Precision drill sowing in seedling trays offers an innovative seedling-raising approach to reducing sowing rates per tray and thereby decreasing seed input and production costs in machine-transplanted high-quality hybrid rice production. However, farmers may be concerned that reduced seed input could decrease grain yield by limiting panicle number. We hypothesized that combining precision drill sowing in seedling trays with an appropriately reduced hill spacing could alleviate this concern. To test this hypothesis, two-year field experiments were conducted using two high-quality hybrid rice varieties. Grain yield and associated agronomic traits were compared between a conventional machine-transplanted system involving broadcast sowing in seedling trays followed by transplanting at the standard hill spacing (T1) and an alternative system involving precision drill sowing in seedling trays followed by machine transplanting at a reduced hill spacing (T2). Compared with T1, T2 had 38%, 24%, and 17% lower sowing rate per tray, hill spacing, and seed input, respectively. Averaged across two varieties and two years, T2 achieved a 7% higher grain yield and a 29% higher yield-to-seed ratio than T1. Compared with T1, T2 increased the productive tiller rate and panicles per m2 by 12%, specific leaf weight at heading by 7%, radiation use efficiency by 9%, and aboveground biomass at maturity by 11%. These results confirm our hypothesis, indicating that T2 improves yield performance in machine-transplanted high-quality hybrid rice by increasing productive tiller rate and panicle number per m2, as well as enhancing specific leaf weight, radiation use efficiency, and biomass production.

Rice production is increasingly challenged by flooding stress because of global warming and rising sea levels. As the world’s most important staple crop, rice is highly vulnerable to anaerobic and submergence conditions that occur during flooding, particularly at the germination and vegetative stages. Anaerobic environments hinder seedling establishment during germination, while prolonged submergence during the vegetative stage impairs growth, ultimately reducing yield and grain quality. These stresses, driven by extended inundation, trigger a cascade of detrimental physiological responses and represent a major barrier to stable rice production and global food security. In this review, we examine the effects of flooding on rice growth at both the germination and vegetative stages. We further summarize recent advances in the identification of flooding-tolerant germplasm, QTL mapping, genome-wide association study, transcriptomic and proteomic analyses, and other molecular studies. Subsequently, we highlight potential cultivation and regulatory strategies, including genetic, morphological, physiological, and endogenous hormone-related approaches, aimed at enhancing tolerance to anaerobic and submergence stress. Together, these approaches underscore the promise of integrating molecular insights with agronomic practices to mitigate flooding damage and support sustainable rice production.

High temperature significantly impacts grain appearance quality, yet few studies have focused on identifying new quantitative trait loci (QTLs)/genes related to these traits under heat stress during the flowering stage in rice. In this study, a natural population of 525 rice accessions was used to identify QTLs and candidate genes associated with grain appearance quality using a Genome-Wide Association Study under heat stress. We identified 25 QTLs associated with grain length (GL), grain width (GW), and grain chalkiness (GC) under heat stress across 10 chromosomes in the three rice populations (full, indica, and japonica). Notably, three sets of overlapping QTLs were identified (set 1: qHTT-L3 and qHTT-XL3; set 2: qHTT-C5 and qHTT-XC5; set 3: qHTT-L11.1 and qHTT-GL11), located on chromosomes 3, 5, and 11, respectively. Haplotype analysis indicated that Hap1 is the superior haplotype, and pyramiding more than two superior alleles improved rice grain appearance quality (longer GL, wider GW, and lower GC) in high-temperature environments. Based on RNA-seq, qRT-PCR and functional annotations analysis, LOC_Os05g06920, LOC_Os05g06970, and LOC_Os11g28104 were highly expressed, identifying them as the high-priority candidate genes for QTLs linked to grain appearance quality (GL, GW, and GC) under heat stress. Expression analysis revealed that LOC_Os05g06920, which encodes a relA-SpoT-like protein RSH4, and LOC_Os11g28104, which encodes a protein kinase with a DUF26 domain, were highly expressed in seeds, leaves, and shoots. And LOC_Os05g06970, encoding a peroxidase precursor, exhibited high expression levels in roots. Compared to the wild-type (WT) plants, the mutants of LOC_Os05g06920, LOC_Os05g06970, and LOC_Os11g28104 exhibited increased GL and grain length-to-width ratio, but reduced GW under both natural and heat stress conditions, while the LOC_Os05g06970 and LOC_Os11g28104 mutants significantly increased the chalky grain rate and grain chalkiness degree under natural conditions. Furthermore, the LOC_Os05g06920, LOC_Os05g06970, and LOC_Os11g28104 mutants showed a lower decline in grain appearance quality traits than the WT after high-temperature treatment. These findings suggest that LOC_Os05g06920, LOC_Os05g06970, and LOC_Os11g28104 play crucial roles in regulating both grain development and heat tolerance under heat stress at anthesis, thus affecting grain appearance quality in rice. Our results provide a promising genetic resource for improving rice grain appearance quality under heat stress.

