Study on the Yield and Yield Contributing Characters of Aus Rice Varieties in Various Soil Moisture Levels ()
1. Introduction
Water deficit is a major problem of growing rice, especially in low rainfall season [1] . According to the IRRI [2] , water deficit is one of the major constraints to rice (Oryza sativa L.). Rice is more susceptible to drought than any other crops. Drought is one of the biggest enemies of Bangladeshi farmers. In 1999, Bangladesh suffered the longest drought in 50 years, with more than four months without rain and in 2010 the country recorded its lowest rainfall since 1995. It is estimated that the world needs to produce 40% more rice to feed the population by 2025 [3] .
Water stress is one of the major abiotic stresses that severely affect and reduce the yield and productivity of rice. It has been identified as the key factor for low productivity in the rain fed ecosystem reported by [4] . [5] found that drought limits productivity and affects both quality and quantity of the yield. [6] found that in the case of rice shoots accumulate proline in water stress conditions. [7] observed that metabolic changes during drought affect reduction of nutrients. [1] stated that drought affected the growth and reduced shoot, root weights, lengths and also physiological processes. Severe water stress may result in the arrest of photosynthesis, disturbance of metabolism and finally the death of plants [8] . Water stress at or before panicle initiation reduces potential spike number and decreases translocation of assimilates to the grains, which results low in grain weight and increases empty grains [9] . [10] found that a significant decrease in panicle number and filled grain per plant, and an increase in the number of unfilled grain were the main causes of sterility percentage increase due to drought treatment [10] . In agriculture, mild to severe drought has been one of the major production limiting factors. The total rainfall in three months is very irregular and often inadequate which fails to meet the evapotranspiration demand. Most of the traditional aus varieties possess quite a good grade of resistance to water stress. That is why the government is thinking about growing crops in more fields in this season. According to [3] , there is an urgent need to increase rice production to meet global demand. Hence, water stress management strategies need to be taken for better yield and improved varieties that are more resilient to abiotic stresses. Agricultural technology related to crop production has to be developed according to specific location. Considering this, the study was undertaken to achieve the following objectives yield contributing characters of aus rice genotypes under water deficit conditions.
2. Materials and Methods
The pot experiment was conducted at the Plant Physiology Laboratory (central laboratory) and also Agricultural research field of Agricultural Botany Department, Sher-e-Bangla Agricultural University, Dhaka-1207, Bangladesh under polythene Shade house condition in controlling the intrusion of rainfall during the period from March to July 2014.
2.1. BRRI Materials
BRRI dhan55 (V1), BR6976-2B-15 (V2) and tolerant check Hashikalmi (V3) were collected from BRRI (Bangladesh Rice Research Institute).
2.2. Methods, Design and Treatment
Seven drought conditions were used as treatments that started from 20 days of seedling age. The pot experiment was done with Randomized Complete Block Design (RCBD). There were seven treatments of water deficiency, three replications, and three genotypes (63 pots) were used. Seven treatments were:
T0 = Throughout the experimental period continuously irrigated (control).
T1 = When the seedlings were 20 days old water deficit imposed for 7 days,
T2 =When the seedlings were 35 days old water deficit imposed for 7 days,
T3 = When the seedlings were 55 days old water deficit imposed for 7 days,
T4 = When the seedlings were 75 days old water deficit imposed for 7 days,
T5 = When the seedlings were 95 days old water deficit imposed for 7 days,
T6 = When the seedlings were 115 days old water deficit imposed for 7 days.
2.3. Seed Cured and Spreading
Uniform size and shape of seeds were cured with Bavistin (5 g in 1/2 liter of water) for 20 minutes. Cured seeds were spreading in the Petridis with water. In March, 2014 sprouted seeds were scattered in pots.
2.4. Pot Filled up and Fertilizer Use
Pots were filled up with 10 kg sandy loam soil. Earthen pots were used of 38 cm × 25 cm in size, sandy and sandy loam. The soil was fertilized 160-150-150 kg urea, triple super phosphate (TSP) and muriate of potash (MP) per hectare, respectively [11] .
