Panicle Differentiation Stage Research Articles

Genome-wide identification of the MADS-box gene family in Avena sativa and its role in photoperiod-insensitive oat.

Traditional spring-summer sown oat is a typical long-day crop that cannot head under short-day conditions. The creation of photoperiod-insensitive oats overcomes this limitation. MADS-box genes are a class of transcription factors involved in plant flowering signal transduction regulation. Previous transcriptome studies have shown that MADS-box genes may be related to the oat photoperiod. Putative MADS-box genes were identified in the whole genome of oat. Bioinformatics methods were used to analyze their classification, conserved motifs, gene structure, evolution, chromosome localization, collinearity and cis-elements. Ten representative genes were further screened via qRT‒PCR analysis under short days. In total, sixteen AsMADS genes were identified and grouped into nine subfamilies. The domains, conserved motifs and gene structures of all AsMADS genes were conserved. All members contained light-responsive elements. Using the photoperiod-insensitive oat MENGSIYAN4HAO (MSY4) and spring-summer sown oat HongQi2hao (HQ2) as materials, qRT‒PCR analysis was used to analyze the AsMADS gene at different panicle differentiation stages under short-day conditions. Compared with HQ2, AsMADS3, AsMADS8, AsMADS11, AsMADS13, and AsMADS16 were upregulated from the initial stage to the branch differentiation stage in MSY4, while AsMADS12 was downregulated. qRT‒PCR analysis was also performed on the whole panicle differentiation stages in MSY4 under short-day conditions, the result showed that the expression levels of AsMADS9 and AsMADS11 gradually decreased. Based on the subfamily to which these genes belong, the above results indicated that AsMADS genes, especially SVP, SQUA and Mα subfamily members, regulated panicle development in MSY4 by responding to short-days. This work provides a foundation for revealing the function of the AsMADS gene family in the oat photoperiod pathway.

Nitrogen fertilization application strategies improve yield of the rice cultivars with different yield types by regulating phytohormones

Rice (Oryza sativa L.) is the most important food crop worldwide, and its sustainable development is essential to ensure global food security. Panicle morphological and physiological characteristics plays an important role in rice yield formation. However, under different nitrogen (N) fertilization strategies, it is not clear whether the morphological and physiological state of panicles at panicle development stage affects the formation of yield. To understand how the panicle differentiation and development, and grain yield are affected by the N fertilization strategies, and clarify the relationship between related traits and yield in the process of panicle development in different cultivars. In this study consisted of no N fertilizer and four N fertilization strategies, a panicle weight type (PWT) rice cultivar, Dongfu 114 (DF114) and a panicle number type (PNT) rice cultivar, Longdao 11 (LD11) were grown in the field. The results showed that N fertilization strategies could improve the nitrogen use efficiency and yield of rice, but the response of different rice varieties to N fertilizer strategies was different. Different from the DF114, the further increase of panicle N fertilizer ratio could not further improve the yield of LD11, and the highest grain yield of DF114 and LD11 was obtained under N4 and N3 conditions, respectively. In addition, this study found that N fertilizer strategies can affect the content of phytohormones in rice at the panicle differentiation stage, and then regulate the differentiation and development of rice panicles to affect yield. It is of great significance to optimize the application mode of N fertilizer according to the characteristics of varieties to improve rice yield and ensure food security.

Number of days to reach the main plant developmental stages of irrigated rice cultivars

The objective of this study was to determine the number of days (ND) to reach the main plant developmental stages (PDS) of irrigated rice cultivars. Field experiments were carried out at the Estação Experimental Terras Baixas (ETB) of Embrapa Clima Temperado, located in the municipality of Capão do Leão, State of Rio Grande do Sul, Brazil, during 12 crop seasons, using six sowing dates in each. Ten plants from each cultivar were tagged and had each of the PDS monitored throughout the crop cycle. The results indicated that the ND to reach each of the six PDS varied according to the cycle of the cultivars and that there was statistical difference between some of them. The ND to reach the stages R1 (panicle differentiation), R4 (anthesis) and R9 (complete panicle maturity) of the cultivar IRGA 424, for example, were 63, 96 and 125, respectively. The average number of days to reach the different plant developmental stages varies according to the cycle length of the cultivars, and the subperiod of longer duration is that between the four-leaf and panicle differentiation stages (V4-R1).

