Chinese Rice Cultivars Research Articles

Effects of submergence stress at the vegetative growth stage on hybrid rice growth and grain yield in China

Submergence stress can greatly limit grain yield of inbred rice (Oryza sativa L.), but the effects of submergence on hybrid rice are unclear. A pot experiment was conducted to clarify the effects of submergence that happens at the vegetative growth stage on two Chinese hybrid rice cultivars. The rice cultivars Zheyou-18, an indica-japonica hybrid, and Yliangyou-689, an indica hybrid, were planted under two treatments, submergence (43 cm depth of tap water for about 2 wk) and control (no submergence). Results showed that the grain yield of submerged ‘Yliangyou-689’ was 539.0 g m-2 in 2018 and 614.2 g m-2 in 2019; submergence significantly reduced grain yield by 49.6% and 44.2% of that of the control. The lower level of grain yield was attributed to reduced survival rate, numbers of tillers and spikelets, plant dry weight, and crop growth rate, and excessive elongation of stems due to submergence of plants. The grain yield of submerged ‘Zheyou-18’ was 466.8 g m-2 in 2018 and 376.4 g m-2 in 2019 and neither of which were significantly different from that of the control, indicating higher submergence tolerance in ‘Zheyou-18’ than in ‘Yliangyou-689’. Submergence did not affect plant N and K contents, but it reduced plant N uptake rates by 47.8% to 88.7% and it reduced K uptake rates by 53.9% to 89.5% of that of the control in these two hybrid cultivars. Furthermore, nonsignificant differences were observed in all of the parameters related to rice starch viscosity between control and submergence treatment.

Divergence in response of japonica and hybrid rice to titanium dioxide nanoparticles

The present study aimed to compare the responses of two rice cultivars to titanium dioxide nanoparticles (nTiO2), in plant performance and root-associated soil microbes, and provide a reference for the selection of nanoparticle-responsive varieties. The field experiment was conducted to study the effects of nTiO2 (applied at 200 mg/kg) on typical Chinese rice cultivars, Wuyunjing23 (WYJ23) and Yongyou2640 (YY2640), for the whole life cycle. We evaluated agronomic and physiological parameters including chlorophyll content and antioxidant enzyme activities at the heading stage, and biomass, Ti, and nutrient elements uptake after harvest. Soil bacterial communities were also measured through 16S rRNA gene sequencing. Exposure to nTiO2 led to neither Ti accumulation nor changed biomass in either cultivar, but it increased root Fe uptake and reduced grain Cu content. Specifically, nTiO2 exposure decreased the chlorophyll content but increased the peroxidase activity in WYJ23; such altered physiology might affect root exudates and further modify bacterial communities. Although nTiO2 did not induce visible phytotoxicity in YY2640, it affected the abundance of bacteria genera associated with N turnover and plant-C-metabolizing (e.g., Geobacter and Gaiella), resulting in changed C and N cycling in the rhizosphere. This study revealed divergent responses of WYJ23 and YY2640 to nTiO2, both in plant physiology and rhizosphere system. nTiO2 induced greater physiological response but affected the rhizosphere little in WYJ23. By contrast, nTiO2 changed soil microbes and enzyme activities without affecting the physiology of YY2640, suggesting its superior adaptivity to nTiO2.

Genomic atlases of introgression and differentiation reveal breeding footprints in Chinese cultivated rice

The long history of cultivation and breeding has left a variety of footprints in the genomes of Asian cultivated rice (Oryza sativa L.). In this study, we focus on two types of genomic footprints, introgression and differentiation, in a population of more than 1200 Chinese rice accessions. We found that a Xian/indica and a temperate Geng/japonica accession respectively contained an average of 19.3-Mb and 6.8-Mb alien introgressed chromosomal segments, of which many contained functional sequence variants, quantitative trait loci, or genes controlling flowering, grain, and resistance traits. Notably, we found most introgressions, including the known heterotic loci Hd3a and TAC1, were distributed differentially between the female and male parents of three-line indica hybrid rice, indicating their potential contribution to heterosis. We also found many differentiated regions between subgroups within a subpopulation contained agronomically important loci, such as DTH7, Hd1 for heading date, and qCT7 for cold tolerance, providing new candidates for studying local adaptation or heterosis. Tracing these footprints allows us to better understand the genetic exchange or differentiation underlying agronomic traits in modern Chinese rice cultivars. These findings also provide potential targets for rice genetic research and breeding.

Analysis of genetic architecture and favorable allele usage of agronomic traits in a large collection of Chinese rice accessions.