2.5. General Observation of the Experiment
Three uniform and vigorous seedlings were permitted to grow in the pots after seedling establishment. For confirming normal growth, the germinated seeds were usually irrigated when the seedlings were 20, 35, 55, 75, 95 and 115 days old water deficit was forced for seven days.
2.6. Detailed Procedures of Recording Data
Data were collected about yield and yield attributing character at maturity stage.
Dry matter
Total dry matter (Figure 1) (root, shoot, panicle etc.) was measured after oven drying for 72 hours at 72˚C.
Weight of 1000-grain
After sun and oven drying thousand cleaned grains weight (g) was calculated with an electronic weighing scale.
Filled and unfilled grain
Filled and unfilled grain was counted up.
Spikelet sterility percentage
Spikelet sterility percentage was recorded from the main stem panicle. The calculation is given below-
Harvest index (HI)
HI is the percentage of grain yield and biological yield [12] . HI was given below
2.7. Data Analysis
All the data were analyzed and the means were separated by DMRT at 5% level of significance using MSTAT-C [13] .
3. Results and Discussions
Objectives were fulfilled by assessing the effects of different duration of water deficit on yield contributing characters of different genotypes. The results of this experiment with necessary discussion are in this chapter.
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Figure 1. Total dry matter (root, shoot, panicle, etc.) of three rice genotypes.
3.1. Leaf Dry Mass
Leaf dry weight was presented in Tables 1-3. There was 0.26 g in V1 followed by 0.25 in V3 and the lowest was 0.23 in V2 in varietal effect. Leaf dry weight under different treatments varied significantly and ranged from 0.17 in T1 and T5 to 0.21 in T0. In the interaction effect of variety and treatment the highest leaf dry weight (0.26 g) was recorded in V1T0 and the lowest weight (0.1267 g) was recorded in V2T1. Water stress significantly decreased plant total dry mass, but the proportion of changes differed among root, stem, and leaf, whereas leaf dry mass decreased [14] .
3.2. 1000-Grains Weight
Weight of thousand grains (g) was shown in Tables 1-3. The highest weight of thousand grains was 16 g recorded in V1 followed by V3 and the lowest weight of thousand grains was 11.67 g in V2 in varietal effect. The highest weight of thousand grains 22.00 (T0) and the lowest weight 14.76 g in T6 In combination effect (variety and treatment) thousand grains 22.66 g in V3T5 and 11.67 g in V1T3.
Weight of a thousand grains was different which depends on the individual grain weight. In this study, BRRI dhan55 and Hashikalmi possess the highest weight of thousand grains.
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Table 1. Varietal effect of leaf dry weight (g) and weight of 1000-grains (g).
Values followed by some letter(s) did not differ significantly at 5% level of probability.
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Table 2. Treatment effect of leaf dry weight (g) and weight of 1000-grains (g).
Values followed by some letter(s) did not differ significantly at 5% level of probability.
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Table 3. Interaction effect of variety and treatments on leaf dry weight (g) and weight of 1000-grains (g).
Values followed by some letter(s) did not differ significantly at 5% level of probability.
Considering the treatment effect the highest weight in T0 and in combination the height weight thousand grains was in V1T0. Under drought conditions BR 6976-2B-15 was mostly source limited during the grain filling stage as a result, grain weight decreased.
The result has infirmity with the results of [15] that showed that weight of 1000 grains was reduced depending on soil moisture levels. [16] showed that water stress after flowering decreased the individual grain weight. [17] advocated that water stress reduced grain weight.
3.3. Number of Spikelets/Panicle
Total number of spikelets/panicles was shown in Tables 4-6. Total number of spikelets was 176.7 in V1 followed by V3 (169.0) and the lowest found 158 (V2). Number of spikelets was highest 158 in T0 and was lowest 139.6 in T1. In combination effect the spikelet 200 in V0T1 and 120 in V3T3.
When photosynthesis became lower, all the spikelets did not get sufficient assimilates, as a result decreased the number of spikelets per panicle. The spikelets recorded highest in BRRI dhan55 (V1). The spikelets found much lower in BR 6976-2B-15. Due to drought stress, the number of spikelets was decreased. After drought conditions the tolerant genotype would quickly recover their biomass, leaves and take no longer time to recover and then develop new growth. The less tolerant genotypes would lose their biomass, leaves and take much longer time to recover. Decreased spikelet’s might be due to inhibition of stomatal conductance, translocation of assimilate to the grains.