Rice Cultivar Renewal Reduces Methane Emissions by Improving Root Traits and Optimizing Photosynthetic Carbon Allocation

Cultivar renewal (CR) contributes greatly to rice yield increase in China and even in the world. However, few studies were focused on the impact and mechanism of CR on field methane (CH4) emissions. A 2-year field experiment was conducted using 14 typical japonica rice cultivars released in the Yangtze River Basin of China during the last 70 years. The grain yield, root morphophysiological traits and their relationships with CH4 emissions were examined. The results showed that the grain yields of cultivars in the 1960–2010s increased by 18.8–93.9% while the CH4 emissions decreased by 9.5–41.2% compared with the 1950’s cultivars. The daily and cumulative CH4 emissions during the panicle differentiation stage (PD) were reduced significantly, which contributed greatly to the CH4 mitigation of the whole growing season. The CR notably increased root biomass, root/shoot ratio, root oxidation activity, and the total organic carbon in root exudates (ETOC), and decreased the ratios of ETOC/yield, ETOC/root biomass and ETOC/shoot biomass. Nitrogen fertilizer applied during panicle differentiation could improve the root physiology and decrease the ETOC/yield and ETOC/root, therefore reducing CH4 emissions. Our findings illustrated that CR reduced CH4 emissions by improving root traits and by optimizing the photosynthate allocation to biomass and grain yields. Applying nitrogen fertilizer during panicle differentiation could further mitigate the CH4 emissions in paddies.

Suitable varieties and high-yielding population characteristics of late season rice in the northern margin area of double-cropping rice along the Yangtze River

<p id="C2">To clarify the suitable types of rice varieties and the mechanism of high yield formation, we mainly analyzed the yield difference between<italic> indica</italic> and <italic>japonica</italic> rice in late season in the northern margin of the double-cropping rice along the Yangtze River. The experiment was conducted from 2018 to 2019 in Lujiang, Anhui province. The differences of yield and yield components, dry matter accumulation, and growth period between <italic>indica</italic> and <italic>japonica</italic> rice were compared and analyzed through 17 <italic>indica</italic> rice and 17 <italic>japonica</italic> rice varieties (strains) which were cultivated in this local area. The results showed that the overall yield level of <italic>japonical</italic> rice was similar to that of <italic>indica</italic> rice. However, compared with <italic>indica</italic> rice, the<italic> japonica</italic> rice had the characteristics of fewer yield-limiting factors, superior safety of panicle fullness, higher yield stability, and ecological safety. High-yield <italic>japonica</italic> rice mainly increased the total dry matter accumulation from transplanting to heading stage so as to improve total spikelets and yield. The effects of dry matter accumulation at different stage with different panicle types on total spikelets were quite different. Among them, the dominance period of dry matter accumulation of medium-large panicle (102.3-112.0 grains per panicle) and small panicle <italic>japonica</italic> rice (52.0-99.7 grains per panicle) are transplanting to panicle differentiation and panicle differentiation to heading stage respectively and the correlation coefficients with total spikelets were 0.709 and 0.829, respectively. Further analysis revealed that dry matter accumulation during transplanting to panicle differentiation stage of large panicle <italic>japonica</italic> rice was significantly affected by the number of tillers at tillering stage, while the dry matter accumulation during panicle differentiation to heading stage of small panicle <italic>japonica</italic> rice was affected by the number of tillers and dry weight of single stem at heading stage. In summary, this study suggested that <italic>japonica</italic> rice was a suitable late season rice variety in the northern margin area of double-cropping rice along the Yangtze River. The number of spikelets in the high-yielding <italic>japonica</italic> rice was 33.8×10³-41.0×10³ m^-2, the dry matter accumulation at maturity was 15.2-16.6 t hm^-2, and the daily yield was 58.9-64.3 kg hm^-2 d^-1. Regarding the selection of varieties, high-yield large-panicle <italic>japonica</italic> rice, such as Jia 58, Wuyujing 6571, and Changyou 5, should have strong tillering ability; while small-panicle rice varieties, such as Ningjing 7, Wuyujing 5745 and Huxiangjing 151, should have a suitable number of tillers at heading stage and dry weight of single stem. In addition, it was necessary to study the optimized cultivation techniques for high-yielding <italic>japonica</italic> rice varieties with different panicle types in order to further develop the yield potential.

