
124
123 d
121
161 bc111
149 bc131
142 cd
106
189 a
125
154 bc118
186 abc
122
**
ns
8.9
10.8

D (%)
23.9
1.1
31.3
12.7
25.7
33.8
24.1
21.2

Values in the same column followed by the same letter are not significantly different at the 5% level by the LSD test,(**) significantly different at P≤0.01, (*) significantly different at P≤0.05, ns − not significant
FI: Full Irrigation, DI: Deficit Irrigation, D (%): Percentage decrease down

Table 3 Mean comparisons of filled grain percentage and 1000-grain weightin different improved rice lines at harvesting
Improved rice lines
YAU-1211-14-1-1
YAU-1201-90-2-4
YAU-1211-118-1-1
YAU-1211-195-1-1
YAU-1201-26-1-1
YAU-1201-26-1-3
YAU-1211-82-1-1
Yar-8 (Tolerance check)F-testC.V %Filled grain (%)
FI
80.9 ab85.7 a79.5 ab77.2 b85.6 a69.7 c85.1 a73.7 ab
*
5.2

D (%)

DI
68.5 bc
72.5 abc
76.4 ab79.1 a75.3 abc
58.0 d64.9 cd
76.6 ab
**
8.4

15.4
15.4
4.0
-2.4
12.0
16.8
23.6
5.4

1000-grain weight (g)FIDI
25.5 d24.4
31.7 a28.9
28.2 bc
25.7
24.7 d24.7
28.8 b
28.6
26.5 cd
25.8
29.2 b
25.2
29.5 b
25.5
**
ns
4.4
7.4

D (%)
4.1
9.0
8.7
0.2
0.6
2.5
13.9
13.7

Values in the same column followed by the same letter are not significantly different at the 5% level by the LSD test,(**) significantly different at P≤0.01, (*) significantly different at P≤0.05, ns − not significant
FI: Full Irrigation, DI: Deficit Irrigation, D (%): Percentage decrease down

In comparing the seven improved rice lines, the effect of drought stress on grain yield wassignificantly different under deficit irrigation, whereas it was not different under full irrigation (Table4). Yar-8 (Tolerance check) had the highest grain yield (38.8 g) than the rice lines and followed by
YAU-1211-195-1-1 which had the highest grain yield (35.4 g) among the rice lines. In contrast,
YAU-1201-26-1-3 had the lowest yield (19.9 g).
The evaluation of drought tolerant promising rice lines based on a single criterion index wasincongruous (Table 4). Lower DSI and TOL values indicated the more resistant to drought (Winteret al., 1988; Rosielle and Hamblin, 1981). In this study, regarding to DSI and TOL values, YAU1211-195-1-1 and YAU-1201-26-1-1 were the most drought tolerant rice lines, while YAU-1201Ⓒ ISERD28

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90-2-4 and YAU-1211-82-1-1 were the least relative tolerant lines. According to MP, YAU-1211118-1-1 was the most tolerant rice lines, while YAU-1201-26-1-1 was the least rice lines. Concerning
to STI, YAU-1211-118-1-1 was the best tolerant rice lines, whereas YAU-1201-26-1-3 was the worst
relatively tolerant lines. Regarding to YI, YAU-1211-195-1-1 was the greatest tolerant rice lines,
while YAU-1201-26-1-3 was the poorest relatively drought tolerant lines.
Table 4 Evaluation of improved rice lines based on drought tolerance indices
Improved rice lines
YAU-1211-14-1-1
YAU-1201-90-2-4
YAU-1211-118-1-1
YAU-1211-195-1-1
YAU-1201-26-1-1
YAU-1201-26-1-3
YAU-1211-82-1-1
Yar-8 (Tolerance check)F-testC.V %Grain Yield(g per hill)
FI
DI
58.9
25.3 de63.9
24.5 de63.4
33.2 abc
45.3
35.4 ab
41.7
29.3 bcd
54.4
19.9 e66.2
27.2 cd
66.6
38.8 a
ns
**
22.8
10.4

D (%)

DSI

TOL

MP

STI

YI

57.1
59.7
47.7
22.0
29.7
63.5
58.9
41.7

1.17
1.27
0.98
0.45
0.61
1.29
1.20
0.85

33.60
36.21
30.26
9.99
12.40
34.57
38.99
27.72

42.09
42.59
48.28
40.35
35.49
37.13
46.74
52.69

0.46
0.45
0.64
0.49
0.37
0.33
0.55
0.79

0.44
0.43
0.58
0.62
0.51
0.35
0.48
0.68

Values in the same column followed by the same letter are not significantly different at the 5% level by the LSD test,(**) significantly different at P≤0.01, ns − not significant,
FI: Full Irrigation, DI: Deficit Irrigation, D (%): Percentage decrease down