3.4. Number of Empty Grains
Number of empty grains/panicles was shown in Tables 4-6. The empty grains/panicle 11 in V3 followed by 10.00 in V2 and the lowest unfilled grain 9.58 inV1. The highest unfilled grain was 12.38 in T0 and the lowest 10.38 in T1. The highest unfilled grain was found at 18.88 in V3T0 and the lowest at 10.27 in V2T3.
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Table 4. Varietal effects on the total number of spikelet’s/panicle, number of unfilled grains per panicle and reduction percent of filled grains.
Values followed by some letter(s) did not differ significantly at 5% level of probability.
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Table 5. Treatment effects on the total number of spikelet’s/panicle, number and reduction % filled grains.
Values followed by some letter(s) did not differ significantly at 5% level of probability.
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Table 6. Interaction effect of variety and treatments on the total number of spikelets/panicle, unfilled grains/panicle and the reduction % filled grains/panicle.
Values followed by some letter(s) did not differ significantly at 5% level of probability.
In this study, it was found that drought stress greatly reduced filled grain and increased the number of unfilled grain. Due to water stress, the current stomatal conductance decreased, as a result the current photosynthesis became lower, insufficient assimilates production was seen and its distribution to grains was insufficient, all the spikelets did not get sufficient assimilates which resulted increased the number of empty grains and decreased the number of filled grains ultimately causes yield losses [15] . The results have the similarity with the results of [16] observed that after flowering increased the number of empty spikelets per panicle under water stress. Before panicle initiation water stress reduces potential spike number and decreases translocation of assimilates to the grains, which results low in grain weight and increases empty grains [9] . [15] stated that under lower soil moisture levels reduced grain yield due to inhibition of photosynthesis and less translocation of assimilates towards grain due to soil moisture stress.
3.5. Reduction Percentage of Filled Grains
Reduction percent of filled grains is in Tables 4-6. The reduction percent of filled grains found 6.51% in V3 followed by 6.33% in V2 and 5.42 in V1. The highest reduction percent filled grain was 8.00 in T6 and the lowest was 6.74 in T4. In combination effect the reduction percent of filled grain 10.97% in V3T4 and the lowest reduction percent filled grain 6.02% in V1T1.
In this study, it was found that the lowest reduction percent of filled grains was 5.42 in BRRI dhan55 (V1) and the highest reduction of filled grain was found in Hashikalmi (V3) and in case of treatment effect the highest reduction percent of filled grains was 7.84, 8.00 in T0, T6 respectively.
Therefore it is suggested that sterility percentage increased with increasing drought duration and number of unfilled grains, decrease in filled grains per plant, tiller number, panicle number, leaf number, plant height. A significant decrease in panicle number and filled grain per plant, increased in number of unfilled grain were the main causes of sterility percentage increase due to drought treatment. These results conform with the results of [10] , who observed increased sterility in rice under water stress conditions. This result also agrees with [16] , who observed that water stress after flowering, increased the number of empty spikelets per panicle. Increased unfilled grains per panicle under lower soil moisture level occurs which decreases translocation of assimilates to the grains, ultimately which results in low gain weight and increases empty grains [9] .
3.6. Total Dry Weight (Root, Shoot and Panicle)/Plant at Harvest
The data on total dry weight per plant (g) was presented in Tables 7-9. In varietal effect the highest dry weight was 64.79 g recorded in V3 followed by 57.08 g in V1 and the lowest weight was 44.82 g in V2. In treatment effect the highest total dry weight per plant was 58.05 recorded in T0 and the lowest was 34.79 in T3.
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Table 7. Varietal effect on total dry weight/plant, harvest index (%) and yield/plant.
Values followed by some letter(s) did not differ significantly at 5% level of probability.
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Table 8. Treatment effect on total dry weight per plant, harvest index (%) and yield/plant.