Assessment of the Rice Panicle Initiation by Using NDVI-Based Vegetation Indexes

The assessment of rice panicle initiation is crucial for the management of nitrogen fertilizer application that affects yield and quality of grain. The occurrence of panicle initiation could be determined via either green ring, internode-elongation, or a 1–2 mm panicle, and was observed through manual dissection. The quadratic polynomial regression model was used to construct the model of the trend of normalized difference vegetation index-based vegetation indexes (NDVI-based VIs) between pre-tillering and panicle differentiation stages. The slope of the quadratic polynomial regression model tended to be alleviated in the period in which the panicle initiation stage should occur. The results indicated that the trend of the NDVI-based VIs was correlated with panicle initiation. NDVI-based VIs could be a useful indicator to remotely assess panicle initiation.

Effects of a One-Time Application of Controlled-Release Nitrogen Fertilizer on Yield and Nitrogen Accumulation and Utilization of Late Japonica Rice in China

A mixture of controlled-release nitrogen (N) fertilizers (CRNFs) and conventional urea (CU) as a single application of basal fertilizer could simplify fertilization in rice cultivation from the traditional and more labor-intensive fertilization strategy of multiple applications of nitrogen. However, the reported benefits of this combined approach in increasing rice yield have varied substantially for various reasons, including that various types of rice are characterized by different N requirements to obtain high yield. In this study, two late japonica rice cultivars, Jia58 (J58) and Jia67(J67), were used to determine the best combination of one of two short-acting CRNFs (release periods were 40 and 60 days) and one of three long-acting CRNFs (release periods were 80, 100 and 120 days) to apply with the CU as a one-time application of basal fertilizer. Six combinations of CRNFs were established based on their release periods: A1, 40 + 80 days; A2, 40 + 100 days; A3, 40 + 120 days; B1, 60 + 80 days; B2, 60 + 100 days; and B3, 60 + 120 days. CU applied split at basal, tillering and panicle differentiation stages, respectively as control (CK). The effects of the different treatment combinations of CRNFs on late-rice grain yield, N accumulation and N-use efficiency in a two-year field experiment were determined. Results showed that, the A2 treatment achieved the same yield as that of CK, and yield of the B2 treatment exceeded the yield of CK. Yield of J58 applied with B2 was 7.35% higher in 2018 and 7.40% higher in 2019 than that of the corresponding yield of CK; yield of J67 applied with B2 was 6.05% higher in 2018 and 6.87% higher in 2019 than that of CK. Compared with other CRNF treatments, the release of N from A2 and B2 was most synchronized with nitrogen uptake by the two cultivars, which indicates that fertilizer combination completely met the nitrogen demands during each growth stage of rice. Rice of the A2 and B2 treatments had higher N accumulation, higher aboveground biomass accumulation and LAI (leaf area index) at the heading and maturity stages and higher photosynthetic activity than those of other CRNF treatments. In conclusion, for late japonica rice in China, the application of the A2 and B2 treatments as optimal type of CRNF can achieve labor saving and yield increasing simultaneously in rice production.

Combined proteomics, metabolomics and physiological analyses of rice growth and grain yield with heavy nitrogen application before and after drought

