Super Rice Cultivars Research Articles

Identification of photosynthetic parameters for superior yield of two super hybrid rice varieties: A cross-scale study from leaf to canopy.

Enhancing photosynthetic capacity is widely accepted as critical to advancing crop yield. Therefore, identifying photosynthetic parameters positively related to biomass accumulation in elite cultivars is the major focus of current rice research. In this work, we assessed leaf photosynthetic performance, canopy photosynthesis, and yield attributes of super hybrid rice cultivars Y-liangyou 3218 (YLY3218) and Y-liangyou 5867 (YLY5867) at tillering stage and flowering stage, using inbred super rice cultivars Zhendao11(ZD11) and Nanjing 9108 (NJ9108) as control. A diurnal canopy photosynthesis model was applied to estimate the influence of key environmental factors, canopy attributes, and canopy nitrogen status on daily aboveground biomass increment (AMDAY). Results showed that primarily the light-saturated photosynthetic rate at tillering stage contributed to the advancing yield and biomass of super hybrid rice in comparison to inbred super rice, and the light-saturated photosynthetic rate between them was similar at flowering stage. At tillering stage, the higher CO2 diffusion capacity, together with higher biochemical capacity (i.e., maximum carboxylation rate of Rubisco, maximum electron transport rate (J max), and triose phosphate utilization rate) favored leaf photosynthesis of super hybrid rice. Similarly, AMDAY in super hybrid rice was higher than inbred super rice at tillering stage, and comparable at flowering stage partially due to increased canopy nitrogen concentration (SLNave) of inbred super rice. At tillering stage, model simulation revealed that replacement of J max and g m in inbred super rice by super hybrid rice always had a positive effect on AMDAY, and the averaged AMDAY increment was 5.7% and 3.4%, respectively. Simultaneously, the 20% enhancement of total canopy nitrogen concentration through the improvement of SLNave (TNC-SLNave) resulted in the highest AMDAY across cultivars, with an average increase of 11.2%. In conclusion, the advancing yield performance of YLY3218 and YLY5867 was due to the higher J max and g m at tillering stage, and TCN-SLNave is a promising target for future super rice breeding programs.

A vital option for food security and greenhouse gases mitigation: planting elite super rice in double- to single-rice cropping fields in China

Double-rice cropping (DRC) in southern China has made outstanding contributions to ensuring food security, along with a large amount of greenhouse gas (GHG) emissions. The observed significant shift from double- to single-rice (DtS) cropping since 1990 in southern China has led to great concerns on food security, despite its contribution to GHG emissions reduction. How to ensure food security without compromising the goal of mitigating GHG emission requires innovative thinking and a comprehensive tradeoff analysis of all plausible options. This study adopts a multi-model coupling method to simulate the yield and GHG emissions trade-offs across grid-cells by incorporating the option of planting elite super rice in the DtS areas. The simulation results indicate that planting elite super rice with longer growth period in the DtS areas has the potential to compensate the annual yield loss caused by the DtS shift while significantly mitigating GHG emissions in comparison with the conventional DRC. In more detail, while the yield and GHG emissions of prevailing single-rice cropping are 48% (±2%) and 54% (±4%) lower than the corresponding (two-season sums) figures of conventional DRC under the current irrigation practice of midseason drainage, the yield and GHG emissions of super rice are 15% (±4%) and 44% (±6%) lower than the above reference figures if the emerging irrigation regime of alternate wetting and drying is adopted. Furthermore, our modeling simulations demonstrate the feasibility of promoting elite super rice cultivars across southern China. The research suggests a viable option for China to balance the trade-off between food security and GHG mitigation.

OsPDCD5 negatively regulates plant architecture and grain yield in rice

Plant architecture is an important agronomic trait that affects crop yield. Here, we report that a gene involved in programmed cell death, OsPDCD5, negatively regulates plant architecture and grain yield in rice. We used the CRISPR/Cas9 system to introduce loss-of-function mutations into OsPDCD5 in 11 rice cultivars. Targeted mutagenesis of OsPDCD5 enhanced grain yield and improved plant architecture by increasing plant height and optimizing panicle type and grain shape. Transcriptome analysis showed that OsPDCD5 knockout affected auxin biosynthesis, as well as the gibberellin and cytokinin biosynthesis and signaling pathways. OsPDCD5 interacted directly with OsAGAP, and OsAGAP positively regulated plant architecture and grain yield in rice. Collectively, these findings demonstrate that OsPDCD5 is a promising candidate gene for breeding super rice cultivars with increased yield potential and superior quality.