Values followed by different letter(s) indicate significantly different from each other by DMRT at 5% level.
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Table 9. Interaction effects of variety and treatment on total dry weight per plant, harvest index (%) and yield/plant.
Values followed by some letter(s) did not differ significantly at 5% level of probability.
In combination effect the highest found 65.05 in V1T0 and the lowest found 28.66 in V2T4.
Due to drought stress conditions root, shoot, leaf and panicle dry weight decreased, as a result the total dry matter became lower. In this study, the highest total dry weight per plant was in V1 and V2 and the lowest weight was in V2. This might be due to reduction in tiller number, panicle number and filled grain per plant, plant height, leaf area etc. All of this ultimately affected the grain yield under water stress treatment. The results also agree with the results of [14] who stated that drought stress significantly decreased plant total dry mass, but the proportion of changes differed among root, stem, and leaf, whereas leaf dry mass ratio was decreased. [17] stated that water stress reduced grain weight. [9] observed that water stress at or before panicle initiation reduces potential spike number and decreases translocation of assimilates to the grains, which results low in grain weight and increases empty grains. [15] stated that reduced grain yield under lower soil moisture levels might be due to inhibition of photosynthesis and less translocation of assimilates towards grain due to soil moisture stress. [18] advocated that drought affect rain fed rice systems. Root characteristics such as root length density, root thickness, changes in root dry matter.
3.7. Harvest Index (HI)
The results of harvest index (%) were shown in Tables 7-9. Significant differences found among the varieties and the treatments for harvest index. Harvest index 0.40 was recorded in V1 followed by 0.329 in V3 and the lowest harvest index was found as 0.325 in V2. In treatment effect the highest harvest index 0.40 was recorded in T0 and 0.32 in the T1 treatment. Considering the combination effect, harvest index 0.46 was recorded in V1T0 and 28.66 in V3T3.
In this study, the highest harvest index found was 0.40 in V1 and the lowest harvest index in V2. The results have the similarity with the results that harvest index was significantly influenced by moisture level in all rice genotypes [15] . Where water shortages occurred, harvest index was more conservative than biomass accumulation; harvest index was reduced only when water deficits severely decreased grain-yield [19] .
3.8. Grain Yield per Plant
Yield/plant (g) was shown in Tables 7-9. Yield/plant 23.80 g was recorded in V1 followed by 21.77 g in V3 and 21.33 g in V2. Yield/plant 22.08 g was recorded in T0 control and the lowest yield/plant found as 14.44 g in the treatment T6. In combination effect (variety and drought treatment) the highest yield/plant was found as 23.80 in V1T0 and the lowest yield/plant found 12.20 g in V2T3.
In this study, the highest yield/plant in BRRI dhan55 followed by tolerant check Hashikalmi and the lowest yield/plant in BR 6976-2B-15. The lowest grain yield per plant was recorded in V2 genotypes. The results also have the similarity with the results of [15] who stated that reduced grain yield under lower soil moisture levels. Yield parameters were decreased with the increase of water stress in different growth stages of the crop. As a result of drought, the stomatal conductance and gas exchange were decreased. All of this ultimately affected the grain yield under water stress treatment. The yield components like grain number and grain size were decreased in wheat [20] . Water deficit during vegetative, flowering and grain filling stages reduced grain yield.
4. Conclusion
Hashikalmi and BRRI dhan55 produced the highest number of tillers per plant. It revealed that Hashikalmi showed significantly taller plants throughout the growing period. Hashikalmi produced the largest panicle in all water stress conditions. The largest length of panicle contains more grain which is higher weight than small length of panicle. The grain yield per plant recorded was the highest at control treatment and gradually decreased with increasing water stress duration in the genotypes. But the grain yield was less affected due to water stress treatment compared to others.
Acknowledgements
The authors are grateful to acknowledge SAURES and HEQEP (Higher Education Quality Enhancement Project) for providing financial support to conduct the research work.
Authors’ Contributions
Author HSJ conducted the research work. KUA designed and supervised the study and edited the manuscript. Author HSJ managed the literature searches and JKB collected genotypes from Bangladesh Rice Research Institute.