BackgroundNitrogen application can effectively mitigate the damage to crop growth and yield caused by drought. However, the efficiency of heavy nitrogen application before drought (NBD) and heavy nitrogen application after drought (NAD) to regulate rice response to drought stress remains controversial. In this study, we profiled physiology, proteomics and metabolomics in rice variety Wufengyou 286 of two nitrogen management modes (NBD and NAD) to investigate their yield formation and the mechanism of nitrogen regulation for drought resistance.ResultsResults revealed that the yield of NBD and NAD decreased significantly when it was subjected to drought stress at the stage of young panicle differentiation, while the yield of NBD was 33.85 and 36.33% higher than that of NAD in 2017 and 2018, reaching significant levels. Under drought conditions, NBD increased chlorophyll content and net photosynthetic rate in leaves, significantly improved the activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase and catalase, and decreased malondialdehyde (MDA) content compared with NAD. NBD promoted nitrogen assimilation in leaves, which was characterized by increased activities of nitrate reductase (NR) and glutamine synthetase (GS). In addition, NBD significantly increased the contents of osmotic regulatory substances such as soluble sugar, soluble protein and free proline. Gene ontology and KEGG enrichment analysis of 234 differentially expressed proteins and 518 differential metabolites showed that different nitrogen management induced strong changes in photosynthesis pathway, energy metabolism pathway, nitrogen metabolism and oxidation-reduction pathways.ConclusionDifferent nitrogen management methods have significant differences in drought resistance of rice. These results suggest that heavy nitrogen application before drought may be an important pathway to improve the yield and stress resistance of rice, and provide a new ecological perspective on nitrogen regulation in rice.

Effects of controlled-release urea on nitrogen uptake characteristics and yield of double-cropping rice around Dongting Lake area

<p indent=0mm>The application of slow- and controlled-release fertilizer in rice production plays an important role in promoting the zero growth of fertilizer use and the sustainable development of agriculture in China. In this study, six consecutive years from 2013 to 2018 of controlled-release urea application in double-cropping rice in Hunan province were used to analyze the relationship between N uptake rate and N utilization in the above part of early- and late- rice in the main growth period by controlled-release urea application around the Dongting Lake district, and to explore the reasons for the sustained and stable yield increase of controlled-release urea on rice. The results showed that there was an obvious peak of N uptake rate in each stage of early rice by different N treatments, while N uptake in controlled-release urea (CRU) treatment was relatively delayed. And N accumulation was mainly from panicle initiation stage to heading stage, accounting for 35.31%–42.33%, followed by tillering stage to young panicle differentiation stage and heading stage to milk stage. Two obvious peaks of N uptake rates occurred in late rice from tillering stage to panicle initiation stage and from heading stage to milk stage, and the peak value was the highest at 1.0 CRU treatment. Large amount of N uptake from tillering stage to young panicle differentiation stage and heading stage to milk stage accounted for 35.92%–40.52% and 23.05%–24.58% of total amount of the whole growing period, respectively. Controlled-release urea could also significantly increase the yield of double-cropping rice, especially in early- and late- rice were treated with 0.9 CRU and 0.8 CRU respectively, and the yield increase of late rice was better than that of early rice with reduced application of controlled-release urea, and the N absorption efficiency, N agronomic efficiency and N partial productivity of early- and late- rice were significantly improved. The yield of early- and late-rice treated by CRU was significantly positively correlated with N accumulation and effective panicle number at panicle initiation stage, heading stage, milk stage and waxen stage, and the yield of late rice was significantly positively correlated with panicle length. The N accumulation of early and late rice at the panicle initiation stage was significantly negatively correlated with the agronomic and physiological rates of N fertilizer. The N partial productivity was significantly or significantly negatively correlated with the N accumulation of early rice at the panicle initiation stage, heading stage, milk stage and waxen stage, and significantly negatively correlated with the N accumulation at the heading stage of late rice. Therefore, application of controlled-release urea delayed the N uptake rate and N accumulation in the aboveground part of rice, which was beneficial to the later reproductive growth and seed setting, and could significantly improve the yield and nitrogen utilization efficiency of double-cropping rice. Combined with N absorption characteristics and grain yield of double-cropping rice, it was suggested that controlled release urea with a short release period should be used for early rice around the Dongting Lake area or applied with quick-availability N fertilizer to achieve further increase in yield level.

Effects of root morphology and physiology on the formation and regulation of large panicles in rice