Lodging Resistance Related to Root Traits for Mechanized Wet-Seeding of Two Super Rice Cultivars

Mechanical hill wet-seeded rice machine is beneficial for establishing and growing uniform rows of seedlings. However, there is limited knowledge regarding the effects of the establishment of furrows on growth, lodging and yield, and their relationships with root traits. In this study, field experiments were conducted during 2012 and 2013 using two super rice varieties (hybrid rice Peizataifeng and inbred rice Yuxiangyouzhan) under three furrow establishment treatments (T1, both water and seed furrows were established by the machine; T2, only seed furrows were established by the machine; and T3, neither water nor seed furrows were established by the machine). Lodging index, lodging-related traits, grain yield, above-ground dry weight and root traits were measured. The results showed that the lodging index was significantly affected by the treatments with furrows (T1 and T2). The strongest lodging resistance was detected in the mechanical hill wet-seeded rice with furrow treatment (T1) in both 2012 and 2013. Lodging resistance was strongly related to the breaking resistance. No significant difference was found in grain yield or dry weight of the mechanical hill wet-seeded rice. Therefore, the mechanical hill wet-seeded rice with furrow treatment increased rice lodging resistance, which was related to root traits.

SNP-based QTL mapping for panicle traits in the japonica super rice cultivar Liaoxing 1

Panicle traits directly associated with yield are a target of selection in rice breeding. Although abundant QTL for panicle traits have been identified, there is little information about the genetic basis of panicle traits in japonica super rice (JSR) cultivars. In this study, we identified QTL for panicle traits in three environments using a population of recombinant inbred lines (RILs) derived from the JSR cultivar Liaoxing 1. A total of 197 RILs were genotyped with 285 polymorphic SNP markers. Phenotypic data and best linear unbiased prediction (BLUP) value of primary branch number (BNP), secondary branch number (BNS), grain number on primary branch (GNP), grain number on secondary branch (GNS), grain number per panicle (GN), panicle length (PL) and grain density (GD) were used for QTL mapping. A total of 105 QTL for seven panicle traits were detected in single environments using their BLUP values. Individual QTL explained 0.51%–52.22% of the phenotypic variation. Of the 105, 49 were also detected by joint multi-environment analyses. Five stable QTL: qGD9, qPL9, qGNP9, qGN6, and qBNS6.2 were identified in multiple environments. qGD9, qGNP9, and qPL9, co-localizing on chromosome 9, likely correspond to the known gene DEP1. Importantly, qGN6 and qBNS6.2 in a co-localization region were identified as novel QTL, and their Liaoxing 1 alleles had a positive effect. Several RILs with the QTL allele combinations qGD9/qPL9/qGNP9 and qGN6/qBNS6.2 showed greater GN. Further investigation of the putative gene underlying qGN6/qBNS6.2 would shed light on the molecular mechanism of JSR.

Higher Radiation Use Efficiency Produces Greater Biomass Before Heading and Grain Yield in Super Hybrid Rice

To reveal the physiological mechanism underlying the yield advantage of super hybrid rice compared with inbred super rice, a super hybrid rice cultivar Yliangyou 3218 (YLY) and an inbred super rice cultivar Zhendao 11 (ZD) were field grown under five nitrogen (N) fertilizer rates in 2016 and 2017. The average grain yield of YLY across nitrogen fertilizer rates was 10.1 t ha−1 in 2016 and 9.7 t ha−1 in 2017, 29.6% and 21.3% higher than that of ZD in 2016 and 2017, respectively. YLY showed higher above-ground biomass accumulation, especially growth before heading, which was mainly due to its faster green leaf area index (GLAI) formation and greater maximum GLAI (GLAImax). The daily radiation interception (RIdaily) was 15.0% higher in YLY than ZD, but the accumulated radiation interception (RIacc) before heading showed little difference between them because ZD had a longer growth duration. The radiation use efficiency (RUE) of YLY before heading was 54.7% higher than that of ZD (YLY, 2.12 g MJ−1; ZD, 1.37 g MJ−1). Our result demonstrated that the yield advantage of YLY was due to its higher above-ground biomass before heading, which was mainly achieved by its improvement in RUE rather than radiation interception.

