Mapping of QTLs for leaf developmental behavior in rice (Oryza sativa L.)

Leaf developmental behavior in rice (Oryza sativa L.) is one of the important agronomic characteristics, which not only determines vegetative growth but also influences grain yield. This study was conducted to identify quantitative trait loci (QTLs) for total number of leaves (TNL), days to the emergence of flag-leaf (DEF) and the leaf emergence rates (LER) on main stem, which mainly represent leaf developmental behavior, using recombinant inbred lines (RILs) derived from a cross between a japonica variety, Asominori and an indica variety, IR24, cultivated in 2001 and 2002. The transgressive segregations in both parental directions and continuous variations of all three tested traits were observed. Significant correlations among these traits were detected. A total of fourteen QTLs for leaf development behavior were detected with 289 RFLP markers. Six QTLs controlling TNL were mapped to chromosomes 3, 5, 6, 8, 9, 12, and accounted for 5.615.7% of the total phenotypic variations, and three QTLs for DEF were mapped to chromosome 3, 6, 8 and accounted for 10.735.4% of total phenotype variation and five QTLs for LER were mapped to chromosome 1(two QTLs), 2, 4, 9 and explained 6.217.5% of phenotype variation. The identification of QTLs for leaf developmental behavior in rice may be useful for selection of fast growing genotype before heading using maker-assisted selection.     

Effects of Night Temperature,Spikelet Position and Salicylic Acid on Yield and Yield‐Related Parameters of Rice (Oryza sativa L.) Plants

Periodic episodes of heat stress and seasonally high night temperatures (HNT) are predicted to occur more frequently in the current changing weather environment. These events affect aspects of crop growth and development, including oxidative‐stress damage, reducing crop yield and quality. Salicylic acid (SA), a naturally occurring phenolic compound, associated with thermo‐tolerance, prevents oxidative damage by detoxifying superoxide radicals and altering antioxidant capacity in plants. A study was conducted to determine the effects of HNT and SA on multiple rice yield‐determining parameters with special emphasis on effects of HNT and SA at different spikelet positions in the panicle. Plants were grown under ambient night temperature (27 °C) or HNT (32 °C) in the greenhouse. They were subjected to HNT through use of continuously controlled infrared heaters, starting from 2000 h to 0600 h. The HNT did not affect productive tillers, main‐stem panicle length or number of primary branches per panicle; however, reduced yield resulted from significant negative effects on spikelet fertility (SF), grain length and width. The grains located at the base of the panicle showed decreased fertility, length and width. Application of SA increased antioxidant capacity, thereby preventing damage to membranes, hence increasing yield by predominantly affecting SF in rice plants.     

Anther and pollen grain culture of rice (Oryza sativa L.)

Summary Factors favouring callus proliferation and subsequent regeneration of plants from pollen grains of rice anthers (Oryza sativa L., cvx. Bahia, Girona, Balilla × Sollana and Sequial) were determined. Cultivar differences in response were found, such as a high rate of haploid plant regeneration.In addition, isolated pollen grain culture was used to induce tissue proliferation outside the anther walls. The frequency of callus formation from isolated pollen grains was very low. It was necessary to preculture the anthers before pollen grain separation, in order to accomplish a successful development later. Root differentiation was observed in some of the obtained callus.     

Calcium silicate slag reduces drought stress in rice (Oryza sativa L.)

Silicon has been reported to reduce drought stress on many crops, but limited studies have evaluated this effect with rice using calcium silicate slag from the phosphorus fertilizer industry as a source of Si. A greenhouse study was performed to address this issue. Four slag rates (0, 1,000, 2,000 and 4,000 mg/kg) and two application methods (surface application and incorporation) were evaluated under two moisture regimes (flood and 50% field capacity) for drought stress mitigation in a mineral soil that is typical for rice production. Slag application significantly elevated plant‐available Si in the soil and Si accumulation in plant tissues, and tended to improve rice shoot and root biomass relative to the untreated control under both flooding and drought stress. Increased carbon isotope discrimination (△¹³C) and decreased proline in rice leaves subjected to drought stress indicate that this slag may reduce drought stress in rice, which was supported by restoration of foliage density, transpiration, photosynthesis rate and sugar accumulation to at or near flooded levels following the highest slag application. This study supports the usage of calcium silicate slag in rice production as it could improve Si availability and reduce drought stress.     