Abstract At present, indica/japonica hybrid rice varieties of the Yongyou series generally show high yield and large panicles, but the physiological mechanism on the formation of large panicles is not clear. It is of great significance to understand the physiological mechanism and regulation of the formation of large panicles in super high-yield rice varieties. In this study, five groups of different rice varieties with significant differences in yield levels were selected as materials to study the contribution of large panicles to rice yield, the physiological changes in roots and canopy during the panicle differentiation stage and the regulation of large panicles by panicle nitrogen fertilizer under field and pot cultivation conditions. The results showed that 1. high-yield indica/japonica hybrid rice varieties were characterized by high spikelet number per panicle and high total number of spikelets. 2. The zeatin (Z) and zeatin riboside (ZR) contents in roots and panicles from spikelet primordium differentiation (SPD) to pistil and stamen formation (PSF), root activity (root dry weight, root oxidation activity, root bleeding rate, root total absorbing surface area and root active absorbing surface area) and non-structural carbohydrate (NSC) accumulation in stems from pollen mother cell meiosis (PMC) to pollen filling (PF) were very significantly and positively correlated with spikelet number per panicle. 3. Compared with 0 N (no panicle nitrogen fertilizer), the number of spikelets per panicle and total spikelets of Yangdao 6 and Yongyou 1540, the Z + ZR contents in panicles and roots during SPD-PSF, and the root activity and NSC accumulation in stems during PMC-PF were significantly improved under LN (panicle nitrogen fertilizer at a rate of 1.2 g pot-1) and MN (panicle nitrogen fertilizer at a rate of 2.4 g pot-1). High Z + ZR contents in young panicles and roots during SPD-PSF and large amounts of root activity (root dry weight, root oxidation activity, root bleeding rate, root total absorbing surface area and root active absorbing surface area) and NSC accumulation in stems during PMC-PF were important physiological factors in the formation of large panicles in super high-yield indica/japonica hybrid rice. Improvements in the above indexes during the panicle differentiation stage are likely contribute to the formation of large panicles and the increase in rice yield.

Optimization of nitrogen fertilizer management for improving rice grain yield and nutrient accumulation and mobilization in saline‐alkaline soils

AbstractSoil salinity and alkalinity are key abiotic stresses that limit crop growth and yield worldwide. Balanced N fertilization is important for improving rice (Oryza sativa L.) yield via efficient utilization of P and K under saline and alkaline soil conditions. In this study, a japonica rice cultivar, Kenjing 8, was used to investigate the effects of N fertilizer on rice yield, as well as N, P, and K status, in a 2‐yr field experiment in saline‐alkaline soil in Heilongjiang Province, northeast China. The plants were assigned to the following five treatment groups: no N fertilizer, or conventional, balanced, reduced, and postponed N fertilizer management. Compared with conventional N management practice, balanced and reduced N management practices increased the concentrations of N, P, and K in the leaves, stem‐sheaths, and panicles at full heading (FH) and maturity; however, postponed N management led to the opposite results. Balanced N management increased N, P, and K mobilization to the leaves (from FH to maturity) by 49, 43, and 67%, respectively, resulting in the highest crop yields among all the N management practices studied. Furthermore, rice yield was positively correlated with N, P, and K accumulation and rates of nutrient mobilization to the leaves, stem‐sheaths, and panicles at maturity. The application of 150 or 135 kg N ha−1, and the proportion of 4:3:1:2 in the pre‐transplanting, mid‐tillering, panicle initiation, and panicle differentiation stages, may increase rice yield and facilitate efficient utilization of nutrients in saline‐alkaline soil.

ITRAQ-based quantitative proteomic and physiological analysis of the response to N deficiency and the compensation effect in rice

BackgroundThe crop growth compensation effect is a naturally biological phenomenon, and nitrogen (N) is essential for crop growth and development, especially for yield formation. Little is known about the molecular mechanism of N deficiency and N compensation in rice. Thus, the N-sensitive stage of rice was selected to study N deficiency at the tillering stage and N compensation at the young panicle differentiation stage. In this study, a proteome analysis was performed to analyze leaf differentially expressed proteins (DEPs), and to investigate the leaf physiological characteristics and yield under N deficiency and after N compensation.ResultsThe yield per plant presented an equivalent compensatory effect. The net photosynthetic rate, optimal/maximal quantum yield of photosystem II (Fv/Fm), soil and plant analyzer development (SPAD) value, and glutamic pyruvic transaminase (GPT) activity of T1 (N deficiency at the tillering stage, and N compensation at the young panicle differentiation stage) were lower than those of CK (N at different stages of growth by constant distribution) under N deficiency. However, after N compensation, the net photosynthetic rate, Fv/Fm, SPAD value and GPT activity were increased. Using an iTRAQ-based quantitative approach, a total of 1665 credible proteins were identified in the three 4-plex iTRAQ experiments. Bioinformatics analysis indicated that DEPs were enriched in photosynthesis, photosynthesis-antenna proteins, carbon metabolism and carbon fixation in the photosynthetic organism pathways. Moreover, the photosynthesis-responsive proteins of chlorophyll a-b binding protein, ribulose bisphosphate carboxylase small chain and phosphoglycerate kinase were significantly downregulated under N deficiency. After N compensation, chlorophyll a-b binding protein, NADH dehydrogenase subunit 5, NADH dehydrogenase subunit 7, and peroxidase proteins were significantly upregulated in rice leaves.ConclusionThrough physiological and quantitative proteomic analysis, we concluded that a variety of metabolic pathway changes was induced by N deficiency and N compensation. GO and KEGG enrichment analysis revealed that DEPs were significantly associated with photosynthesis pathway-, energy metabolism pathway- and stress resistance-related proteins. The DEPs play an important role in the regulation of N deficiency and the compensation effect in rice.