China aims to increase rice production and reduce associated negative environmental impact. However, increasingly limiting and expensive rural labor has driven a shift from double- to single-season rice, posing a threat to national food security. Here, we evaluated the impact of an alternative ratoon rice system on production and environmental outcomes using smallholders’ survey data together with spatial crop modeling. We showed that ratoon rice adoption would ensure rice self-sufficiency and drastically reduce nutrient losses, pesticide use, greenhouse gas emissions, and labor requirements. We conclude that ratoon rice is a viable option to meet the dual goal of increasing production and reducing negative environmental impacts.

Rice (Oryza sativa L.) cultivation using direct seeding is susceptible to chilling stress, particularly during seed germination and early seedling growth in the early season of a double cropping system. Alternatively, seed priming with various plant growth-promoting hormones is an effective technique to promote rapid and uniform emergence under chilling stress. Therefore, we evaluated the impact of gibberellin A3 (GA3) and brassinolide (BR) priming on rice seed emergence, examining their proteomic responses under low-temperature conditions. Results indicated that GA3 and BR increased the seed germination rate by 22.67% and 7.33% at 72 h and 35% and 15% at 96 h compared to the control (CK), respectively. Furthermore, proteomic analysis identified 2551, 2614, and 2592 differentially expressed proteins (DEPs) in GA, BR, and CK, respectively. Among them, GA exhibited 84 upregulated and 260 downregulated DEPs, while BR showed 112 upregulated and 102 downregulated DEPs, and CK had 123 upregulated and 81 downregulated DEPs. Notably, under chilling stress, both GA3 and BR are involved in peroxide metabolism, phenylpropanoid biosynthesis, and inositol phosphate metabolism, enhancing antioxidant capacity and providing energy substances for germination. In addition, GA3 triggers the specific regulation of stress responsive protein activation, GTP activation, and ascorbic acid biosynthesis and promotes the stability and integrity of cell membranes, as well as the synthesis of cell walls, providing physical defense for seeds to resist low temperatures. At the same time, BR triggers specific involvement in ribosome synthesis and amino acid synthesis, promoting biosynthetic ability and metabolic regulation to maintain plant life activities under low-temperature stress. Furthermore, the various genes’ expression (OsJ_16716, OsPAL1, RINO1) confirmed GA3 and BR involved in peroxide metabolism, phenylpropanoid biosynthesis, and inositol phosphate metabolism, enhancing antioxidant capacity and providing energy substances for germination. This study provides valuable insights into how rice seed embryo responds to and tolerates chilling stress with GA3 seed priming.