Effects of DEP1 on grain yield and grain quality in the background of two japonica rice (Oryza sativa) cultivars

Plant architecture is an accessible approach to achieving high-yield potential. The DENSE AND ERECT PANICLE 1 (DEP1) gene regulating panicle morphology, grain number per panicle, and nitrogen uptake and metabolism has been widely used for the breeding of high-yield rice in northern Chinese japonica varieties. However, there has been no consensus on the genetic effects of dep1 on grain yield and quality under different genetic backgrounds and growing environments. In the present study, we developed two sets of near-isogenic lines (NILs) of DEP1 (AKI-dep1, AKI-DEP1, LG5-dep1 and LG5-DEP1), each carrying the DEP1 region from either 'Liaogeng5' (LG5) or 'Akitakomachi' (AKI) in the AKI and LG5 backgrounds. Our results demonstrated that AKI-dep1/LG5-dep1 exhibited erect panicle and enhanced grain number per panicle, thereby consequently increasing grain yield, whereas they possessed inferior grain appearance compared with AKI-DEP1/LG5-DEP1 in the same background. However, the effects of dep1 on grain processing quality and eating and cooking quality varied with the background. These results provide useful information for high-yield erect panicle rice breeding by marker-assisted selection.     

Characterization of near-isogenic lines carrying QTL for high spikelet number with the genetic background of an indica rice variety IR64 (Oryza sativa L.)

Total spikelet number per panicle (TSN) is one of the most important traits associated with rice yield potential. This trait was assessed in a set of 334 chromosomal segment introgression lines (ILs: BC₃-derived lines), developed from new plant type (NPT) varieties as donor parents and having the genetic background of an indica-type rice variety IR64. Among the 334 ILs, five lines which had different donor parents and showed significantly higher TSN than IR64 were used for genetic analysis. Quantitative trait locus (QTL) analysis was conducted using F₂ populations derived from crosses between IR64 and these ILs. As a result, a QTL for high TSN (one from each NPT donor variety) was detected on common region of the long arm of chromosome 4. The effect of the QTL was confirmed by an increase in TSN of five near-isogenic lines (NILs) developed in the present study. The variation in TSN was found among these NILs, attributing to the panicle architecture in the numbers of primary, secondary and tertiary branches. The NILs for TSN and the SSR markers linked to the TSN QTLs are expected to be useful materials for research and breeding to enhance the yield potential of rice varieties.     

Chromosomal regions controlling anther culturability in rice (Oryza sativa L.)

Diallel analysis has revealed that anther culturability in rice (Oryza sativa L.) is a quantitative trait controlled by the nuclear genome. Mapping of anther culturability is important to increase the efficiency for green plant regeneration from microspores. In the previous study, we detected distorted segregation of RFLP markers in rice populations derived from the anther culture of an F₁ hybrid between a japonica cultivar ‘Nipponbare’ and an indica cultivar ‘Milyang 23’. To clarify the association between chromosomal regions showing distorted segregation and anther culturability, the anther culturability of doubled haploid lines derived from the same cross combination was examined, and the association between alleles of the RFLP markers, which exhibiting the most distorted segregation on chromosomes 1, 3, 7, 10 and 11, and the anther culturability was evaluated. One region on chromosome 1 was found to control callus formation from microspores, and one region on chromosome 10 appeared to control the ratio of green to albino regenerated plants. In both regions, the Nipponbare allele had positive effects. Three regions on chromosomes 3, 7 and 11, however, showed no significant effect on anther culturability. This revised version was published online in August 2006 with corrections to the Cover Date.     

Semidwarf gene sdk has pleiotropic effects on rice (Oryza sativa L.) plant architecture

Ideal plant architecture has become a significant objective in high‐yield rice breeding. In this study, a new semidwarf gene in sdk, a spontaneous dwarf mutant of ‘Kasalath’, was characterized and genetically mapped. The mutant has smaller panicles and seeds, reduced awns, and is 6–8 days earlier in heading than ‘Kasalath’. There was no significant difference in number (No.) of seeds and fertile seeds per panicle. Genetic analysis indicated that the dwarf character of sdk is controlled by a recessive gene, semidwarf k (sdk). From a segregating population of about 65 000 individuals, 4987 sdk‐type individuals were sampled. Gene sdk was located in a genomic region of 2622 kb flanked by markers R‐12 and R‐43 in the centromeric region of chromosome 2. The results provide an opportunity for gaining an understanding of the molecular mechanisms underlying sdk and opening possibilities for its use in rice breeding programmes.     