Dissection of mechanisms for high yield in two elite rice cultivars

Understanding mechanisms underlying high yield in elite cultivars and identifying new options to further increase rice yield are major focuses of current rice research. In this work, we develop a general method to tackle the above two challenges using two outstanding indica cultivars, i.e., Huang-Hua-Zhan (HHZ) and Yang-dao 6 (9311), which differ in their strategies to gain high yields. Briefly, HHZ grew slower during seedling stage, whereas accumulated more biomass from tillering to heading stage, and had a shorter leaf photosynthetic functional duration after heading; in contrast, 9311 had stronger seedling vigor, but less biomass accumulation from tillering to heading stage, and longer leaf photosynthetic functional duration after heading. To identify the mechanisms underlying these two different strategies, we dissected factors controlling daily canopy photosynthesis at four different growth stages throughout the growing season using a computational approach. Results showed that higher leaf area index (LAI) due to larger leaf width, regardless of a relatively lower leaf light-saturated photosynthetic rate, contributed to higher canopy photosynthesis and hence stronger seedling vigor of 9311 when LAI was low, whereas these same features decreased canopy photosynthetic rate at young panicle differentiation stage when LAI was high; while instead of increasing canopy photosynthesis to support seedling growth, lower LAI due to smaller leaf width, together with higher leaf light-saturated photosynthetic rate, favored biomass accumulation of HHZ between the late tillering stage and the heading stage. Concurrently, computational simulations revealed that earlier drooping of the panicle of HHZ could increase upper leaves’ light intercept and thus canopy photosynthesis at heading stage by reducing shading from panicles, whereas higher leaf nitrogen content was the most important factor for higher canopy photosynthesis of 9311 during grain filling. Overall, the method presented here can be used to quantitatively identify key factors that limit canopy photosynthetic efficiency of current elite cultivars, which is the basis for crop yield potential, and can be used as targets for rice yield improvement by traditional breeding approaches or by genomic editing technologies.

Analysis of main metabolisms during nitrogen deficiency and compensation in rice

Compensatory effect is observed during the process of gradual adaptation of plants to abnormal environmental conditions; nitrogen fertilizer compensation has been extensively studied in rice production in recent years. However, metabolite production of the phenomenon has not been studied clearly. In this study, we used super hybrid early rice as the material and planted it in a barrel. Experiments were performed under two conditions of treatment, namely, CK (normal quantities of nitrogen fertilizer distribution at different growth stages) and T1 (nitrogen deficiency at tillering stage and compensatory application at young panicle differentiation stage). Liquid chromatography–mass spectrometry (LC–MS) was used to analyze metabolomics of rice leaves under conditions of nitrogen deficiency and compensation after the same period of CK treatment. Results showed that there was a significant difference between T1 and CK metabolites. The levels of stress-resistant substances and amino acid substitution product nitrogen deficiency increased under T1 treatment compared to CK, and the metabolites were consumed as the energy source. However, after compensation, the levels of the stress response products returned to normal, lipids were synthesized in large quantities, and fatty acid accumulation had increased.

