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10 July 2019, Volume 33 Issue 4 Previous Issue    Next Issue
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Reviews and Special Topics

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High Efficiency is a Dominant Target for Current Rice Breeding Guoying XIAO, Youlun XIAO, Jinjiang LI, Lihua DENG, Lüshui WENG, Qiucheng MENG, Jianghui YU 2019, 33(4): 287-292.  DOI: 10.16819/j.1001-7216.2019.8117 Abstract ( )   HTML ( )   PDF (381KB) ( )   The socioeconomic development and decreases of relative benefits in rice production shift the dominant target of breeding from mainly seeking high yield potential to high efficiency in whole cycle in rice. The high efficiency breeding mainly consists of three aspects. The first is high efficiency technology in rice breeding. The molecular marker and gene chip technology can improve selection efficiency of elite genotypes, and the gene editing technology can efficiently create excellent allelic variations, as well as the transgenic technology can transfer outstanding characters cross species barriers. All of them are good approaches to raise breeding efficiency in rice. The second is high efficiency in productive characters of rice. High yield, environment-friendliness, and salubrity is basis for achieving high returns, and the good grain quality is a multiplier to increase per unit output benefit, then multiple resistances are a divisor to reduce the cost of each bushel, as well as the early maturity can ensure two cropping in one year. Only integration of the elite productive characters in one variety can realize the high efficiency output in each acre. The third is high efficiency in farming characters of rice. The direct seeding of rice in double cropping system is an efficient farming technique that requires rice to possess advantageous farming characters, such as cold tolerance at seedling and heading stages, anaerobic germination, and submergence tolerance. Chemical weeding demands herbicide resistance, and mechanical harvesting needs lodging resistance and good seed holding. Only rice with these efficient farming characters can achieve high efficiency tillage in rice production. Overall, high efficiency is a dominant target for current and future rice breeding.

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Effects of Main Water-saving Irrigation Methods on Morphological and Physiological Traits of Rice Roots Tingting LI, Yufeng FENG, An ZHU, Jian HUANG, Hao WANG, Siyu LI, Kun LIU, Rumeng PENG, Honglu ZHANG, Lijun LIU 2019, 33(4): 293-302.  DOI: 10.16819/j.1001-7216.2019.8116 Abstract ( )   HTML ( )   PDF (705KB) ( )   Rice is the most water-consuming crop. The development of water-saving cultivation is of great significance for efficient utilization of water and alleviation of water shortage in China. Roots are an important part of rice plants and involved in acquisition of nutrients and water, synthesis of plant hormones, organic acids and amino acids. Water management methods could exert an influence on root growth and development directly or indirectly, as well as the growth and development of above-ground part of plants and yield formation of rice. We reviewed the effects of main water-saving irrigation methods, including alternate wetting and drying irrigation, controlled irrigation and dry cultivation, on the morphological and physiological characteristics of rice roots. We also put forward some research priorities on the effect of water-saving irrigation on rice roots in the future to lay a theoretical basis for improving the morphological and physiological characteristics of rice roots, high yielding and water saving in rice cultivation.

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Research Progress of Soil Nitrogen Priming Effect and Its Microbial Mechanisms Shaowen LIU, Min YIN, Guang CHU, Chunmei XU, Danying WANG, Xiufu ZHANG, Song CHEN 2019, 33(4): 303-312.  DOI: 10.16819/j.1001-7216.2019.8091 Abstract ( )   HTML ( )   PDF (872KB) ( )   The soil nitrogen priming effect is the key mechanism in the process of soil nutrient release and plant nutrient absorption. The insight into soil priming effect will not only help make more reasonable nitrogen fertilizer operations in agricultural production, thus improving the utilization rate of nitrogen fertilizer, but also conduces to the assessment and control of environmental pollution, so as to provide effective pollution control methods. On the basis of the introduction of the concept and mechanism of soil nitrogen priming effect, we introduce the prevailing determination methods of the current nitrogen priming effect and its advantages and disadvantages of practical application. The effects of exogenous additives (inorganic nitrogen fertilizer, organic materials and root exudates) on soil nitrogen stimulation and their microbial mechanisms were emphatically expounded. The effect of exogenous additives on soil C/N ratio may be the key factor to soil nitrogen stimulation. When available C is redundant, the application of inorganic nitrogen fertilizer promotes the decomposition of soil organic nitrogen, thus showing a positive priming effect. On the contrary, when available C is insufficient but available N is enriched, the activity of nitrogen-fixing microorganisms is relatively enhanced, which results in a negative priming effect. Microorganisms are the promoters of priming effects. We also analyzed the possible mechanism of microorganisms in the process of soil nitrogen stimulation through three theoretical hypotheses: 1) co-metabolism theory; 2) microbial hotspots; 3) microbial energy and material transformation theory. Through the discussion, we can deepen the understanding of the priming effect, and provide an effective way to further clarify the microbial mechanism of the soil priming effect, the interaction effect between factors and the improvement of nitrogen use efficiency through the priming effect.