Association analysis of physicochemical traits on eating quality in rice (Oryza sativa L.)

Improvement of rice eating quality is an important objective in current breeding programs. In this study, 130 rice accessions of diverse origin were genotyped using 170 SSR markers to identify marker–trait associations with physicochemical traits on eating quality. Analysis of population structure revealed four subgroups in the population. Linkage disequilibrium (LD) patterns and distributions are of fundamental importance for genome-wide mapping associations. The mean r ² value for all intrachromosomal loci pairs was 0.0940. LD between linked markers decreased with distance. Marker–trait associations were investigated using the unified mixed-model approach, considering both population structure (Q) and kinship (K). In total, 101 marker–trait associations (p < 0.05) were identified using 52 different SSR markers covering 12 chromosomes. The results suggest that association mapping in rice is a viable alternative to quantitative trait loci mapping, and detection of new marker–trait associations associated with rice eating quality will also provide important information for marker-assisted breeding and functional analysis of rice grain quality.     

水稻叶片保绿相关性状的QTL分析

以籼稻窄叶青8号（ZYQ8）与粳稻京系17（JX17）为亲本的DH群体为材,考察叶片保绿相关性状,并利用该群体的分子连锁图谱进行QTL分析。共检测到7个与水稻叶片保绿有关的QTL,包括与黑暗下保绿面积相关的3个QTL,位于第1、6和8染色体上,贡献率分别为11.07%、10.31%和11.21%;与黑暗下保绿程度相关的2个QTL,位于第1和12染色体     

A major gene for low temperature germinability in rice (Oryza sativa L.)

Low temperature-induced retardation of seedling growth is a common problem in temperate rice-growing areas, at high altitudes of tropical and sub-tropical areas, and in areas with a cold irrigation water supply. Studies on low temperature germinability have revealed complex inheritance of the trait. The purpose of this study was to identify the gene(s) for low temperature germinability using Italica Livorno as a donor parent. The frequency distributions for the germination rate at 15 °C in the F₂ and BC₁F₁ populations showed continuous segregation, suggesting that low temperature germinability was under polygenic control. Since some lines in the BC₁F₁ population showed vigorous low temperature germinability similar to that of Italica Livorno, backcrosses until the BC₅F₁ generation was carried out using Hayamasari as the recurrent parent. Clear segregations of low temperature germinability were observed in the BC₅F₁ and BC₅F₂ populations. The distribution of low temperature germinability fitted a single-gene segregation, indicating that a single dominant gene with a large effect was transferred to Hayamasari. This gene is tentatively symbolized as Ltg(t). Low temperature germinability of near isogenic lines for Ltg(t) was similar to that of Italica Livorno. Ltg(t) should greatly contribute to the improvement and manipulation of low temperature germinability in rice breeding programs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic progress of upland rice (Oryza sativa L.) lines for disease resistance

The rice crop is affected by diseases throughout its cycle, impacting negatively on grain yield and quality. The control of the disease impact can be accomplished via crop breeding, using highly multiple resistant genotypes. This study aimed to evaluate the efficiency of multiple-character and specific selection of multiple resistance to major culture-associated diseases (neck blast, leaf scald and grain discoloration) in rice lines of the Upland Rice Genetic Breeding Program. The experiments were conducted in 35 sites during 12 agricultural years, where 124 lines were evaluated for the severity of fungal diseases, under natural field conditions. Multiple parameters were calculated based on the diseases´ scores: genetic, phenotypic and environmental variances, heritability, selection gain, renewal rate, and genetic and renewal progress. Genetic variance for the disease resistance was identified in the population, and the selection gain for multiple-character selection was of 3.16 year⁻¹ throughout the breeding process with a renewal rate of over 35%. The programme has showed efficiency in selecting multiple resistant genotypes to the mentioned diseases, highlighting genotypes with high potential for market release.     