Environmental Compensation Effect and Synergistic Mechanism of Optimized Nitrogen Management Increasing Nitrogen Use Efficiency in Indica Hybrid Rice

Modern rice cultivation relies heavily upon inorganic nitrogen fertilization. Effective fertilizer management is key to sustainable agricultural development. Field and pot trials were conducted in 2014–2016, including a 15N-labeled urea pot experiment (2014) to investigate mechanism by which optimized nitrogen fertilizer application (OFA) increases nitrogen utilization efficiency (NUE). Results showed that the applied nitrogen recovery efficiencies with OFA were 71.71%, 110.17%, and 51.38% higher than those obtained with traditional nitrogen fertilizer application (TFA) in 2014, 2015, and 2016, respectively. These improvements are attributed mainly to the high recovery efficiency rates derived from spikelet-developing and spikelet-promoting fertilizer applications at the jointing stage and 15–20 d after jointing. Under OFA, the amount of nitrogen fertilizer applied at the early stages was half that used in TFA, which not only promoted the absorption of soil nitrogen, but also reduced nitrogen loss to the environment, as the NUE of basal and tillering fertilizer was only about 22%. Nitrogen applied during the panicle differentiation stage increased the expression of ATM1;1, a NH4+ transporter in roots. This effect significantly improved the uptake of nitrogen derived from fertilizer from jointing to heading stage. Up-regulation of the expression and activity of GS and GOGAT at the panicle differentiation and grain-filling stages promoted nitrogen translocation from vegetative organs to reproductive organs. The uptake of nitrogen derived from fertilizer increased from 22.51% in TFA to 35.58% in OFA. Nevertheless, rice absorbs most of the nitrogen it requires from the soil. The OFA treatment could effectively utilize the environmental compensation effect, promote the absorption and transport of nitrogen, and ultimately lead to improvement in NUE. Future research should aim to understand the soil nitrogen supply capacity in order to apply nitrogenous fertilizer in such a way that it sustains the nitrogen balance.

Comprehensive metabolomic, proteomic and physiological analyses of grain yield reduction in rice under abrupt drought-flood alternation stress.

Abrupt drought-flood alternation (T1) is a meteorological disaster that frequently occurs during summer in southern China and the Yangtze river basin, often causing a significant loss of rice production. In this study, the response mechanism of yield decline under abrupt drought-flood alternation stress at the panicle differentiation stage was analyzed by looking at the metabolome, proteome as well as yield and physiological and biochemical indexes. The results showed that drought and flood stress caused a decrease in the yield of rice at the panicle differentiation stage, and abrupt drought-flood alternation stress created a synergistic effect for the reduction of yield. The main reason for the decrease of yield per plant under abrupt drought-flood alternation was the decrease of seed setting rate. Compared with CK0 (no drought and no flood), the net photosynthetic rate and soluble sugar content of T1 decreased significantly and its hydrogen peroxidase, superoxide dismutase, peroxidase activity increased significantly. The identified differential metabolites and differentially expressed proteins indicated that photosynthesis metabolism, energy metabolism pathway and reactive oxygen species response have changed strongly under abrupt drought-flood alteration stress, which are factors that leads to the rice grain yield reduction.

Comprehensive metabolomic and proteomic analysis in biochemical metabolic pathways of rice spikes under drought and submergence stress

Drought and submergence are the main adverse factors affecting plant growth and yield formation in parts of China, especially in the Yangtze River region. In this study, T1 (drought duration: 10 d), T2 (submergence duration: 8 d) and CK (control) treatments were applied. This work aimed to study the changes in metabolic pathways of rice under drought and submergence stress during the panicle differentiation stage. The identification and analysis of differential metabolites and differentially expressed proteins functions indicate that drought and submergence mainly promoted the energy metabolism pathway, carbon fixation in photosynthetic organism pathway, carbohydrate metabolic process, and reactive oxygen species (ROS) metabolic process functions. Under drought stress, the inhibition of photosynthetic rate is mainly through stomatal conductance restriction, and flavonoid pathway regulates the metabolic process of ROS. Under submergence stress, the electron transfer chain was destroyed to inhibit the photosynthetic rate, and the antioxidant system was activated to regulate the metabolism of ROS. The changes in related enzymes or proteins in metabolic regulatory networks are analyzed, which will be conducive to understanding the response mechanism of rice drought and submergence more deeply and provide a scientific basis for rice drought and submergence prevention and mitigation, and the breeding of drought- and submergence-resistant varieties.