Introduction/BackgroundGlobal warming greatly limits the productivity of rice. Rice plants are highly sensitive to heat stress at the flowering stage. The selection of heat-tolerant varieties is considered the most effective approach for ensuring global food security in the coming decades.MethodsBased on previous screening and QTL localization results, we selected tolerant varieties (Huang Huazhan, HZ) and susceptible varieties (Yang Dao6, YD) of rice and studied their physiological characteristics, gene expression responses, and proteomic differences of their anthers under heat stress. The differentially expressed proteins (DEPs) were validated by real-time PCR.ResultsThe activities of the antioxidant enzymes CAT, SOD, POD, and APX were 8.36%, 9.56%, 20.61%, and 25.34% higher in HZ than in YD under heat stress, respectively. Similarly, the content of proline and soluble sugar was 8.32% and 14.47% higher in HZ than in YD, respectively. The content of MDA and H2O2 was 8.11% and 39.5% lower in HZ than in YD, respectively. The ratio of endogenous GA3/ABA in HZ was 10.65, which was significantly higher than that of YD (3.84). In addition, we validated the candidate genes LOC_Os08g07010 and LOC_Os08g07440 that our team located in 2021, and the result showed that the expression of these two heat-tolerant genes in the anthers was significantly higher in HH than in YH. DEPs involved in the response to heat stress were identified by TMT proteomics, five upregulated and three downregulated differential expression proteins in HH. DEPs were verified by RT-qPCR.DiscussionThese results provide new insights into the physiological characteristics, dominant DEPs, and gene expression responses in both rice varieties under heat stress. Our results indicate that the antioxidant and osmoregulatory capacities, the ratio of endogenous GA3 and ABA, these DEPs are mainly involved in the pathways of phenylpropanoid biosynthesis, ubiquitin-mediated proteolysis, carbohydrate metabolism, thiamine metabolism, protein processing in the endoplasmic reticulum, and folding, sorting, and degradation were upregulated to a greater degree in HZ than in YD. Additional studies were performed to clarify the roles of these proteins in response to heat stress.

【Objective】The objective of this study was to investigate the effects of direct seeding cultivation on the growth period, lodging resistance, yield and economic benefits of different rice varieties, in order to provide a theoretical basis for the application and promotion of mechanized direct seeding rice.【Method】For the early rice in 2020 and 2021, the conventional rice varieties with a large area in Guangxi production, including Guiyu 9, Guiyu 11, Guiyefeng, Guangliangxiang 2, and hybrid rice Y Liangyou 1, were used as test materials. In the field, using the traditional manual transplanting as a control, the field was accurately direct seeding. A split plot design was used in this experiment with planting method as the main plot, with rice varieties as the split plot, and set up three replications. The length of the growth period was observed, the morphology of main stem and the characteristics of the basal stem, as well as the lodging indicators such as breaking resistance, bending moment and lodging index, were calculated, the yield and yield components were measured at the maturity stage, and the cost and economic benefits were calculated too.【Result】(1) The growth period of direct seeding was shortened by about 2-6 days, which was mainly reflected in the period from sowing to the beginning of young spike. (2) The lodging resistance of direct seeding rice was relatively poor, and its plant height, center of gravity height and panicle dry weight were lower than that of transplanted rice; The stem thickness, wall thickness, fresh weight and dry weight of its N2 stem were also lower than that of transplanted rice, and the length of the stem of direct seeding rice was higher than that of transplanted rice, which might be the main reason for the weak lodging resistance of the direct rice. (3) Among the varieties tested, the actual yields of the remaining four rice varieties were lower than those of transplanted under direct-seeded cultivation, except for Yliangyou1. For varieties with relatively short growth period in the test materials, the yield under direct seeding conditions is significantly lower than that of transplanting, while for varieties with relatively long growth period, the yield difference between planting methods is not significant, among the yield components, the increase in the number of grains per panicle and the seed setting rate were the main factors for increasing the yield of direct seeding rice. (4) From the analysis of economic benefits, among the varieties tested, Guiyu 11, which had a shorter growth period, had a significantly lower yield and economic benefit in direct seeding method, and the economic benefits of direct seeding rice of the remaining four varieties were higher than those of transplanted rice; The main reason for this was that direct seeding rice saved labor costs in seedling and transplanting link.【Conclusion】At present, it was an urgent to develop a light and simple production model of rice with the main goal of preserving area and increasing efficiency. Compared with transplanted rice, direct seeding rice had obvious advantages, such as shortening the growth period and reducing production costs. There was a certain risk of lodging, for the yield was easily affected by variety characteristics and environmental factors. Therefore, the lodging-resistant varieties with medium maturity, reasonable stem length at the base, thick stems and thick stem walls could be selected in the direct seeding cultivation of early rice. In cultivation management, the proportion of ear fertilizer should be appropriately increased to compensate for insufficient number of grains per panicle and seed setting rate could improve the yield of direct seeding rice.

