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Study of water stress effects in different growth stages on yield and yield components of different rice (Oryza sativa L.) cultivars

Hemmatollah Pirdashti 1, Zinolabedin Tahmasebi Sarvestani 1, Ghorbanali Nematzadeh 2 and A. Ismail3

1-Tarbiat Modarres University, Tehran, Iran. Email: pirdasht@yahoo.com;
2
University of Mazandaran, Sari, Iran.;
3
Plant Physiologist, International Rice Research Institute, Manila, Philippines

Abstract

Water stress affects plant growth and development and ultimately, reduces grain yield of irrigated lowland rice. A field experiment was conducted during 2001-2003 to evaluate the effect of water stress on the yield and yield components of four rice cultivars commonly grown in Mazandaran province, Iran. The cultivars used were Tarom, Khazar, Fajr and Nemat. The different water stress conditions were water stress during vegetative, flowering and grain filling stages and well-watered was the control. Water stress at vegetative stage significantly reduced plant height of all cultivars. Water stress at flowering stage had a greater grain yield reduction than water stress at other times. The reduction of grain yield largely resulted from the reduction in fertile panicle and filled grain percentage. Water deficit during vegetative, flowering and grain filling stages reduced mean grain yield by 21%, 50% and 21% on average in comparison to control respectively. The yield advantage of two semidwaf varieties, Fajr and Nemat, were not maintained under drought stress.

Media summary

Water stress affects plant growth and development and ultimately, reduced grain yield of irrigated lowland rice commonly grown in Mazandaran province, Iran.

Key words:

Rice, yield, water stress, grain filling, flowering.

Introduction

Rice (Oryza sativa L.) is the staple food for more than two-third of the world's population (Dowling et al, 1998). About 7.5 % of total rice production comes from irrigated lowland production (Bouman and Tung 2001). It has been estimated that more than 200 million tons of rice are lost every year due to environmental stresses, diseases, and insect pests (Herdt, 1991;Chen and Murata, 2002). Drought stress is a major constraint for about 50% of the world production area of rice. Yield losses from drought in lowland rice can occur when soil water contents drop below saturation (Bouman and Tung 2001). Rice crops are susceptible to drought, which causes large yield losses in many Asian countries (Jearaknogman et al. 1995; Bouman and Tung 2001; Pantuwan et al. 2002), however, some genotypes are more drought resistance than others, out-yielding those exposed to the same degree of water stress. The development of drought resistant cultivars may be assisted if mechanisms of drought resistance are known. In northern Iran irrigated lowland rice usually experiences water deficit during the growing season. Water stress may occur at different growth stages and be of varying duration and intensities, thereby affecting growth and yield. There is very little information on drought resistance of rice genotypes in Iran used in lowland production. This work was carried out to describe the differences in yield of commonly-grown rice cultivars when crops were stressed at different growth stages.

Materials and Methods

A field experiment was carried out in Rice Research Institute of Iran – Deputy of Mazandaran (Amol) located in the north of Iran (52 22َ N, 36 28َ E, altitude 28 m) during 2001-2003. This experiment was laid out to evaluate varietal performance of four rice cultivars in terms of yield and yield components as affected by water stress. The experiment was designed as a split-plot, factorial in a randomized complete block design with three replications. Main-plots were four water stress regimes (water stress in vegetative stage, water stress in flowering stage, water stress in grain filling stage and control or no water stress). The Control was irrigated as required to ensure a high level of standing water throughout crop growth. Plants in water stress treatments were grown under favorable water conditions with supplementary surface irrigation throughout the crop cycle while irrigation was interrupted to induce drought stress at around vegetative, flowering and grain filling stages. Sub-plots were four contrasting cultivars, Tarom, Khazar, Fajr and Nemat. A mixed commercial fertilizer was applied at the rate of 92 kg N ha–1,44 kg P ha-1, and 83 kg K ha-1. Seedlings 30-35 days old were used for transplanting and three seedlings were transplanted to each hill, spaced at 25*25 cm. Plant height was measured on 10 randomly-selected hills by measuring the distance from the soil surface to the tip of the highest panicle within each hill. Grain yield was determined from a harvest area of 4 m2 (64 hills) adjusting to 14% moisture content and yields refer to rough grain yield. All plants from the harvested area were dried at 70 C for total dry matter determination, and harvest index was calculated as grain yield/ total dry matter. Panicle number per m2 was determined at dough stage. To estimate the fertility of panicles, five randomly sampled panicles per plot were counted for filled and unfilled grains and the percentage of filled grains was calculated. Data were analysed by Analysis of Variance. The 2-year data underwent a repeated-measures data analysis by using a combined analysis of variance across years. All statistical tests were carried out using the Statistical Analysis System (SAS Institute 1996).