Structural development and physicochemical properties of starch in caryopsis of super rice with different types of panicle

BackgroundStarch is the main storage substance in rice caryopsis and its properties will determine the quality of rice. Super rice has been extensively studied due to its high-yield characteristics, but the knowledge of amyloplast development and starch quality in caryopsis of super rice especially with large panicle is limited.ResultsTo address this, large panicle typed and normal panicle typed super rice cultivar Yongyou2640 (YY2640) and Nangeng9108 (NG9108) were investigated in this study. The development of amyloplast in YY2640 caryopsis was better than NG9108, showing faster degradation rate of pericarp amyloplast and better filling degree of endosperm amyloplast. Meanwhile, the starch granule of YY2640 presented as polyhedral shape with smooth surface and the granule size was slightly larger than NG9108. The starch of YY2640 exhibited the lower amylose content, ratio of amylose to amylopectin and the higher level of amylopectin short and long branch-chains compared with NG9108, but there was no significant difference in amylopectin branching degree between them. Two rice starches both showed the characteristics of A-type crystal, and the relative crystallinity and external ordered degree of YY2640 starch were higher than those of NG9108. Furthermore, YY2640 starch showed better pasting properties with lower pasting temperature, shorter pasting time, higher peak viscosity, trough viscosity, breakdown value and lower setback value because of lower apparent amylose content.ConclusionsOverall, the development and filling of amyloplast in YY2640 caryopsis were better than those of NG9108, thus leading to better starch quality of YY2640.

High nitrogen input causes poor grain filling of spikelets at the panicle base of super hybrid rice

It is generally accepted that poor grain filling of rice plants under high nitrogen (N) input is due to increased competition for assimilates because high N rate usually results in large sink size with more spikelets per panicle. In this study, we examined grain filling parameters of spikelets in different panicle position under various N treatments to determine the effect of N rates on grain filling. A super rice cultivar with large panicle was grown under field conditions in Wuxue County, Hubei Province, central China in 2013 and 2014. Fully filled spikelet percentage measured at the crop level from 12 hills decreased by 10.9% when the total N rate increased from 0 to 250 kg ha−1, whereas spikelets per panicle remained almost constant across the N rates. At the individual panicle level, reduction in grain filling was evidenced by decreased fully filled spikelet percentage, fertilized spikelet weight, and grain plumpness, and increased partially filled spikelet percentage in the bottom part of the panicle as total N rates increased. Reduction in these grain filling parameters under high N input was relatively small in the middle part of the panicle and was not appeared in the top part of the panicle. Furthermore, high N rates at both mid-tillering and panicle initiation reduced fertilized spikelet weight in the bottom part of the panicle without an increase in spikelets per panicle. Our results suggest that the spikelets in the bottom part of the panicle were mainly responsible for poor grain filling under high N input and such high N-induced poor grain filling was not due to increased spikelets per panicle.

Responses of plant growth, physiological, gas exchange parameters of super and non-super rice to rhizosphere temperature at the tillering stage

Temperature is one of the critical factors affecting rice growth and yield production. This study investigated the effects of rhizosphere temperature at the tillering stage on the growth, physiological parameters and gas exchange attributes of two rice cultivars, i.e., the super rice cultivar Yuxiangyouzhan and the non-super rice cultivar Xiangyaxiangzhan, under hydroponic conditions. Three rhizosphere temperature treatments, i.e., a low-rhizosphere-temperature treatment (LT, nutrient solution at 17.5 ± 1.5 °C), an ambient-temperature treatment (AT, nutrient solution at 27.5 ± 1.5 °C), and a high-rhizosphere-temperature treatment (HT, nutrient solution at 37.5 ± 1.5 °C), were applied in this study. The results showed significant differences in most of the rice growth and physiological and gas exchange parameters as a result of cultivar and rhizosphere temperature as well as their interaction. In addition, the marked reduction in total dry weight was positively correlated with a notable reduction in plant morphological parameters, such as the fresh and dry weight of the leaves and stem sheaths, and changes in gas exchange parameters. Moreover, antioxidant reactions were active in response to high and low rhizosphere temperatures, which varied in different plant tissues. These results suggested that the super and non-super rice were sensitive to high and low rhizosphere temperatures, respectively.