Introduction/Background Direct-seeded rice is exceptionally vulnerable to chilling stress, especially at the seed germination and seedling growth stages in the early season of the double cropping system. Methods Therefore, we conducted two experiments to evaluate the role of various seed primings and their different concentrations of plant growth regulators [experiment 1—abscisic acid (ABA), gibberellin (GA 3 ), salicylic acid (SA), brassinolide (BR), paclobutrazol, uniconazole (UN), melatonin (MT), and jasmonic acid (JA)] and osmopriming substances (chitosan, polyethylene glycol 6000 (PEG6000), and CaCl 2 ) and experiment 2—GA, BR (two best), CaCl 2 (worst), and control (CK)] on rice seedlings under low temperature condition. Results Results showed that the maximum germination rate of 98% was recorded in GA 3 (10 mgL −1 ) and BR (0.3 mgL −1 ) among treatments. Compared to CK, root and shoot length were improved in ABA (0.5 mgL −1 ) and GA 3 (100 mgL −1 ) by 64% and 68%, respectively. At the same time, root and shoot weights (fresh and dry) were enhanced in Paclobutrazol (300 mgL −1 ) and GA3 among treatments. Furthermore, the average root volume, average root diameter, and total root surface area were increased by 27%, 38%, and 33% in Paclobutrazol (300 mgL −1 ), Paclobutrazol (200 mgL −1 ) and JA (1 mgL −1 ) treatments, respectively compared to CK. In the second experiment, a respective increase of 26%, 19%, 38%, and 59% was noted in SOD, POD, CAT, and APX enzyme activities in GA treatment compared to CK. Similarly, proline, soluble sugar, soluble protein, and GA content were also improved by 42%, 25.74%, 27%, and 19%, respectively, in GA treatment compared to CK. However, a respective reduction of 21% and 18% was noted in MDA and ABA content in GA treatment compared to CK. Our finding highlighted that better germination of primed-rice seedlings was associated with fresh and dry weights of the roots and shoots and the average root volume of the seedlings. Discussion Our results suggested that GA 3 (10 mg L −1 ) and BR (0.3 mg L −1 ) seed priming prevent rice seedlings from chilling-induced oxidative stress by regulating antioxidant enzyme activities and maintaining ABA, GA, MDA, soluble sugar, and protein content. However, further studies (transcriptome and proteome) are needed to explore the molecular mechanisms involved in seed priming-induced chilling tolerance under field conditions.

The "super rice" breeding program in China has been successful in developing high-yielding hybrids, including few with high harvest index values. However, there is limited information on the relationship between lodging resistance and harvest index, and the mechanisms underlying the relationship in super-rice hybrids. In this study, a two-year field experiment was conducted to compare lodging resistance and its related traits between two super rice hybrids differing in harvest index, i.e., Guiliangyou 2 (G2) with a high harvest index and Y-liangyou 1 (Y1) with a typical harvest index of modern high-yielding rice varieties. Results showed that compared to Y1, G2 was lower in plant height due to its lower aboveground N uptake, and its higher stem breaking resistance (i.e., lower stem breaking index) resulted from a lower stem height at its center of gravity. Consequently, G2 had a higher lodging resistance (i.e., lower plant lodging index) than Y1. This study suggests that developing super-rice hybrids with high harvest index values is a possible way to achieve both high grain yield and strong lodging resistance in rice.

Photosynthesis is responsible for 90–95% of organic matter in crop yield. The light energy utilization rate of high-yielding rice varieties is 1.0–1.5%, but the ideal value is about 3–5%. Yield can be further improved by improving photosynthetic function. Through the initial screening and re-screening of 220 Southeast Asian germplasm resources, we found that the net photosynthetic rate of Southeast Asian germplasm resource C1 was 36.96 μmol m−2 S−1, which is close to that of C4 plant maize and 3.26 times higher than that of Southeast Asian germplasm resource G164 at 11.26 μmol m−2 S−1. Using C1 and G164 as materials, we compared the tissue structure, chloroplast ultrastructure, photosynthetic physiological indicators, and proteomics of sword leaves to determine the factors affecting photosynthetic function. Compared with G164, C1 exhibited increased number of vascular bundles, increased stomatal size and density, more abundant and neatly arranged chloroplasts and thylakoid grana, and higher chlorophyll fluorescence parameters. The activities and contents of the key photosynthetic enzyme Rubisco were higher in C1 than in G164. The two germplasm resources were subjected to iTRAQ analysis, and the results showed that compared with C1, nine proteins were down-regulated and one protein was up-regulated and associated with photosynthetic electron transport in G164; a total of 17 differential proteins were associated with CO2 fixation, and nine were up-regulated and eight differential proteins were down-regulated in G164. The identified genes encode proteins in the photosynthesis and carbon fixation pathways, and the changes in gene expression were verified by real-time qPCR. The gene expression patterns were consistent with the protein expression patterns. The results suggest that most differential proteins are involved in electron transfer from PSII to PSI and in the CO2 fixation pathway, and increasing the levels of such proteins can effectively enhance the photosynthetic efficiency. C1 can be used as a donor material for selection of high light efficiency varieties and in-depth photosynthesis studies.

