5 days ago PDF | The source-sink relationship and its impact on the yield performance of five hybrid rice varieties (BRRI hybrid dhan3, Heera4. sink relationships, the characteristics of source, sink, flow and grain filling and how to coordinate the source-sink contradictions in super hybrid rice. treatment (rice varieties with source-sink manipulations). The grain yield and .. source relationship in different rice (oryza sativa L.) cultivars,”.
However, environmental influence on total chlorophyll content of flag leaf was relatively small. Comparison of flag leaf chlorophyll content and chlorophyll a: Flag Leaf Photosynthetic Rate Photosynthetic rate of flag leaf at 2, 9, 16, and 23 days after flowering is presented in Table 5. There was no significant difference among the tested hybrid and inbred varieties with respect to flag leaf photosynthetic rates at different days after flowering except at 23 days after flowering.
Photosynthetic rate of flag leaf ranged from The photosynthetic rate gradually decreased with the advance of grain filling period. At 23 days after flowering, Heera2 and BRRI hybrid dhan2 showed significantly higher photosynthetic rate than BRRI dhan45, but the studied hybrid and inbred varieties exhibited decreasing trend of photosynthetic rate of the flag leaf at 9, 16, and 23 days after flowering in all planting dates.
The Heera2 and BRRI hybrid dhan2 showed considerable decrease in flag leaf photosynthetic rate 9 days after flowering in the 5 February planting.Source- Sink Movement
Comparison of flag leaf photosynthetic rate among hybrid and inbred rice varieties at different dates of planting in dryseason, Shoot Reserve Translocation Dry matter accumulation at heading and its remobilization to the grain of the tested hybrid and inbred varieties at four planting dates for two year have been shown in Table 6. Studied hybrids exhibited 7.
Preanthesis dry matter accumulation in shoot and its translocation to the grain of hybrid and inbred rice varieties at different dates of planting in dryseasons, and Leaf Area Index Leaf area index LAI increased gradually in all the tested varieties in all the planting dates up to heading and in most of the cases the differences are nonsignificant.
Source-sink relationships in crop plants 
Thereafter, the reduction of LAI is greater in inbred than that of hybrids Figure 1. As an outcome, the hybrid varieties sustained higher LAI after heading to maturity over inbred BRRI dhan45 regardless of planting dates. Days to heading decreased gradually with delayed planting and the magnitude of reduction was almost similar in the hybrid and inbred varieties.
However, the maximum LAI was recorded from Heera2 6. The maximum value of LAI gradually decreased in hybrid and inbred varieties with delayed transplanting due to reduction of vegetative phase. The leaf area development of studied varieties at different planting dates in was more or less similar to the previous year. This result revealed that hybrid rice varieties maintained significantly greater LAI from heading to maturity stage compared to the inbred.
Leaf area index LAI of hybrid and inbred varieties at different DAT in dry seasons, andrespectively. Vertical bars represent standard error. Arrows indicate start of heading stage.
Source-Sink Relation and Postheading Crop Growth Rate Ratio of spikelets number to leaf area at headingyield sink to leaf area at headingand grain dry matter accumulated from current photosynthetic assimilation to leaf area average from heading to maturity were reflected the source-sink relation in the studied hybrid and inbred varieties Table 6. Inbred BRRI dhan45 exhibited higher ratio of grain dry matter accumulated from current photosynthetic assimilation to leaf area average from heading to maturity compared to both hybrids.
In delayed planting 5 February yield sink per unit leaf area was significantly decreased in tested varieties. Both the studied varieties and the different planting dates showed almost similar trends in postheading crop growth rate as that of yield sink per unit leaf area.
Interaction effect of variety and planting date were nonsignificant in all the cases.
Source-sink relationships in crop plants
These results indicated that BRRI dhan45 has the genotypic superiority over the tested hybrids with respect to postheading photosynthetic assimilation per unit leaf area. Discussion Flag leaf is the main and most active photosynthetic source of grain yield in rice [ 323839 ]. Chlorophyll content indicates photosynthetic efficiency of leaves [ 2440 ].
In the present investigation flag leaf of the tested hybrid varieties contained higher amounts of chlorophyll and maintained higher chlorophyll a: Fluctuation in flag leaf chlorophyll content was small among the different planting dates.
It indicated that higher flag leaf chlorophyll content was the inherent characters of the studied hybrids. In this study there was no significant difference in flag leaf photosynthetic rate between the studied hybrid and inbred rice varieties, irrespective of planting dates.
However, Sinclair and Horie [ 29 ] and Peng et al. Studied hybrid rice varieties showed slightly higher photosynthetic rate in flag leaf at 23 days after flowering. This may be due to the slow senescence of flag leaves and plants of the hybrids. Higher chlorophyll content in the flag leaves and its slow reduction toward maturity delayed senescence of the hybrid rice varieties Table 4.
This observation was partially consistent with Peng et al. Therefore, it seems consistent that higher flag leaf chlorophyll content and chlorophyll a: In early plantings 20 December and 5 Januarystudied rice varieties took longer in the vegetative phase.