Combined effect of shading time and nitrogen level on grain filling and grain quality in japonica super rice

There is limited information about the combined effect of shading time and nitrogen (N) on grain filling and quality of rice. Therefore, two japonica super rice cultivars, Nanjing 44 and Ningjing 3, were used to study the effect of shading time and N level on the characteristics of rice panicle and grain filling as well as the corresponding yield and quality. At a low N level (150 kg N ha−1, 150N), grain yield decreased (by 21.07–26.07%) under the treatment of 20 days of shading before heading (BH) compared with the no shading (NS) treatment. These decreases occurred because of shortened panicle length, decreased number of primary and secondary branches, as well as the grain number and weight per panicle. At 150N, in the treatment of 20 days of shading after heading (AH), grain yield also decreased (by 9.46–10.60%) due to the lower grain weight per panicle. The interaction of shading and N level had a significant effect on the number of primary and secondary branches. A high level of N (300 kg N ha−1, 300N) could offset the negative effect of shading on the number of secondary branches and grain weight per panicle, and consequently increased the grain yield in both shading treatments. In superior grains, compared with 150N NS, the time to reach 99% of the grain weight (T99) was shortened by 1.6 to 1.7 days, and the grain weight was decreased by 4.18–5.91% in 150N BH. In 150N AH, the grain weight was 13.39–13.92% lower than that in 150N NS due to the slow mean and the maximum grain-filling rate (GRmean and GRmax). In inferior grains, grain weight and GRmean had a tendency of 150N NS>150N BH>150N AH. Under shaded conditions, 300N decreased the grain weight due to lower GRmean both in superior and inferior grains. Compared with 150N NS, the milling and appearance qualities as well as eating and cooking quality were all decreased in 150N BH and 150N AH. Shading with the high level of 300N improved the milling quality and decreased the number of chalky rice kernels, but the eating and cooking quality was reduced with increased chalky area and overall chalkiness. Therefore, in the case of short term shading, appropriate N fertilizer could be used to improve the yield and milling quality of rice, but limited application of N fertilizer is recommended to achieve good eating and cooking quality of rice.

Different characteristics of nutrient absorption and utilization between inbred japonica super rice and inter-sub-specific hybrid super rice

Although previous researchers have revealed that inter-sub-specific hybrid rice between indica and japonica has super-high yield potential, the mechanisms underlying nutrient absorption and utilization remain limited. The present study assessed nutrient accumulation and utilization, root morphology, and physiology of inter-sub-specific hybrid super rice cultivars (IHSRC) Yongyou 12 and Yongyou 15, using inbred japonica super rice cultivars (IJSRC) Nanjing 44 and Ningjing 3 as control. Total nitrogen (N), phosphorus (P), and potassium (K) accumulations in IHSRC were 12.53%, 20.81%, and 17.30% higher than those in IJSRC respectively. The larger amounts of accumulated nutrients in IHSRC were mainly attributable to the high rates of nutrients accumulation before elongating and the long growth duration without premature senescence after elongating. The apparent recovery efficiency of N fertilizers, agronomic N use efficiency, and the partial factor productivity of applied N in IHSRC were all higher than those in IJSRC, whereas the physiological N use efficiency and internal N, P, and K use efficiencies of IHSRC were similar to or lower than those of IJSRC. Compared with IJSRC, the root weights of IHSRC were heavier with greater length and bigger volume, the total and active absorption areas were also larger. In conclusion, with strong and active root systems, IHSRC are more efficient in nutrient absorption than utilization.