Genotyping and phenotyping large natural populations provide opportunities for population genomic analysis and genome-wide association studies (GWAS). Several rice populations have been re-sequenced in the past decade; however, many major Chinese rice cultivars were not included in these studies. Here, we report large-scale genomic and phenotypic datasets for a collection mainly comprised of 1,275 rice accessions of widely planted cultivars and parental hybrid rice lines from China. The population was divided into three indica/Xian and three japonica/Geng phylogenetic subgroups that correlate strongly with their geographic or breeding origins. We acquired a total of 146 phenotypic datasets for 29 agronomic traits under multi-environments for different subpopulations. With GWAS, we identified a total of 143 significant association loci, including three newly identified candidate genes or alleles that control heading date or amylose content. Our genotypic analysis of agronomically important genes in the population revealed that many favorable alleles are underused in elite accessions, suggesting they may be used to provide improvements in future breeding efforts. Our study provides useful resources for rice genetics research and breeding.

A study on volatile metabolites screening by HS‐SPME‐GC‐MS and HS‐GC‐IMS for discrimination and characterization of white and yellowed rice

AbstractBackground and objectivesYellowed rice results in serious economic losses to grain industry. This study attempted to profile the volatile metabolites in before‐ and after‐yellowing rice of five Chinese common rice cultivars. Application untargeted metabolomics approach to discover the biomarkers in yellowed rice.FindingsThe volatile metabolites were detected by headspace‐gas chromatography–ion mobility spectrometry (HS‐GC‐IMS) and headspace solid‐phase microextraction–gas chromatography‐mass spectrometry (HS‐SPME‐GC‐MS). Yellowed rice emitted more aldehydes, alcohols, furan, and less ester than white rice. Partial least squares‐discriminant analysis (PLS‐DA) based on GC‐MS and GC‐IMS data was revealed a good classifying tool for white and yellowed rice. Hexanal, nonanal, octanal, 1‐pentanol, and 2‐pentyl‐furan were selected as the potential markers by the variable importance in projection (VIP) variable selection method. All of these markers were associated with fatty acid oxygenation.ConclusionsComparative analysis and biomarker identification of the volatile metabolites of different cultivars of Chinese yellowed rice lay a foundation for research on yellowing mechanism.Significance and noveltyThe results of the current study provide a useful basis in the rice yellowing mechanism study. Additionally, a rapid rice aroma analysis method using GC‐IMS was developed. So in the future, yellowed rapid reorganization GC‐IMS technology could be a preferred choice.

Fine mapping and identification of the rice blast-resistance locus Pi-kf2(t) as a new member of the Pi2/Pi9 multigene family

The identification and utilization of broad-spectrum resistance genes is the most effective and economical strategy of controlling rice blast disease. Kangfeng B (KFB), an elite Chinese rice cultivar, has been shown to exhibit broad-spectrum resistance to 53 isolates of Magnaporthe oryzae, the rice blast causative agent, from different regions of China. In this study, we identified a dominant blast-resistance gene at the Pi2/Pi9 locus from cultivar KFB, through genetic analysis and physical mapping. Allele-specific marker-based assessment revealed that Pi2, Pi9, and Piz-t are not the blast-resistance genes in KFB. By combining bulked segregation analysis (BSA) and recessive class analysis (RCA), the blast-resistance gene was fine-mapped to an approximately 249-kb interval between markers InDel-22 and Rm7213 on chromosome 6. Three bacterial artificial chromosome (BAC) clones spanning the region were identified. This region contains 19 predicted genes, including 7 nucleotide binding site–leucine-rich repeat (NBS-LRR) genes at the Pi2/Pi9 locus in japonica cv. Nipponbare genome. Further sequence comparison of the four functional NBS-LRR genes revealed that NBS-LRR2 and NBS-LRR4, as evidenced by their allelic/orthologous to Pi9 or Pi2, had significant differences of 9 to 43 and 14 to 48 amino acids in KFB, respectively, unlike the other known Pi2/Pi9 alleles, suggesting that KFB carries a hitherto undocumented member of the Pi2/Pi9 multigene family. It was tentatively designated as Pi-kf2(t). Our results provide essential information for the isolation of the Pi-kf2(t) gene and will facilitate both map-based cloning and marker-assisted selection of this gene for rice blast-resistance breeding.