Results and Discussion

Yield and yield components at different treatments are presented in Tables 1 and 2. Water deficit during vegetative, flowering and grain filling stages reduced mean grain yield by 21%, 50% and 21% respectively in comparison to control. Grain yield differed among the four cultivars. In two years, Nemat had the largest grain yield in the control treatment. When drought stress was imposed at the vegetative stage, the grain yield of Nemat and Khazar and Fajr were significantly reduced. Nemat had the highest reduction (25%), while Tarom and had only a slight reduction (14.5 %). Bouman and Toung (2001) showed that different cultivars might have different responses to the same drought stress timing and intensity. Compared to the well-watered conditions, panicle number was only slightly reduced in Tarom (Table 5).

Grain yield was reduced dramatically in all cultivars with drought starting at panicle initiation or at flowering. Water stress at flowering reduced grain yield more than other water stress treatments. The reduction in yield largely resulted from the reduction in fertile panicle number and filled grain percentage. Chang et al. (1974) reported that in as much as cultivars differ greatly in inherent yielding ability, we could not rely on grain yield difference as the sole criterion of drought resistance. On the other hands, yield losses from the normal level due to water stress are useful in assessing drought resistance. Some researcher reported that grain yield can be drastically reduced if drought occurs during flowering time (Hsiao 1982; Boonjung and Fukai 1996). De Datta et al. (1975), also found that a soil water stress during the vegetative stage reduced grain yields in by an average of 1500 kg/ha; whereas during the reproductive phase, yields were reduced by 2500 kg/ha, or more than 50%. Evaluating the effect of different durations of water stress at various growth stages showed that that water stress at any stage would reduce yield (IRRI 1972). However, the duration of these stresses was more closely related to yield reduction than to stage at which the stress occurred.

Water stress during vegetative stage reduced tiller number, while stress at the reproductive and grain-filling stage reduced grain number and weight. Bouman and Tuong (2001) found that drought before or during tillering reduces the number of tillers and panicle per hill. When late season drought was the main cause of low yield, late-maturity cultivars (such as Nemat) were not suitable as panicle development was severely impaired. Total grain number per panicle was drastically reduced when drought stress occurred at flowering. This reflected the reduced crop growth due to drought during flowering. The proportion of unfilled grain in the drought stress at flowering stage was 46% compared with 22% in well-watered (control) conditions. The 1000-grain weight in the drought stress at grain filling stage was smaller 17% compared to control. Thus, the yield reduction in drought stress at flowering stage mostly resulted from reduction in total grain number per panicle (increase in unfilled grain and a greatly decreased proportion of filled grain) and 1000-grain weight respectively.

It has been argued that under severe drought stress, when yields are reduced to below 50% of those under favorable conditions the relationship between yield under favorable and stress conditions break down (Ceccarelli and Grando 1991). Results of this experiment suggest that genotypes had no capability in expressing their genetic yield potential under these conditions. It appears that the yield advantage observed under favorable conditions of semi-dwarf cultivars (Fajr and Nemat) which required less assimilate for vegetative organs was not maintained under water-limiting conditions.

Table 1: Grain yield and plant parameters of four rice cultivars grown under four water stress treatments in north of Iran.

 

Grain yield A
_____________

Total biomass
_____________

Harvest index
_____________

Plant height
_____________

Cultivar

Water StressB

Year1

Year2

Year1

Year2

Year1

Year2

Year1

Year2

   

Kg ha-1

   

cm

Tarom

W0

4.7ef

4.9fg

12.7b

12.8bc

0.37f

0.38d

154.1a

154.8a

Tarom

W1

4.0h

4.2i

9.5f

9.6f

0.42e

0.44bc

129.16c

129.8b

Tarom

W2

2.5l

2.7l

11.7c

11.8c

0.21l

0.23f

134.6bc

153.2a

Tarom

W3

4.1gh

4.6h

12.1b

12.2c

0.34g

0.38d

132.7bc

153.4a

Khazar

W0

5.5c

5.9c

13.0a

13.1b

0.42de

0.45b

128.9cd

128.6b

Khazar

W1

4.5fg

4.7gh

10.1ef

10.3ef

0.44d

0.45ab

110.9e

111.6d

Khazar

W2

2.6l

2.7l

11.7c

11.7cd

0.22k

0.24f

112.8de

127.8b

Khazar

W3

4.5f

4.7g

11.9bc

12.3c

0.37f

0.38d

109.7e

128.1b

Fajr

W0

6.4b

6.6b

12.9ab

13.4b

0.50a

0.49a

134.8b

117.6c

Fajr

W1

5.0de

5.0f

10.3e

10.4e

0.48b

0.49a

113.2d

99.60e

Fajr

W2

3.2k

3.2l

11.5cd

11.5d

0.28i

0.28e

115.3d

116.0c

Fajr

W3

4.9e

4.9f

11.7c

12.1c

0.42e

0.41cd

110.9e

115.2c

Nemat

W0

7.1a

7.1a

13.7a

15.3a

0.51a

0.47a

131.7c

113cd

Nemat

W1

5.3cd

5.3e

10.8de

10.9de

0.48b

0.49a

109.8e

92.7f

Nemat

W2

3.6i

3.6k

11.8c

11.9c

0.30h

0.30e

110.8e

107.8d

Nemat

W3

5.6c

5.7d

12.1b

12.1c

0.46c

0.47a

110.9e

113.4c

CV (%)