Research Papers

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Orientation Improvement of Blast Resistance in Rice via CRISPR/Cas9 System Peng XU, Hong WANG, Ranran TU, Qunen LIU, Weixun WU, Xiumin FU, Liyong CAO, Xihong SHEN 2019, 33(4): 313-322.  DOI: 10.16819/j.1001-7216.2019.9043 Abstract ( )   HTML ( )   PDF (1334KB) ( )   【Objective】 CRISPR/Cas9 gene editing is an effective biotechnology for crop genetic improvement. This study aims to edit Pita, Pi21 and ERF922 genes for obtaining valuable and stable genetic materials with resistance to rice blast. 【Method】The target genes Pita, Pi21 and ERF922 were selected for constructing the pC1300-2×35S::Cas9-gPita-gPi21-gERF922 expression vector by CRISPR/Cas9 gene editing technology, and transformed by Agrobacterium-mediated method into long-grain japonica rice restore lines L1014. Stable genetic mutant lines were selected and their resistance to rice blast was identified. 【Result】 In the T0 transgenic lines, the mutation rates of Pita, Pi21 and ERF922 were 75%, 85% and 65%, respectively, and most of the mutant lines are biallelic mutations. The homozygous mutation lines without T-DNA components within the screened T1 were selected and transferred to T2 stably. Evaluation analysis of resistance to rice blast suggested that the mutant lines showed significantly higher resistance to M. oryzae compared with the wild type. The expression level of defense-related genes involved in signaling pathways of salicylic acid, jasmonic acid and ethylene metabolisms was up-regulated in the mutant lines compared to the wild type after inoculation of the physiological races of M. oryzae. Therefore, we hypothesized that the increased resistance of homozygous mutant lines to rice blast might be related to the activation of the response to M. oryzae. 【Conclusion】The homozygous mutant lines with stable inheritance and high blast resistance were obtained by CRISPR/Cas9 system, which would provide ideal materials for improving blast resistance in rice.

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Identification and Genetic Analysis of Split Husk Mutant sh1 in Rice Xiaowu PAN, Wenqiang LIU, Yongchao LI, Haibo XIONG, Xinnian SHENG, Yonghong DUAN, Yaying YU, Wenjin ZHAO, Xiucai WEI, Xiaoxiang LI 2019, 33(4): 323-330.  DOI: 10.16819/j.1001-7216.2019.9027 Abstract ( )   HTML ( )   PDF (918KB) ( )   【Objective】The objective of the research is to identify and clone a rice split-husk gene, providing support for elucidating the genetic mechanism of rice floret closing. 【Method】A split husk mutant, sh1, was isolated from an ethylmethylsulfone (EMS) mutagenic population of indica cultivar Xiangzaoxian 6. The morphological characteristics of florets and lodicules were observed. The SH1 gene was identified by map-based cloning using an F2 population of a cross between sh1 and 02428. In addition, expression levels of related genes were analyzed by quantitative PCR. 【Results】The sh1 mutant showed normal floral morphological characteristics, but failed to close the lemma and palea after floret opening, which was caused by delay of lodicule dehydration. The sh1 mutant was also featured by increased number of effective panicles, obviously decreased seed-setting rate and 1000-grain weight. Genetic analysis indicated that the mutant phenotype was controlled by a pair of recessive nuclear gene. The SH1 gene was fine-mapped to a 110 kb interval between markers ID19827 and ID19884 on the chromosome 3. After sequencing of this region, we found that there is a single base transition in the coding region of allene oxide synthase 1 (OsAOS1), which resulted in an amino acid substitution. Correspondingly, the mutant showed reduced content of jasmonic acid (JA) and differential expression of genes related to JA synthesis and signal transduction. 【Conclusion】The SH1 gene regulates rice floret closing through JA synthesis and signal transduction, and OsAOS1 is the candidate gene for SH1.