水稻半外卷叶突变体sol1的表型分析与基因定位

适度卷曲有利于提高水稻叶片的光合效率,增加植株光合产物的有效积累量。我们利用甲基磺酸乙酯(EMS)处理籼型水稻保持系西农1B,获得一个稳定遗传的水稻半外卷叶突变体。该突变体从十叶期开始各叶片逐渐向外卷曲直至半卷状,并伴随茎秆半矮化和叶片披垂,暂被命名为semi-outcurved leaf 1 (sol1)。与野生型(WT)相比, sol1的叶片卷曲指数均达到30%以上(P<0.01);倒一、倒二、倒三、倒四节节间长度和穗长极显著缩短,倒一、倒二、倒三叶的叶夹角显著或极显著增加;有效穗数、千粒重、每穗实粒数、结实率显著或极显著下降,一次枝梗数则增加11.3%(P<0.05)。sol1的蒸腾速率、胞间CO2浓度、气孔导度显著高于野生型。石蜡切片显示, sol1倒一叶的泡状细胞体积变小,数量显著增多,表皮细胞体积略微增大。遗传分析表明, sol1的半外卷叶性状受1对隐性核基因调控,定位于6号染色体标记JY6-3和JY6-10之间165kb的物理范围内,共含15个注释基因。qRT-PCR结果表明,与泡状细胞相关的内卷基因和外卷叶基因RL14、Roc5、REL1在突变体sol1中呈...     

Inheritance of amylose content in rice (Oryza sativa L.)

Summary The inheritance of low and very low amylose contents in six rice crosses and their reciprocals was studied by single grain analysis of parents F₁, F₂, B₁ and B₂ seeds. To minimize the environmental effects, the seeds of all generations of all crosses were produced in a single season. The results indicated different dosage effects in different crosses. One major gene was found to govern a difference of 6–12% in amylose content in low and intermediate amylose parents. Very low amylose content was similarly found to be governed by one major gene in crosses between very low- and low-amylose content parents. Minor genes and modifiers also seem to play some role. In the cross between two low amylose parents differing by about 2.5% in amylose content, the differences appeared to be controlled by some minor genes and modifiers. The selection program in different crosses has been suggested.     

Breeding of widely compatible restorer lines in rice (Oryza sativa L.) through anther culture

Following anther culture of various F₁ hybrids of indica restorer (R) lines/wide compatible varieties (WCVs) and japonica R lines/WCVs, the homozygous diploid plants (2n) generated were test-crossed with indica WA type cytoplasmic-genetic male sterile (CMS) line Zhanshan 97A (WA), indica testers Nanjing 11 and Nante, japonica BT CMS line Hanfeng A (BT), and japonica testers Balilla and Akihikari to identify widely compatible restorer lines. The results of this study showed that among the diploid pollen plants generated from F₁ hybrids of indica R lines/WCVs, 36.7% and 64.7% possessed normal fertility restoration ability (rate of seed-setting > 80%) to Hanfeng A and Zhanshan 97A, respectively. 71.3% and 32.3% had normal fertility restoration ability to Hanfeng A and Zhanshan 97A, respectively, in diploid pollen plants derived from the japonica R lines/WCVs F₁'s anther culture. Several widely compatible R lines were selected from anther culture of F₁ hybrids of indica R lines/WCVs and japonica R lines/WCVs. These widely compatible R lines derived from diploid pollen plants showed good wide compatibility and restoration ability both to WA and BT type CMS lines. Strong standard heterosis of major agronomic traits and yield traits was observed in F₁ test-crosses of widely compatible R lines with Hanfeng A and Zhanshan 97A. The wide compatibility in widely compatible R lines H17, H158 and H281 was studied by a set of three-way crosses. Segregation of the fertile plants with seed-setting rate > 70% and semi-fertile plants with seed-setting rate > 69.9% agreed with a ratio of 1:1, indicating that wide compatibility in these widely compatible R lines is governed by a pair of major genes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic analysis of semidwarf mutants induced in indica rice (Oryza sativa L.)