Due to vigorous vegetative growth at the middle growth stage, tested hybrid varieties accumulated significantly higher amounts of dry matter at heading over the inbred. Accumulated larger dry matter triggered better assimilate remobilization at the grain filling stage.
A similar result was reported by several other investigators [ 11719204344 ]. Dry matter accumulation was steeper in Heera2 and BRRI hybrid dhan2 at early planting due to the low temperature induced-longer vegetative duration and efficient source activity. That means dry matter accumulation in the studied hybrid varieties before heading was highly thermosensitivity.
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Photosynthetic efficiency of the same genotypes varied markedly during different growth stages [ 4546 ]. The present study suggested accumulation of more dry matter before heading and its higher translocation into the developing grain during filling stage resulting in higher yield of hybrids over the modern inbred.
This result was at par with the findings of Laza et al. The shoot reserve translocation was negatively correlated with the temperature of grain filling period. Hybrid rice varieties exhibited higher degree of sensitivity to temperature rising in regard to shoot reserve remobilization to grain compared to the inbred.
Source-sink relation and postheading crop growth rate of hybrid and inbred rice varieties at different dates of planting in dryseasons, and Relationship between the shoot reserve translocation percentage and average daily temperature from flowering to maturity.
Average data of two dry seasons, and used. In the case of early planting, higher biomass accumulation and rapid expansion of leaf area of the tested hybrids produced higher LAI just after heading and developed an efficient sink large panicles.
This higher leaf area index contributed to the supply of higher amount of photosynthate to the grain at the filling stage and finally contributed to the higher grain yield of hybrid Heera2 and BRRI hybrid dhan2. The ratio of grain dry matter accumulated from current photosynthate to average leaf area from heading to maturity was almost similar in hybrid and inbred rice varieties indicating that leaves other than the flag leaf of studied hybrid rice varieties had the lower photosynthetic capability at grain filling stage than inbred BRRI dhan This situation was aggravated by the rising temperature in delayed plantings.
Besides these, shorter vegetative duration reduced dry matter accumulation and rising temperature impaired shoot reserves translocation. As a consequence, yield of hybrid varieties decreased rapidly compared to the inbred under delayed planting. Both the hybrid varieties showed relatively higher postheading-CGR at early planting due to their higher LAI at the grain filling period.
It might be due to the intrinsic genetic trait or well adaptability of inbred BRRI dhan5 to environmental conditions. These results suggested that modern inbred BRRI dhan45 was efficient in source utilization at the grain filling stage under higher temperature. Grain filling is a deposition of starch from two sources: Grain filling index reflects the source-sink relationship [ 36 ]. Efficient assimilate supply to the grain from the source and the capacity of the sink to receive it determines the higher yield grain filling percentage and these processes depend highly upon environmental conditions [ 4849 ].
In spite of prevailing normal temperature one week before and after of flowering data not shown and normal appearance of spikelets, the number of filled grain as a percentage declined rapidly in studied hybrid varieties than in inbred BRRI dhan45 at delayed planting. This poor filled grain percentage was associated with lower postheading crop growth rate and also related to failure of assimilates supply to the spikelets due to rising temperature.
The photosynthetic rate of flag leaf significantly increased at flowering and then decreased rapidly in delayed planting Table 4. It reveals that translocation of dry matter from shoot to grain was relatively inefficient for hybrids in delayed planting.
This result confirms the findings of Yan et al. Large sink size or sink strength of hybrids creating higher demand for photosynthetic assimilates increased photosynthetic rate in flag leaf initially at delayed planting.
Individual grain weight remained unchanged in hybrids at delayed planting indicating that physiological activity of the sink was not affected significantly due to rising temperature.
However, the studied hybrids were more vulnerable to rising temperature in respect to assimilate translocation to grain than that of the inbred variety. To avoid the adverse effect of higher temperature, the hybrid varieties should be transplanted at the onset of the dry season.
Conclusion It is concluded that the tested hybrid rice varieties accumulate higher amount of dry matter before heading and maintain large LAI at the grain filling period compared to the inbred variety, irrespective of growing temperature. However, relatively high temperature impaired slow rate of remobilization and transportation of assimilates ultimately causes rapid reduction of the percentage of filled grain in the hybrids compared to the inbred variety.
Conflict of Interests The authors declare that there is no conflict of interests regarding the publication of this paper. Therefore, it is necessary to adopt some reasonable cultivating measures to promote source, smooth flow, and increase grain wright for steadily achieving high-yielding cultivating in super rice.
According to Ma Jun [ 27 ]super hybrid rice plants have more vascular bundles with larger areas of each vascular bundle, more total vascular bundles, and greater total phloem and total xylem in the first internode than the ordinary hybrid rice, Shanyou The vascular bundle has a similar spikelet number load and sink load in super hybrid rice and Shanyou 63, though the former has many more spikelets than the latter.
The vascular tissues in super hybrid rice panicles reduce the spikelet number load and sink load. Therefore, the problem to be solved to avoid poor assimilate during grain filling in super hybrid rice cultivars with inter-subspecies heterosis involves both genetic and physical mechanisms [ 2829 ]. Some super hybrid cultivars such as Zhongzheyou 1, Yongyoul2, Yongyou 15, Dyou and Liangyoupeijiu have been planted in Wenzhou, China.