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Genomic Prediction of Combining Ability for Agronomic Traits in Rice Based on NCII Design Xin WANG, Ying MA, Zhongli HU, Chenwu XU 2019, 33(4): 331-337.  DOI: 10.16819/j.1001-7216.2019.9025 Abstract ( )   HTML ( )   PDF (907KB) ( )   【Objective】It plays a key role in hybrid rice breeding to select hybrids with high specific combining ability based on high general combining ability of parental inbred lines. Genomic selection that is based on molecular markers across the whole genome and phenotypes of samples enable us to establish prediction models and achieve more reliable selection of varieties. 【Method】We investigated the genomic predictive ability of combining ability for agronomic traits in rice based on NCII design. And the effects of different training population construction methods on predictive ability of hybrid performance were compared. 【Result】The predictive abilities of general combining ability for eight agronomic traits, ranged from 0.3888 to 0.7367, were dominated by their heritability. The predictive ability of specific combining ability for hybrids was lower, but the ability of directly predicting phenotypes for hybrids was higher. 【Conclusion】The genomic prediction of combining ability for rice parental lines is effective and can help breeders to select parents effectively. With regard to hybrid selection, direct predicting phenotypes of hybrids is the most effective method. At this time, allowing more parents to participate in the crosses for hybrid training set in a balanced way is benefical to obtain higher predictive ability.

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Responses of Rice Appearance and Processing Quality to Elevated Atmospheric CO2 Concentration Dongming WANG, Ye TAO, Jianguo ZHU, Gang LIU, Chunwu ZHU 2019, 33(4): 338-346.  DOI: 10.16819/j.1001-7216.2019.8134 Abstract ( )   HTML ( )   PDF (1017KB) ( )   【Objective】Rice appearance and processing quality will be reduced by elevated atmosphere CO2 concentration ([CO2]). To ascertain the mechanism behind this decline and then alleviate it, 【Method】we used a Free-air Carbon Dioxide Enrichment (FACE) facility, two kinds of cultivars and its three kinds of genetically modified materials (Zhonghua 11 and its transpiration-promoting genetic materials, ZmK2.1-15, ZmK2.1-20, OsKAT3-26, OsKAT3-30; Zhonghua 11 and its crown root-promoting genetic materials, ERF3-7 and ERF3-12; Nipponbare and its nitrate absorption-promoting genetic material, NIL) to study the responses of appearance and processing quality of different rice genetic materials to elevated [CO2]. 【Results】The responses of rice appearance and processing quality to elevated [CO2] varied among these genotypes. The chalky grain percentage and chalkiness degree of Zhonghua11 increased by 9.2% and 4.4% under elevated [CO2] compared with ambient [CO2], and head rice percentage decreased by 5.3%, while the chalky grain percentage and chalkiness degree of Nipponbare decreased by 11.1% and 7.9%, and head rice percentage increased by 9.8%. Transpiration-promoting genetic materials significantly mitigated the negative effect of elevated [CO2] on the appearance and processing quality of Zhonghua11. As compared with ambient [CO2], the changes in chalky grain percentages for ZmK2.1-15, ZmK2.1-20, OsKAT3-26 and OsKAT3-30 under elevated [CO2] were -2.7%, -16.3%, -14.8%, +7.4%, and that of chalkiness degree was -8.7%, -22.3%, -15.1%, -3.0%, and that of head rice percentage was +2.1%, +6.4%, +3.6%, -7.0%. Crown root-promoting genetic materials exacerbated the negative impact of elevated [CO2] on the appearance and processing quality of Zhonghua 11, with the chalky grain percentage increased by 17.7% and 11.5% under elevated [CO2], and the chalkiness degree increased by 34.4% and 19.1%, head rice percentage decreased by 10.1% and 0.8%, respectively. The chalky grain percentage and chalkiness degree of nitrate absorption-promoting material (NIL) did not change significantly at elevated [CO2], and the head rice percentage decreased by 4.2%. The appearance quality of NIL was significantly improved as compared with that of Nipponbare, with the chalky grain percentage and chalkiness degree decreased by 16.5% and 17.9% under elevated [CO2], and 26.3% and 28.9% under ambient [CO2]. 【Conclusion】The promotion of transpiration and nitrate absorption through genetic regulation could be one of the effective ways to improve the appearance and processing quality of rice under elevated [CO2] in the future.