The mode of inheritance of five semidwarf (SD) mutants and allelic relationship with DGWG (sd1) locus was studied. The five SD mutants viz., Basmati 370 (SD1), Basmati 370 (SD2), Basmati 370 (SD3), TCA 2 (SD) and TCA P2-5 (SD) when crossed with their tall parents exhibited monogenic inheritance of 3 tall: 1 semidwarf in the F2 progenies. The SD mutants were also crossed with semidwarf varieties (DGWG and Bala) possessing sd1 gene. Crosses between Basmati 370 (SD1) × Bala, Basmati 370 (SD3) × Bala and TCA 2 (SD) × DGWG produced tall F1 hybrids and in F2 generation, modified dihybrid ratios (9 : 6 : 1 and 9 : 7) were observed indicating that the mutants Basmati 370 (SD1), Basmati 370 (SD3) and TCA 2 (SD) are non-allelic to sd1 gene. Whereas, the mutants Basmati 370 (SD2) and TCA P2-5 (SD) when crossed with Bala produced semidwarf F1 hybrids and in F2 generation, segregation for plant height was not observed indicating that these mutants are allelic to sd1 gene. The three non-allelic SD mutants identified in the present study can be used in rice breeding as alternative gene sources for semidwarfism. This revised version was published online in July 2006 with corrections to the Cover Date.     

籼粳交稻米品质性状杂种优势的遗传分析

用胚乳性状遗传模型和分析方法对籼粳交稻米品质性状的杂种优势进行了遗传分析,结果表明：各品质性状都具有一定的杂种优势,其中碱消值和蛋白质含量的优势较强。直链淀粉含量和胶稠度的优势较弱。不同性状杂种优势的遗传原因不同,直接显性和母体显性对杂种优势的贡献大小因性状而异,但总的来说,母体显性对籼粳杂种Ｆ２籽粒品质性状的杂种优势具有重要的意义,细胞质效应对部分性状（如胶稠度、蛋白质含量）的群体平均优势有一定     

施氮水平和栽插密度对天优华占生长和产量及产量构成因子影响

摘 要：天优华占由中国水稻研究所等多家科研单位选育而成新品种,米质优良,达到国家一级标准。因而,对于天优华占最佳氮肥用量和种植密度的研究及其高产机理的探讨,可为该品种在金华地区的大面积推广提供理论支持。以晚稻天优华占为材料,研究不同氮肥用量(0、120、165、210kg/hm2)和栽插密度(22.5万/hm2和16.5万/hm2)对水稻产量的影响,探索其最佳的栽培方式。结果表明：不同栽插密度下,不同施肥水平间天优华占产量水平差异较大。两种栽培密度下,天优华占的产量都随着氮肥用量的增加而增加。相同施氮水平,以高密度处理产量较高。高密度和低密度下,均以高肥区产量水平最高,分别达到7 464.3、6 534.8 kg/hm2。通过此研究发现,天优华占最佳栽插密度为22.5万/hm2,每1 hm2施用氮肥210 kg比较适宜。     

Tagging quantitative trait loci associated with grain yield and root morphological traits in rice (Oryza sativa L.) under contrasting moisture regimes

Plant breeding for drought-prone habitats envisages a favorable combination of grain yield and drought resistance. Though several components enhancing drought resistance have been identified in rice,their association with grain yield, under low-moisture stress, has been established in very few instances. We attempt to study the associations between rice grain yield and root system parameters both at phenotypic and genotypic levels. The doubled haploid population of IR64/Azucena was evaluated for root related traits at peak vegetative stage and grain yield related traits under both low-moisture stress and non stress conditions. ‘Mean environment’ was computed for yield related traits. Correlation and QTL mapping was attempted to find out the associations. The correlation between maximum root length and grain yield was positive under stress and negative in non stress. Genotypes with thicker and deeper roots, manifested higher biomass and grain yield under stress. Only one QTL found to increase days to flowering in non stress was also found to influence root volume and dry weight negatively under stress. The study suggests that loci enhancing grain yield and related traits were not pleiotropic with loci for desirable root morphological traits studied under low-moisture stress at vegetative stage, in the genetic material used in the study. It is thus possible to combine higher grain yield and desirable root morphological traits, favorably, to enhance productivity of rice under low-moisture stress. In rainfed ecologies, where deep roots contribute to enhanced drought resistance in rice, the results indicate the possibility of combining drought resistance with higher levels of grain yield. This revised version was published online in August 2006 with corrections to the Cover Date.