They have not only large panicles but also a higher seed setting rate and grain plumpness. Generally, the superior spikelets fill earlier and faster than the inferior ones, and in addition the inferior ones show an obvious diapause phenomenon in the early period of heading. This paper found significant differences in grain filling characteristics between super hybrid rice Liangyoupeijiu and a large panicle type ordinary hybrid rice Xieyou 46 Figure 1.
The superior spikelets of Xieyou 46 quickly fill to full grain during the initial filling stage, after which the grain weight increases little. Figure 1 presents a line with the same slope in the first stage of grain filling, followed by another line approximately parallel to abscissa tmewith an obvious break point between two lines.
However, the superior spikelets of Liangyoupeijiu rapidly increase in grain weight during the early stage of grain filling, then the rapid growth slows as maximum grain weight is neared.
This is seen with the smaller arc-shaped curve during grain filling. The weight of inferior spikelets of the two cultivars increases much more slowly than that of superior spikelets, and that of Liangyoupeijiu is slower than that of Xieyou The slope of grain filling of inferior spikelets in Liangyoupeijiu is less than that of Xieyou 46, which indicates that there is still insufficient supply of assimilate products in the inferior spikelets of super hybrid rice.
Other researchers also reported similar results [ 34 ]. Therefore, it is crucial to improving the seed setting rate and the grain plumpness degree of inferior spikelets for super hybrid rice high-yielding cultivars. Figure 1 Comparison of grain filling of super hybrid rice cultivar Liangyoupeijiou and conventional hybrid rice cultivar Xieyou 46 in superior 1 and inferior 2 grains.
The super hybrid rice Teyoul75 planted in Taoyuan Town once set a world record of rice yield at that time, but similar production levels have been recorded in Wenzhou. Liangyoupeijiu planted in the plains and low mountains of Wenzhou, China has an outstanding performance, but it is not adaptable to high mountainous areas because of its susceptibility to the false smut occurring in Wenzhou [ 37 ].
Therefore, in order to fully take advantage of the high yield potential of super hybrid and reducing the discrepancy between source and sink, it is important to select excellent cultivars of super hybrid rice and study the characteristics of cultivation such as sensitivity to light, temperature, and feasible date of sowing and transplanting, as better light and temperature environments are required during the filling stage.
For example, the growth period of Liangyoupeijiu is too long for its cultivation as double late rice in Wenzhou, but it is still an appropriate cultivar if sown before June 20, because of its greater thermo sensitivity.
Therefore, it has been planted widely in Wenzhou.
At present, other excellent cultivars such as Zhongzheyou8, Yongyou9 and Zhongzheyoul have been widely planted scale in Wenzhou, as they are the main cultivars with disease resistance, high yield, and high quality [ 38 ].
Stronger seedlings have more tillers and higher root activity, so the plants quickly turn green and develop tillers early after transplantation.
The panicles developed from early emergence tillers or nursery field tillers have well-developed vascular tissues, which improves the transportation of photosynthetic products to grains and increase their source capacity due to higher leaf area and longer vegetable growth duration. Most planting techniques aim to raise stronger seedling by precisely controlling sow seed rate, fertilizer and water management, and chemically regulating the height of seedlings.
It is more difficult to raise stronger seedlings for super hybrid double late rice, because of the longer required nursery period with strong light and high temperatures.
Thin sowing is an important measure to raise stronger seedling for double late rice. In the basal fertilizer applied to seedbeds, nitrogen fertilizers should be decreased while phosphorous and potassium fertilizers increased. Moreover, N fertilizers are usually not applied during the nursery period, except a small amount 3 days before transplanting in double late rice. In Wenzhou, planting super hybrid rice as a single crop can slightly increase the seeding rate when sown between late May and early June, using semi-dry cultivation with a seedling age of about 35 days to ensure enough time for the growth of preceding crops [ 41 ].
It has been shown that the population with high spike rate on the basis of a certain number of spikes is a high photosynthetic efficiency population [ 42 ].
Population with high photosynthetic efficiency possesses high-yielding potential due to several factors including coordination between the the individual and population levels, high light transmittance through leaf layers, organized leaf canopies, low extinction coefficient, high grain-leaf ratio, high photosynthetic efficiency and net assimilation rates [ 43 ].
The early and middle tiller stages are the important periods to set up populations with high photosynthetic efficiency. Maximizing the number of effective tillers requires fertilizer made up of nitrogen and basic manure, as well as early dry-cultivation with multiple light sources [ 44 ]. The application of nitrogen in spikelet-developing fertilizers can increase nitrogen content, increase photosynthetic efficiency, and reduce the degradation of spikelets.
Application of potassium in spikelet developing fertilizers can promote the synthesis and transfer carbohydrates to the grains, increasing seed setting rate and grain plumpness degree [ 47 ]. Exogenous hormones can also regulate the filling of super hybrid rice [ 48 ].