[Objective] Under the double stress of low temperature and waterlogging stress, some rice varieties area were evaluated, evaluation of the ability of early rice varieties to withstand low temperature and waterlogging stress during bud stage and seedling stage in double cropping rice area of Guangxi was conducted, and screened out the rice varieties suitable for early rice direct seeding, so as to provide reference for suitable early rice varieties of direct seeding in Guangxi. [Method] Based on the artificial simulated low temperature environment, the germination seeds of 25 tested rice varieties were treated with low temperature and waterlogging [daily average temperature 5 °C (12 h light +12 h darkness), water depth of germination box was 5 cm] and control [daily average temperature 5 °C (12 h light+12 h darkness), water depth of germination box was 3 mm]. The seeds of tested varieties after accelerating germination were cultured for 10 d. After this treatment, the seeds were restored to 28 T and continued to grow for 10 d. The seedling rate, root length, root numbers, seedling height, fresh weight per plant, above-ground fresh weight and root fresh weight were measured, and their low temperature and waterlogging tolerance abilities were comprehensively evaluated by membership function analysis and correlation analysis. [Result] Seedling rate stress coefficient of 25 rice varieties was different, the variation was 0-1.00, the average stress coefficient was 0.935. Through the correlation analysis of stress coefficient, there was significant positive correlation between seedling rate and above-ground fresh weight per plant under stress ( P<0.05, the same below), and positive correlation with other traits, but the correlation did not reach significant level ( P>0.05, the same below). Seedling height was extremely positively correlated with root length, above-ground fresh weight and root fresh weight ( P< 0.01, the same below), and significantly positively correlated with root number and plant fresh weight. According to the average results of membership function, the tested varieties were divided into three types: strong, medium and weak tolerance. There were nine varieties with strong tolerance, they were: Guiyu 12, Wushansimiao, High quality farm seed 2, Guiyu 9, Jinsimiao, Xiangzhou fragrant rice, Hexifengzhan, Y liangyou 1, Guiyu 11. Compared with the medium tolerancetypes and weak tolerance types, the rice varieties with strong tolerance hadimprovement in root length, root number, root fresh weight and seedling height. Compared with the control, under the condition of low temperature and waterlogging stress (LT+W), all measurements of plant traits were decreased, and the root length decreased the most, reaching 19.0%, followed by root fresh weight and root number, which decreased by 18.2% and 16.3% respectively. [Conclusion] The key indexes of tolerance to low temperature and waterlogging stress of direct seeding early rice are seedling rate, root indexes (root length, root number and root fresh weight) and seedling height. Nine varieties such as Guiyu 12 can be directly used in the production of direct seeding rice in Guangxi, and can also provide materials for the study of the mechanism of rice tolerance to low temperature and waterlogging and the cultivation of suitable direct seeding rice varieties. 摘要: 【目的】 对广西双季稻区早稻品种芽期和幼苗期耐低温淹水能力进行评价, 为广西稻区直播早稻品种选择 供参考。 【方法】 以25个水稻品种为试验材料, 基于人工模拟低温环境, 设低温淹水[日均温5 °C:(12 h光照+ 12 h黑 暗), 发芽盒水层深度5 cm]和对照[日均温5 °C:(12 h光照+12 h黑暗), 发芽盒水层深度3 mm]2个处理, 对供试品种已 催芽的种子培养处理10 d,处理结束后, 恢复到28 t条件下继续培养10 d,使种子恢复生长。测定成苗率、根长、根 数、苗高、单株鲜重、地上部鲜重和根鲜重, 通过隶属函数值分析和相关分析, 对其耐低温淹水能力进行综合评价和筛 选。 【结果】 25个水稻品种的成苗率胁迫系数存在明显差异, 变幅为0~1.00,平均胁迫系数为0.935。各指标胁迫系数 的相关分析结果表明, 成苗率与单株地上部鲜重呈显著正相关( P<0.05, 下同), 与其他性状也呈正相关, 但相关性未 达显著水平( P>0.05)。苗高与根长、地上部分鲜重和根鲜重呈极显著正相关( P<0.01), 与根数和株鲜重呈显著正相 关。根据隶属函数值将供试品种的耐低温淹水胁迫能力分为强、中、弱3种类型, 其中耐性强的品种有9个, 分别为桂 育12号、五山丝苗、优质农家种2号、桂育9号、金丝苗、象州香米、河西丰占、Y两优1号和桂育11号; 与耐性弱和耐性中 的水稻品种比较, 耐性强的水稻品种在根长、根数、根鲜重和苗高上有明显优势。与对照相比, 低温淹水胁迫下, 幼苗 的根长、根数、苗高、单株鲜重、地上部鲜重和根鲜重均有所降低, 其中根长降幅最大, 达19.0%, 其次是根鲜重和根 数, 降幅分别为18.2%和16.3%。 【结论】 成苗率、根系指标(根长、根数和根鲜重)和苗高可作为直播早稻耐低温淹水逆 境胁迫的关键筛选指标。桂育12号等9个品种可直接用于广西直播稻生产上, 也可为水稻耐低温淹水机理研究及培 育适合机直播的水稻品种提供材料。