Root Morphological Traits and Spatial Distribution under Different Nitrogen Treatments and Their Relationship with Grain Yield in Super Hybrid Rice

Succeeding in breeding super hybrid rice has been considered as a great progress in rice production in China. This on-farm study was conducted with Minirhizotron techniques to identify dynamic root morphological traits and distribution (0–30 cm) under different nitrogen treatments. Five elite super hybrid rice cultivars, Liangyoupeijiu (LYPJ), Yliangyou 1(YLY1), Yliangyou 2(YLY2), Yliangyou 900(YLY900) and Super 1000(S1000), were grown at four N levels: 0 kg ha−1 (N1), 210 kg ha−1 (N2), 300 kg ha−1 (N3) and 390 kg ha−1 (N4) in 2015 and 2016. Results showed these cultivars had greater root traits and higher grain yield under N3. Total root number (TRN) and total root length (TRL) of these cultivars reached maximum at 55 days after transplanting (DAT). The new released cultivars YLY900 and S1000 were featured with an improved root system among these cultivars. The percentage of root number on 10–20 cm soil was over 50% compared with other soil layer. A significant positive correlation was found between grain yield and both TRN and TRL at 10–20 cm soil layer (P < 0.01). Given this situation, the grain yield of super rice cultivars could be further improved by increasing the proportion of roots at 10–20 cm soil layer under suitable nitrogen management.

Polymer‐Coated Urea Application Could Produce More Grain Yield in “Super” Rice

Core Ideas Polymer‐coated urea could increase both grain yield and nitrogen use efficiency in rice production, particularly in super rice.Larger sink size, more productive tillers and deeper root distribution are important agronomic performances in super rice.Higher plant activities are important physiological traits in super rice. Extensive economic reforms have resulted in a significant decrease in the involvement of rural labor force in rice (Oryza sativa L.) production in China. One of the most effective ways in minimizing the use of labor in field management while maintaining or even increasing grain yield is by using polymer‐coated urea (PCU) instead of conventional urea (CU). This study investigated whether super rice (SR) cultivars could exhibit better yield performance and nitrogen use efficiency (NUE) under PCU application than non‐super rice (NSR) cultivars. Two representative SR cultivars and two representative NSR cultivars were field grown. Three treatments, no nitrogen application (0N), CU application, and PCU application, were conducted, the application N rate of CU and PCU were both 200 kg N ha−1. Compared to NSR cultivars, SR cultivars had larger sink size, more productive tillers, larger root biomass and deeper root distribution, higher root oxidation activity at mid‐ and late grain‐filling period, greater aboveground biomass production at mid‐ and late growth stages, and greater nonstructural carbohydrate (NSC) accumulation in the stem and more nonstructural carbohydrate per spikelet (NPS) at anthesis under PCU. Polymer‐coated urea increased grain yield and agronomic NUE by 11.6 and 5.5% in SR cultivars and 4.8 and 2.2% in NSR cultivars, respectively. We conclude that using PCU could increase both grain yield and NUE in rice production, especially in SR cultivars. Improved agronomic and physiological performance contributes to an increase in grain yield and NUE in SR cultivars under PCU.

Grain yield and water use efficiency of super rice under soil water deficit and alternate wetting and drying irrigation

This study investigated if super rice could better cope with soil water deficit and if it could have better yield performance and water use efficiency (WUE) under alternate wetting and drying (AWD) irrigation than check rice. Two super rice cultivars and two elite check rice cultivars were grown in pots with three soil moisture levels, well watered (WW), moderate water deficit (MWD) and severe water deficit (SWD). Two cultivars, each for super rice and check rice, were grown in field with three irrigation regimes, alternate wetting and moderate drying (AWMD), alternate wetting and severe drying (AWSD) and conventional irrigation (CI). Compared with that under WW, grain yield was significantly decreased under MWD and SWD treatments, with less reduction for super rice than for check rice. Super rice had higher percentage of productive tillers, deeper root distribution, higher root oxidation activity, and greater aboveground biomass production at mid and late growth stages than check rice, especially under WMD and WSD. Compared with CI, AWMD increased, whereas AWSD decreased grain yield, with more increase or less decrease for super rice than for check rice. Both MWD and SWD treatments and either AWMD or AWSD regime significantly increased WUE compared with WW treatment or CI regime, with more increase for super rice than for check rice. The results suggest that super rice has a stronger ability to cope with soil water deficit and holds greater promising to increase both grain yield and WUE by adoption of moderate AWD irrigation.