26.83

26.30

9.94

12.28

24.26

22.46

15.12

15.02

Year meanC

4.6

4.8a

11.7a

12.0a

0.39a

0.40a

122.6a

121.1a

AMeans followed by different letters in the same column differ significantly at P=0.05; B W0, control; W1, water stress at vegetative stage; W2, water stress at flowering stage; W3, water stress at grain filling stage; C Means followed by the same letter within rows do not differ significantly at P=0.05.

Table 2: Yield components of four rice cultivars grown under four water stress treatments in north of Iran.

 

Panicle-bearing tiller
________________

Filled grain
_____________

Unfilled grain
_____________

1000 grain wt
_____________

Cultivar

Water StressB

Year1A

Year2

Year1

Year2

Year1

Year2

Year1

Year2

   

No.m-

No. per panicle

g.

Tarom

W0

14.8c

15.5c

91.8b

92.4e

6.9g

6.3i

24.3e

24.7f

Tarom

W1

10.4ef

10.8e

90.6bc

91.2ef

7.5g

8.1i

24.0ef

24.3f

Tarom

W2

14.4c

14.9cd

57.0e

47.9j

18.4f

19.4h

23.3fg

23.7f

Tarom

W3

14.3cd

15.0c

71.4d

71.8c

17.2f

18.0h

21.0h

20.7g

Khazar

W0

12.1de

12.6d

118.9a

119.7b

55.8c

55.4c

30.0bc

30.3b

Khazar

W1

8.86f

9.3e

118.7a

119.3b

56.6c

56.4c

30.0b

30.3b

Khazar

W2

11.1e

11.9de

64.1bc

57.9hi

61.7b

62.5b

29.3c

29.7cd

Khazar

W3

10.5e

10.7e

97.5b

98.1de

75.9a

75.6a

25.0e

25.3e

Fajr

W0

24.3a

25.0a

128.1a

128.4a

30.9e

30.5g

26.7d

26.7de

Fajr

W1

16.8bc

17.8b

126.1a

127.2a

31.6e

31.2g

26.7d

27.0c

Fajr

W2

16.8b

17.3bc

56.6e

64.7h

53.6c

53.7e

26.3d

26.7d

Fajr

W3

16.8b

17.6b

101.2b

101.5d

57.1c

57.7c

22.7g

23.0e

Nemat

W0

24.6a

25.7a

115.5a

116.4b

37.8d

37.5f

32.3a

32.0a

Nemat

W1

18.6b

19.4b

47.8f

114.0g

38.1d

38.4f

32.0a

32.0a

Nemat

W2

18.7b

19.6b

56.6e

57.5i

55.2c

55.2de

30.7b

31.3ab

Nemat

W3

18.7b

18.9b

87.8c

88.1f

64.8b

64.9b

25.0e

25.3de

CV (%)

29.94

30.01

28.89

28.74

50.31

50.13

12.96

12.87

Year meanC

15.7a

16.4a

92.9a

93.5a

41.8a

41.9a

26.8a

27.1a

AMeans followed by different letters in the same column differ significantly at P=0.05; B W0, control; W1, water stress at vegetative stage; W2, water stress at flowering stage; W3, water stress at grain filling stage; C Means followed by the same letter within rows do not differ significantly at P=0.05.

The results also suggest that Tarom is drought-tolerant and is able to retain green leaves longer than other cultivars under drought conditions (data not shown). Retention of green leaves in seedlings under drought conditions has been used as a selection criterion for drought resistance (De Datta et al. 1988). Alternatively, cultivars with green leaf retention may process dehydration-tolerance mechanism which allow the plants to maintain metabolic activity, despite low leaf water potential, for example, as a result of high osmotic adjustment (Fukai and Cooper 1995). Other experiment also confirmed a positive relationship between green-leaf retention and grain yield among 35 lines (Henderson et al. 1995).

From the above results it can be concluded that cultivars required for Iranian conditions, where frequent drought develops, are those with appropriate phenological development to escape late drought, and an ability to maintain growth during drought that may develop late in the season. Consideration of these characters in plant-breeding programs should increase the efficiency of plant improvement in the region.

Acknowledgment

Financial support by the Tarbiat Modarres University and Rice Research Institute of Iran – Deputy of Mazandaran (Amol) highly appreciated.The assistance of Mr. Heshmatollah Pirdashti and Mr. Majid Rahimi on data collection is gratefully acknowledged.

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