SummaryThe development of high-yielding, short-duration super-rice hybrids is important for ensuring food security in China where multiple cropping is widely practiced and large-scale farming has gradually emerged. In this study, field experiments were conducted over 3 years to identify the yield formation characteristics in the shorter-duration (∼120 days) super-rice hybrid ‘Guiliangyou 2’ (G2) by comparing it with the longer-duration (∼130 days) super-rice hybrid ‘Y-liangyou 1’ (Y1). The results showed that G2 had a shorter pre-heading growth duration and consequently a shorter total growth duration compared to Y1. Compared to Y1, G2 had lower total biomass production that resulted from lower daily solar radiation, apparent radiation use efficiency (RUE), crop growth rate (CGR), and biomass production during the pre-heading period, but the grain yield was not significantly lower than that of Y1 because it was compensated for by the higher harvest index that resulted from slower leaf senescence (i.e., slower decline in leaf area index during the post-heading period) and higher RUE, CGR, and biomass production during the post-heading period. Our findings suggest that it is feasible to reduce the dependence of yield formation on growth duration to a certain extent in rice by increasing the use efficiency of solar radiation through crop improvement and also highlight the need for a greater fundamental understanding of the physiological processes involved in the higher use efficiency of solar radiation in super-rice hybrids.

Protein in rice grains is an important source of nutrition for rice consumers. This study mainly aimed to identify the critical factors that determine grain protein concentration in rice. Accumulation parameters, including mean accumulation rate (R-mean) and active accumulation duration (D-active), for protein and non-protein components and their correlations with protein concentration in rice grains were investigated in field experiments conducted over two years with six rice cultivars. Results showed that grain protein concentration ranged from 9.6% to 11.9% across cultivars and years. Accumulation processes of protein and non-protein components were well fitted by the logistic equation for all six rice cultivars in both years, and the ratio of protein to non-protein for R-mean and D-active ranged from 0.08 to 0.12 and 1.01 to 1.33, respectively. Grain protein concentration was significantly correlated with protein to non-protein ratio for R-mean. This study suggests that grain protein concentration is not solely determined by the accumulation of protein or non-protein component, but by the coordination of protein and non-protein accumulation.