Response to Nitrogen Deficiency and Compensation on Physiological Characteristics, Yield Formation, and Nitrogen Utilization of Rice.

Based on the theory of ecological crop nutrient deficiency and compensation effect, the nitrogen (N) deficiency at tillering stage and N compensation at young panicle differentiation stage in rice (Oryza sativa L.) was selected to study. Four N treatments were treated, and the effects of N deficiency and compensation were investigated on grain yield, N uptake and utilization and the physiological characteristics of rice. The results showed that the yield per plant presented an equivalent compensatory effect. Double N compensation led to superiority in the number of effective panicle per plant, increased the activity of nitrate reductase and glutamine synthetase. The content of endogenous growth-inhibitory hormone abscisic acid (ABA) decreased in the leaves, photosynthesis was enhanced, and the number of tillers per plant increased after double N compensation. During maturation stage, the panicle dry weigh in T1 (double N compensation at young panicle differentiation stage, after N deficiency at tillering stage) was higher than that in CK1 (constant supply of N throughout different stages of growth) and the biomass per plant in T1 increased by 1.47% compared with CK1. N contents in all organs, N accumulation, and total N content were all higher in T1 during maturation stage. Moreover, N agronomic efficiency, N physiological efficiency, and N partial factor productivity were optimized for T1 and CK2 (constant N compensation at young panicle differentiation stage, after N deficiency at tillering stage) compared with CK1. This study contributes to the understanding of the physiological mechanisms underlying the compensation of N deficiency in rice.

The research progress and prospects of two-line hybrid rice in China

Two-line hybrid rice is new technology for exploiting rice heterosis established based on the discoveries of photo- thermo-sensitive genic male sterile (PTGMS) rice in China. The male fertility alteration of PTGMS line was controlled by recessive nuclear genes in sporophyte and induced by day-length and temperature during young panicle differentiation stage. Compared with three-line hybrid rice technology, it has three advantages: (1) The sterility is controlled by recessive nuclear genes. Any genotype with good combining ability can be used as a male parent. The frequency of obtaining heterotic hybrids in testcrosses is higher than in three-line system. (2) It simplifies the process of hybrid breeding program and shortens the breeding period for rapidly developing new hybrid rice. (3) It provides more kinds of sterile lines for diversifying hybrid rice. More than 300 PTGMS lines and over 900 two-line hybrid rice hybrids were developed and certificated in past three decades, and released in twenty provinces of China. The area covered under two-line hybrid rice was 5.5 million hectares yearly on the average, occupying 35% of total area of hybrid rice planting. Developing PTGMS lines with resistances to multiple-diseases and insect pests, short growth duration and lodging tolerance, exploiting indica-japonica heterosis for increasing yield, and ensuring safe and stable two-line hybrid rice seed production, will be the tasks for further maintaining and expanding two-line hybrid rice in future.

English

The objective of this study was to evaluate the agronomic traits of BRS 610 forage sorghum, based on developmental stages and defoliation levels. The experiment was conducted in a protected environment, located in Uniao experimental farm, in Nova Xavantina-MT, in vases with 8 dm-3 capacity in soil classified as dystrophic red latosol. The experimental design was a randomized block, arranged in a 4 x 3 + 1 factorial, four stages of defoliation [three expanded leaves (15 days after emergence of plants - DAE), six expanded leaves (30 DAE), panicle differentiation (45 DAE), booting (60 DAE)] and three levels of defoliation [(33, 66 and 99%) and an additional treatment without defoliation], making the total of 13 treatments with three replications. BRS 610 sorghum crop was used. It was evaluated plant height, stem diameter, root dry mass and shoot dry mass. Except for plant height and stem diameter, for the other variables there were significant influences of defoliation levels. To root mass and shoot dry mass it was verified that less intense defoliation and the early stages affect less those variables. To root dry mass, reductions are evident up to 66.36% when the plants are submitted to total leaves removal at the stage of panicle differentiation. The production of shoot dry mass of the BRS 610 sorghum is affected when submitted to any level and defoliation stage. Key words: Forage, silage, Sorghum bicolor (L.) Moench.