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Effects of Nitrogen Application on Rice Photosynthetic Characteristics, Nitrogen Uptake and Grain Yield Formation Under Rainfall-adapted Water Management Jun YAN, Qixia WU, Jianqiang ZHU, Luping ZHANG 2019, 33(4): 347-356.  DOI: 10.16819/j.1001-7216.2019.8140 Abstract ( )   HTML ( )   PDF (873KB) ( )   【Objective】The research aims to make rational use of rainfall during rice growth, improve paddy nitrogen fertilizer management practice in the Jianghan Plain.【Method】The field plot experiment with two irrigation regimes (conventional flooding irrigation, FI; rainfall-adapted irrigation, RAI) and three nitrogen fertilizer managements (farmers’ fertilization practice, FFP; 30% urea+70% controlled release compound fertilizer, 30%N+70%CRF; optimized and reduced nitrogen fertilizer application, OPT-N) were carried out to study the effects of water and fertilizer managements on rainfall utilization rate, rice yield, photosynthetic characteristics, dry matter accumulation and nitrogen uptake and utilization.【Result】1) Compared with FI, RAI reduced the irrigation quantity by 41.7%, economized water resources while improved the ability of paddy to saving and utilizing rainfall, net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci) and transpiration rate (Tr), dry matter accumulation, nitrogen absorption and grain yield in varying degrees during rice growth. 2) Compared with FFP treatment under two water management modes, OPT-N significantly decreased Pn, Gs, Ci, Tr, dry matter accumulation and nitrogen uptake of rice at tillering stage, but increased the above-mentioned indexes from booting to filling stages, but had little effect on final yield formation. 3) RAI combined with 30% N + 70% CRF treatment helped increase Pn, Gs, Ci and Tr in the early growth stage, and promoted the accumulation of dry matter significantly in the middle and late growth stages. The nitrogen uptake was significantly higher than in OPT-N and FFP during the tillering stage, and was significantly higher than FFP at the full heading stage and mature stage. Effective panicle number, panicle length, 1000-grain quality and seed setting rate were the highest among treatments, and the actual yield was 10.4% higher than that in conventional water and fertilizer management.【Conclusion】Under the rainfall-adapted irrigation, OPT-N had no significant effect on rice growth and yield, 30% N+70% CRF was helpful to increase photosynthesis, nitrogen uptake and yield of rice.

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Effect of Interaction Between Nitrogen Rate and Irrigation Regime on Grain Quality of japonica Rice in Northeast China Chanchan ZHOU, Yuancai HUANG, Baoyan JIA, Yan WANG, Ruifeng LI, Shu WANG, Yue FENG, DOU Fugen 2019, 33(4): 357-367.  DOI: 10.16819/j.1001-7216.2019.9014 Abstract ( )   HTML ( )   PDF (1153KB) ( )   【Objective】The objective of this study is to elucidate the effects of nitrogen rates and irrigation regimes and their interactions on grain quality of rice. 【Method】Two rice cultivars, Shendao 47 (an inbred japonica cultivar) and Jingyou 586 (a hybrid japonica combination), were grown in pots. Four irrigation regimes, continuous flooded (CF), shallow-wet irrigation (SWI), alternate wetting and moderate drying (WMD) and alternate wetting and severe drying (WSD), and two nitrogen (N) rates, normal amount of N (NN, 180 kg/hm2), and high amount of N (HN, 220 kg/hm2), were designed during the whole growing season. 【Result】The interactions between N rates and irrigation regimes significantly affected grain quality of rice. The milling quality, appearance quality, nutrition quality and cooking and eating quality were better under WMD regime regardless of N rate. Under the NN treatment, the WSD regime decreased head rice rate, gel consistency, the peak viscosity and breakdown but increased the percentage of chalky grain and chalkiness, amylose content and setback as compared with the CF regime. Under the HN treatment, the grain quality of rice was slightly better under the WSD regime than under the CF regime, however, the differences in grain quality between the two irrigation regimes were not significant. The effects of irrigation regimes on total amino acid concentrations varied with N rates and cultivars. Under the NN rate, the WMD regime increased the total amino acid concentrations of both rice cultivars; under the HN rate, the WSD regime significantly increased the total amino acid concentrations of Shendao 47, while Jingyou 586 had higher total amino acid concentrations, and the concentrations of essential and non-essential amino acids followed the same trend as those of total amino acids. 【Conclusion】The WMD improved grain quality of the rice cultivars. To achieve high rice quality, the combinations between WMD and NN, and between WMD and HN were recommended for inbred rice Shendao 47 and hybrid rice Jingyou 586, respectively.