Nitrogen deficiency effects on growth and photosynthesis in no-till direct seeded super hybrid rice

Field experiments were conducted in two locations in China to determine the effects of nitrogen (N) deficiency on plant growth and leaf photosynthesis of two super hybrid rice cultivars grown under no-till direct seeded conditions. Results showed that total dry mass was reduced by 39–48% in N-deficient plants. Leaf area index was decreased by 45–58% under N-deficient conditions. Less leaf number per unit land area resulting from reduced tiller number per unit area and small leaf size were responsible for the small leaf area index in N-deficient plants. N-deficient plants had 19–26% lower leaf N content and 7–12% lower relative chlorophyll content in flag leaves. In parallel with this, net photosynthetic rate and stomatal conductance were decreased by 14–24% and 14–42%, respectively, in N-deficient plants. However, the depression of stomatal conductance did not explain the lower photosynthetic capacity because intercellular CO2 concentration was not definitely reduced in N-deficient plants. Our results highlight the need for greater fundamental understanding of the effects of N deficiency on mesophyll function in no-till direct seeded super hybrid rice.

Different characteristics of high yield formation between inbred japonica super rice and inter-sub-specific hybrid super rice

Currently, the information about different characteristics of high yield formation between inbred japonica super rice cultivars (IJSRC) and inter-sub-specific hybrid super rice cultivars (IHSRC) is quite limited. In this present study, the different characteristics of high yield formation between IJSRC (Nanjing 44 and Ningjing 3) and IHSRC (Yongyou 12 and Yongyou 15) were further investigated. Our results indicated that compared with IJSRC, IHSRC displayed a significant increase of the total spikelet numbers per square meter and had higher yields (exceeding 13.18%), which might be related to IHSRC’s more efficient use of temperature and light during the stage from elongating to heading. Moreover, with the strong ability to tiller, the leaf area indexes of IHSRC at elongating, heading and maturity stages were larger than those of IJSRC. Leaf area durations of IHSRC were also higher, in particular during the periods from elongating to heading and from heading to maturity. Although the percentages of above-ground biomass accumulation in IJSRC and IHSRC were similar, IHSRC accumulated more above-ground biomass during the periods from elongating to heading and from heading to maturity. At 30days after heading, the photosynthetic rate, chlorophyll content and the root oxidation activity of IHSRC were significantly higher. In addition, the photosynthetic functions of IHSRC flag leaves were 6–8days longer than those of IJSRC flag leaves. Although the yields of IHSRC were significantly higher than those of IJSRC, no differences in yield per day between two types of super rice were observed because of more days from sowing to maturity in IHSRC. Therefore, we concluded that both IJSRC and IHSRC had high yield per day, and the final yield depended on not only the characters of rice related to high yield formation but also the utilization of temperature and light resources in the ecological environment during their growth duration.

Effects of inorganic amendments, rice cultivars and cultivation methods on greenhouse gas emissions and rice productivity in a subtropical paddy field

With the rapidly increasing demand of rice globally, there is an urgent need to develop management strategies to improve the yields of rice crops, while at the same time minimize the possible adverse climatic impacts arising from greenhouse gas emissions from paddy fields. In this study, we investigated the influence of amendment application (steel slag and sulfate), rice cultivars (super rice cultivar, Qiuyou 6, and common rice cultivar, Hesheng 10), and cultivation methods (hand cultivation, machine cultivation, throwing cultivation) on rice yield, soil properties, as well as CH4 and N2O emissions in a subtropical paddy field in southeast China. When compared to the controls, mean CH4 emissions were significantly lower in the steel slag amendment and sulfate amendment plots by 66.1% and 23.1%, respectively, but significantly higher in the machine cultivation plots by 26.6% (P<0.05). On the other hand, we observed significantly higher mean N2O emissions from the super rice, machine cultivation, and throwing cultivation plots than those from the controls by 133.4%, 45.8%, and 172.2%, respectively (P<0.05). When taking into the account both CH4 and N2O emissions, the total global warming potential per unit yield was significantly lower in the plots amended with steel slag and sulfate than in the controls. Moreover, we found that steel slag application, machine cultivation and throwing cultivation were able to increase crop yield significantly (P<0.05). Our findings suggest that a combination of steel slag application and modernized cultivation methods, in particular throwing cultivation, would be effective in improving crop yields and mitigating greenhouse gas emissions from the subtropical paddy fields.