High-temperature stress can cause serious abiotic damage that limits the yield and quality of rice. Heat tolerance (HT) during the flowering stage of rice is a key trait that can guarantee a high and stable yield under heat stress. HT is a complex trait that is regulated by multiple quantitative trait loci (QTLs); however, few underlying genes have been fine mapped and cloned. In this study, the F2:3 population derived from a cross between Huanghuazhan (HHZ), a heat-tolerant cultivar, and 9311, a heat-sensitive variety, was used to map HT QTLs during the flowering stage in rice. A new major QTL, qHTT8, controlling HT was identified on chromosome 8 using the bulked-segregant analysis (BSA)-seq method. The QTL qHTT8 was mapped into the 3,555,000–4,520,000 bp, which had a size of 0.965 Mb. The candidate region of qHTT8 on chromosome 8 contained 65 predicted genes, and 10 putative predicted genes were found to be associated with abiotic stress tolerance. Furthermore, qRT-PCR was performed to analyze the differential expression of these 10 genes between HHZ and 9311 under high temperature conditions. LOC_Os08g07010 and LOC_Os08g07440 were highly induced in HHZ compared with 9311 under heat stress. Orthologous genes of LOC_Os08g07010 and LOC_Os08g07440 in plants played a role in abiotic stress, suggesting that they may be the candidate genes of qHTT8. Generally, the results of this study will prove useful for future efforts to clone qHTT8 and breed heat-tolerant varieties of rice using marker-assisted selection.

[目的]筛选花期耐热性强、产量水平高的水稻品种,为水稻花期耐热性鉴定与评价及应对高温热害的品种选择提供理论依据和技术参考.[方法]在人工气候室内模拟高温胁迫(高温38℃,每天处理6 h,连续处理3 d),以Y两优1号为对照品种,以相对耐热指数为评价指标,同时结合产量水平,对100个不同水稻基因型的花期耐热性进行鉴定与评价.[结果]不同水稻基因型的花期耐热性差异明显,高温胁迫下颖花结实率为3.6％～64.3％,相对结实率为9.5％～80.0％.以相对耐热指数为评级标准,耐热性级别达到1(强)、3(较强)、5(中等)、7(较弱)和9(弱)级的水稻品种数量分别为4、13、42、26和15份.采用聚类分析法将100个基因型分为6种不同耐热性和产量水平的水稻类型,其中第一类在高温热害易发区推广种植安全生产性高.相对结实率是不同水稻基因型分类的主要因子,其次为产量,根据相对结实率和产量之间的二维象限分布特征,进一步筛选出耐热性较强、产量水平较高等综合性状好的品种.[结论]通过对100个不同水稻基因型花期耐热性进行鉴定和评价,筛选出特优837、云光14号、Q优8号、国稻7号、Y两优865、汕优63和黄华占等7个耐热性较强且产量水平较高的品种,这些品种可在高温易发区推广应用.

通过田间设置6个施氮水平,研究了不同施氮水平对优质杂交稻丰田优553的干物质生产、产量和氮肥利用率的影响.结果 表明,在一定施氮量范围内,丰田优553的产量随施氮量增加而增加,N180处理(180 kg/hm2)产量最高,达7.86 t/hm2,但施氮量超过180 kg/hm2后,产量略有下降,但差异不显著;与N0处理(不施氮对照)相比,施氮显著增加了丰田优553不同生育期的地上部生物量、拔节至抽穗和抽穗至成熟期干物质增加量,且抽穗后干物质增加量对产量贡献最大;施氮量为180 kg/hm2时,丰田优553的氮肥农学利用率(NAE)、回收利用率(NRE)和氮收获指数(NHI)均达到最大,分别为8.05 kg/kg、61.01％和56.12％;综合考虑产量与氮肥利用率,丰田优553的施氮量以180 kg/hm2为宜.

Biomass production and translocation, grain yield, and plant lodging resistance are interconnected in rice. In order to identify a feasible way to achieve both high grain yield and improved plant lodging resistance in rice, this study compared characteristics of biomass production and translocation, grain yield, and lodging resistance traits between rice crops grown in two years (2019 and 2020) with contrasting weather conditions (mainly different levels of daily solar radiation). Results showed that crop N uptake, crop growth rate, and biomass production were 12-21% higher during the pre-heading period but 20-45% lower during the post-heading period in 2019 compared to 2020. Translocation of pre-heading biomass to panicles was 68% higher in 2019 than in 2020. Stem and leaf sheath biomass at 0, 7, 14, and 21 days after heading and straw biomass at maturity were 10-32% higher in 2019 compared to 2020. Panicle-straw ratio at maturity was 10% lower in 2019 than in 2020. The difference in grain yield was not significant between 2019 and 2020. Plant lodging load was 173% higher whereas plant lodging index was 55% lower in 2019 compared to 2020. The results of this study suggest that improving lodging resistance while maintaining high grain yield can be achieved by promoting pre-heading growth in rice.