Table 5 Mean comparisons of chlorophyll content (SPAD reading) in different improved ricelines at vegetative and panicle initiation stage
Improved rice lines
YAU-1211-14-1-1
YAU-1201-90-2-4
YAU-1211-118-1-1
YAU-1211-195-1-1
YAU-1201-26-1-1
YAU-1201-26-1-3
YAU-1211-82-1-1
Yar-8 (Tolerance check)F-testC.V %Chlorophyll content
at vegetative stage
FI
DI
39.8
47.2
41.1
44.1
46.1
46.7
40.0
47.0
35.5
44.0
39.9
43.2
42.8
45.3
42.2
44.4
**
ns
5.1
5.5

D (%)
-18.6
-7.2
-1.3
-17.4
-24.0
-8.1
-5.8
-5.1

Chlorophyll content
at panicle initiation
FI
DI
38.9
39.6
33.3
40.6
42.5
39.7
34.8
41.8
30.7
37.2
31.4
39.6
37.9
39.3
36.1
39.7
**
ns
6.2
19.4

D (%)
-1.6
-21.9
6.6
-15.0
-21.3
-26.1
-3.6
-10.0

Values in the same column followed by the same letter are not significantly different at the 5% level by the LSD test,(**) significantly different at P≤0.01, ns − not significant
FI: Full Irrigation, DI: Deficit Irrigation, D (%): Percentage decrease down

The effect of drought stress on chlorophyll content was significantly different under full
irrigation among the improved rice lines, while it was not different under deficit irrigation for bothvegetative and panicle initiation stages. In comparing between two irrigations, chlorophyll content
of the most rice lines resulted from deficit irrigation was higher than that from full irrigation,
indicating that drought tolerant lines had a high chlorophyll concentration. Kalaji et al. (2016) statedthat chlorophyll content was increased in abiotic stress tolerant crops, although it was reduced instress susceptible crops. YAU-1211-195-1-1 had the highest chlorophyll content among the rice lines
under deficit irrigation and followed by YAU-1201-90-2-4 rice line.
Mean comparisons of selected improved rice lines in terms of dry matter production and water
use efficiency under two different irrigation levels at harvesting are presented in (Table 6). The resultⒸ ISERD

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showed that there were significant differences in dry matter production among the rice lines underboth irrigations. In comparing the seven improved rice lines, there was significant difference in WUE
under deficit irrigation, whereas it was not different under full irrigation. WUE ranged from 0.42 kg
m-3 to 0.75 kg m-3. The maximum WUE value (0.75 kg m-3) was found from Yar-8 (Tolerance check)and it was followed by YAU-1201-26-1-1 and YAU-1211-195-1-1, (0.69 kg m-3 and 0.68 kg m-3,
respectively) under deficit irrigation.
Table 6 Mean comparisons of dry matter production and water use efficiency (WUE)
in different improved rice lines at harvesting
Improved rice lines
YAU-1211-14-1-1
YAU-1201-90-2-4
YAU-1211-118-1-1
YAU-1211-195-1-1
YAU-1201-26-1-1
YAU-1201-26-1-3
YAU-1211-82-1-1
Yar-8 (Tolerance check)F-testC.V %Dry matter (g)FIDI
125.7 abc
70.2 d160.6 a72.9 cd139.4 ab78.9 bcd
110.3 bc
80.0 abcd
91.0 c85.3 abc
128.7 abc
84.8 abc
171.7 a87.1 ab146.1 ab92.4 a
*
*
20.3
9.2

D (%)
26.3
25.7
23.7
24.0
26.7
22.7
27.3
24.0

WUE (kg m-3)
FI
DI
0.62
0.42 d
0.67
0.59 abcd
0.67
0.63 abc
0.48
0.68 ab
0.44
0.69 ab
0.57
0.45 cd
0.69
0.53 bcd
0.70
0.75 a
ns
*
22.2
19.2

D (%)
32.5
12.6
6.2
-42.6
-57.3
21.8
23.9
-6.1

Values in the same column followed by the same letter are not significantly different at the 5% level by the LSD test,(*) significantly different at P≤0.05, ns − not significant, FI: Full Irrigation, DI: Deficit Irrigation, D (%): decrease
down

CONCLUSIONSIn conclusion, differences of the selected improved rice lines were observed for relative droughttolerance in terms of growth, grain yield, chlorophyll content and water use efficiency. From thisstudy, five tolerant rice lines would be useful in the areas where drought has a problem.
ACKNOWLEDGEMENTS
The authors would like to thank the JICA (Japan International Cooperation Agency), Project for
Capacity Development of Yezin Agricultural University, for financial support.
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