Exogenous application of plant growth regulators induce chilling tolerance in direct seeded super and non-super rice seedlings through modulations in morpho-physiological attributes

Recently, super rice has gained much importance due to its high yield potential while exogenous application of plant growth regulators (PGRs) is an important aspect in plant development and defense responses under stress conditions. In this study we conducted two pot experiments. Firstly, four super rice cultivars, viz. Peizataifeng, Huayou 213, Yuxiangyouzhan and Huahang 31 were subjected to a series of five chilling temperatures, i.e. 11 °C, 12 °C, 13 °C, 14 °C and 15 °C (day/night) for about 25–27 days. Secondly, seeds of Peizataifeng (super rice) and Yuejingsimiao 2 (non-super rice) were then treated with different combinations of salicylic acid (SA), brassinolide (BR), calcium chloride (CaCl2) and fulvic acid (FA) and then exposed to chilling stress at 13 °C for four days. Resultantly, Peizataifen (super rice) was found with the lowest seedling survival rate at all chilling temperatures among all four super rice cultivars, however, it was still found more resistant when compared with Yuejingsimiao 2 (non-super rice) in the second experiment. Furthermore synergistic effect of all PGRs alleviated low temperature stress in both rice cultivars by improving seedling survival rates, leaf area, seedling dry weight, seedling height, root morphology and by modulating antioxidant enzymes, improving proline content and lowering lipid peroxidation.

Yield and income effects of rice varieties with tolerance of multiple abiotic stresses: the case of green super rice (GSR) and flooding in the Philippines

AbstractWith the increasing frequency of extreme climatic events, the new challenge is to develop rice varieties that are tolerant of drought, water submergence, and salinity. There are now new high‐yielding green super rice (GSR) cultivars developed at the International Rice Research Institute with increased tolerance to multiple abiotic stresses. But a clear understanding of the economic benefits of these varieties under farmers’ production environments is not yet fully understood. In this article, we assess the yield and income effects of GSR rice varieties using a two‐year panel data from one province. We use matched samples from a propensity score matching method and a fixed‐effects model within a difference‐in‐difference (DID) framework to estimate the yield effects. The income effects were evaluated using the parameter estimates from the yield/production function model. The results of the ordinary least squares and DID fixed‐effects regressions reveal significant and positive effects of GSR varieties on yield. The most important finding is that the benefits from these varieties are strongly felt when there is flooding. This evidence was not as robust when matched samples were used. However, it is clear that the yield benefits from GSR varieties could improve rice food security and help alleviate poverty in the country.

Root Morphology Was Improved in a Late-Stage Vigor Super Rice Cultivar.

This study aimed to test the hypothesis that root morphology might be improved and consequently contributing to superior post-heading shoot growth and grain yield in late-stage vigor super rice. A pot experiment was carried out to compare yield attributes, shoot growth and physiological properties and root morphological traits between a late-stage vigor super rice cultivar (Y-liangyou 087) and an elite rice cultivar (Teyou 838). Grain yield and total shoot biomass were 7–9% higher in Y-liangyou 087 than in Teyou 838. Y-liangyou 087 had 60–64% higher post-heading shoot growth rate and biomass production than Teyou 838. Average relative chlorophyll concentration and net photosynthetic rate in flag leaves were 7–11% higher in Y-liangyou 087 than in Teyou 838 during heading to 25 days after heading. Y-liangyou 087 had 41% higher post-heading shoot N uptake but 17–25% lower root biomass and root-shoot ratio at heading and maturity than Teyou 838. Specific root length and length and surface area of fine roots were higher in Y-liangyou 087 than in Teyou 838 at heading and maturity by more than 15%. These results indicated that root-shoot relationships were well balanced during post-heading phase in the late-stage vigor super rice cultivar Y-liangyou 087 by improving root morphology including avoiding a too great root biomass and developing a large fine root system.