美国是水稻出口大国,水稻科研能力与生产水平位居世界前列.本文对美国特别是路易斯安那州的水稻生产和科研情况进行考察,目的是为了给国内水稻科研与生产提供参考及借鉴.路易斯安那州水稻种植面积在美国位居第3,达到17.20万hm2,种植的水稻类型分为长粒稻、中粒稻及特种稻,其中,长粒稻的种植面积最大,占89％;2019年水稻单产为7.15 t/hm2,总产达到119.78万t,总售价3.09亿美元.栽培管理技术先进,广泛使用洁田技术和机械化种植技术.高通量的分子标记辅助选择技术深度应用到水稻育种工作中.

Double-season rice cropping systems occupy a large portion of the rice production area in southern China. Because the problem of insufficient labor, mechanical transplanting (in contrast to the manual transplanting) was become more attractive in double-season rice system. However, the decisive yield factors which resulting in high grain yield of early-season rice are unclear under mechanical-transplanted conditions. In present study, the field experiments were conducted in the early season in 2017 and repeated in 2018 in Santang Town, Hunan Province, China. Ten early season rice cultivars (Zhuliangyou 819, Lingliangyou 268, Lingliangyou 104, Luliangyou 996, Xiangzaoxian 24, Xiangzaoxian 32, Xiangzaoxian 45, Xiangzaoxian 42, Zhongjiazao 17, and Zhongzao 39) were used as materials in this study. The difference in grain yield and closely-related agronomic and physiological traits of ten tested cultivars were compared. The range of yields (t ha(-1) at 86% dry matter) in 2017 was 6.2 to 8.7 (mean 7.8) and in 2018 was 6.5 to 8.4 (mean 7.8). Grain weight and pre-heading biomass accumulation had potent significant positive correlations with the grain yield. The greater pre-heading biomass accumulation was major attributed to higher apparent radiation use efficiency. Our results suggested that early-season rice cultivars to achieve the high grain yield in mechanical-transplanted conditions depends on apparent radiation use efficiency in the pre-heading period and higher grain weight.

[目的]对广西双季稻区直播生产中常用水稻品种的耐低温和耐低氧能力进行评价,筛选出适合早稻直播的耐低温低氧品种,为解决广西早造直播稻全苗难的问题提供理论参考.[方法]通过人工模拟低温(12、15和18℃)和低氧环境,对供试的22份水稻品种进行发芽试验,考察种子活力相关指标,通过变异系数、主成分分析和相关性分析等对其萌发活力进行综合评价.[结果]在低温和低氧条件下,不同品种的各项种子活力指标存在明显差异,耐低温、耐低氧能力不同,其中品种桂育9号、桂育11号、桂野丰、百香139、Y两优l号、中浙优8号、粤晶丝苗2号和优质农家种2的耐低温和耐低氧能力均较强.种子活力指标的变异系数分析结果显示,15℃低温条件下,发芽指数更具代表性;18℃低温条件下,苗干重、根干重和活力指数的代表性和灵敏性更强;低氧条件下胚芽鞘鲜重更具代表性.主成分分析结果表明,低温和低氧条件下各提取到3个和2个主成分,累计贡献率分别为85.643％和80.458％,低温条件下主要由18℃的活力指数、苗长、苗鲜重、苗干重、根长和根鲜重等指标决定,低氧条件下主要由缺氧反应指数决定.相关性分析结果显示,低氧条件下的直播性状与低温条件下的直播性状间无显著相关性(P＞0.05).[结论]通过对水稻直播性状指标进行综合分析,筛选出桂育9号等8个耐低温低氧的优良水稻品种,这些品种既可为直播生产提供服务,也为下一步水稻低温低氧相关基因的QTL定位和分子育种打下基础.