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Distribution Characteristics of Echinocloa Species in Rice Fields in China: A Case Survey on 73 Sites from Nine Provincial Administrative Regions Guoqi CHEN, Wei TANG, Jun LI, Yongliang LU, Liyao DONG 2019, 33(4): 368-376.  DOI: 10.16819/j.1001-7216.2019.8137 Abstract ( )   HTML ( )   PDF (895KB) ( )   【Objective】The purpose is to disclose the distributon patterns of Echinocloa species in rice fields in China. 【Method】In periods from September to November between 2015 and 2018, we conducted field surveys on the occurrence of Echinocloa species at 73 locations (totally 525 rice fields). 【Result】Totally eight Echinocloa species were observed in the 525 fields surveyed. Among these fields, E. crusgalli var. mitis showed the highest frequency (55.43%), followed by E. glabrescens (47.28%), E. crusgalli var. crusgalli (40.40%), E. crusgalli var. zelayensis (20.94%); and E. caudata, E. oryzoides, E. cruspavonis, E. colona showed low frequency. On rice fields surveyed in Northeast China, E. oryzoides was mono-dominant among Echinocloa species on rice fields; in East China, E. glabrescens and E. crusgalli var. mitis were the most serious among this genus, E. crusgalli var. crusgalli and E. crusgalli var. zelayensis also showed high occurrences; in South China, E. crusgalli var. crusgalli was mono-dominant; in Northwest China, E. crusgalli var. mitis and E. crusgalli var. crusgalli were dominant; and in Southwest China, E. crusgalli var. mitis was dominant and E. crusgalli var. crusgalli also showed high occurrence. Among the eight Echinocloa species observed, E. crusgalli var. mitis showed the highest niche breadth (35.2), followed by E. glabrescens (23.6), E. crusgalli var. zelayensis (18.2) and E. crusgalli var. crusgalli (16.3). Niche overlaps among E. glabrescens, E. crusgalli var. zelayensis and E. crusgalli var. mitis were high, as well as those between E. crusgalli var. crusgalli and E. cruspavonis, E. colona or E. caudata, respectively.【Conclusion】Frequency of Echinocloa species varied with areas, and the relative mechanisms entail further studies.

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Genetic Analysis of Rice Neck Blast Resistance in Huang-Huai-Hai Region Yan LIU, Baoxiang WANG, Bo YANG, Tingmu CHEN, Yungao XING, Zhiguang SUN, Bo XU, Ming CHI, Baiguan LU, Jian LI, Jinbo LIU, Zhaowei FANG, Derong QIN, Dayong XU 2019, 33(4): 377-382.  DOI: 10.16819/j.1001-7216.2019.8104 Abstract ( )   HTML ( )   PDF (696KB) ( )   【Objective】 To identify the rice blast resistance and the genotype of rice varieties in Huang-Huai-Hai Region, 【Method】the rice blast resistance of the rice varieties collected from five districts of this region was identified for two consecutive years through artificial injection and natural induction in rice blast nursery. The genotypes were analyzed with the functional markers of Pita, Pib, Pi54 and Pikm. And the cluster analysis was carried out according to the rice blast resistance level. 【Result】 85.2% and 65.9% of the tested varieties were sensitive to rice blast through artificial identification and the blast nursery identification, respectively. 84% and 65% of the tested varieties carry Pi54 and Pib, respectively. But the cluster analysis result showed that Pi54 and Pib have low contribution rate of rice blast resistance in this region.【Conclusion】 The rice varieties in the region have low resistance to rice blast, as these genes confer weaker or lost resistance to rice blast. It is crucial to screen new resistant varieties and utilize new resistant genes for breeding.