Genome-Wide Identification of Insertion and Deletion Markers in Chinese Commercial Rice Cultivars, Based on Next-Generation Sequencing Data

Rice, being a staple food crop for over one-third of the world’s population, has become a potential target for many dishonest traders and stakeholders for mixing with low-grade, low-cost grains/products and poorly nutritious adulterants to make a profit with the least effort. Single-nucleotide and insertion–deletion (InDel) polymorphisms have been widely used as DNA markers, not only in plant breeding but also to identify various traits in rice. Recently, next-generation sequencing (NGS) has produced sequences that allow for genome-wide detection of these molecular markers. These polymorphisms can potentially be used to develop high-accuracy polymerase chain reaction (PCR)-based markers. PCR-based techniques are rapid and successful methods to deal with the problem of adulteration at a commercial level. Here, we report the genome-wide analysis of InDel markers of 17 commercially available Chinese cultivars. In order to achieve accurate results, all samples were sequenced at approximately 30× genome coverage using Illumina HiSeq 2500™ system. An average of 10.6 GB clean reads per sample was produced and ~96.3% of the reads could be mapped to the rice genome reference IRGSP 1.0. After a series of filtering, we selected five InDel markers for PCR validation. The results revealed that these InDel markers can be used for authentication of Korean elite cultivars from the adulterants.

The Role of Node Restriction on Cadmium Accumulation in the Brown Rice of 12 Chinese Rice (Oryza sativa L.) Cultivars.

For selection or breeding of rice (Oryza sativa L.) cultivars with low Cd affinity, the role of node Cd restriction on Cd accumulation in brown rice was studied. A pot experiment was conducted to investigate the concentration of Cd in different sections of 12 Chinese rice cultivars. The results indicated that the Cd accumulation in the brown rice was mainly dependent on the root or shoot Cd concentration. Among the cultivars with nearly equal shoot Cd concentrations, Cd accumulation in brown rice was mainly dependent on the transport of Cd in the shoot. However, the Cd transport in the shoot was significantly restricted by the nodes, especially by the first node. Furthermore, the area of the diffuse vascular bundle in the junctional region of the flag leaf and the first node was a key contributor to the variations in Cd restriction by the nodes.

Marker-assisted breeding of Chinese elite rice cultivar 9311 for disease resistance to rice blast and bacterial blight and tolerance to submergence

Rice (Oryza sativa L.) is the staple food crop for more than half of the world’s population. The development of hybrid rice is a practical approach to increase rice production. However, rice production was frequently affected by biotic and abiotic stresses. Rice blast and bacterial blight are two major diseases in rice growing regions. Rice plantation is also frequently affected by short-term submergence or seasonal floods in wet seasons and drought in dry seasons. The utilization of natural disease resistance (R) genes and stress tolerance genes in rice breeding is the most economic and efficient way to combat or adapt to these biotic and abiotic stresses. Rice cultivar 9311 is widely planted rice variety, either as inbred rice or the paternal line of two-line hybrid rice. Here, we report the pyramiding of rice blast R gene Pi9, bacterial blight R genes Xa21 and Xa27, and submergence tolerance gene Sub1A in 9311 genetic background through backcrossing and marker-assisted selection. The improved rice line, designated as 49311, theoretically possesses 99.2% genetic background of 9311. 49311 and its hybrid rice, GZ63S/49311, conferred disease resistance to rice blast and bacterial blight and showed tolerance to submergence for over 18 days without significant loss of viability. 49311 and its hybrids had similar agronomic traits and grain quality to 9311 and the control hybrid rice, respectively. The development of 49311 provides an improved paternal line for two-line hybrid rice production with disease resistance to rice blast and bacterial blight and tolerance to submergence.

Impact of Elevated Ozone on Nutrient Uptake and Utilization of Chinese Hybrid Indica Rice (Oryza Sativa) Cultivars under Free-Air Ozone Enrichment

ABSTRACTTo assess the effects of ozone (O3) on uptake and utilization of nitrogen, phosphorus, and potassium nutrients in rice for planning rational fertilization under projected O3 elevation. Two hybrid indica cultivars were exposed to ambient and elevated O3 (E-O3) under a free-air O3 enrichment system. E-O3 differently affected the accumulation and distribution of biomass, and the absorption and distribution of nutrients between cultivars. These effects were related to rice cultivar and nutrient type. E-O3 led to significantly decreased partial factor productivity and grain production efficiency (GPE) of nitrogen in both cultivars; however, the effects of E-O3 on GPEs of phosphorus and potassium varied with cultivar. Responses of nutrients harvest indices between cultivars to E-O3 were adverse. Differences between cultivars and elements should be considered when examining E-O3 potentially affecting the nutrient dynamics for the purpose of reducing the amount of fertilizer applied in paddy systems to decrease potential environmental pollution.

The cadmium and lead content of the grain produced by leading Chinese rice cultivars

The cadmium (Cd) and lead (Pb) content in both white and wholemeal flour milled from 110 leading rice cultivars was assessed. The white flour Cd content ranged from <0.0025 to 0.2530mg/kg (geometric mean (GM)=0.0150mg/kg), while its Pb content ranged from <0.0250 to 0.3830mg/kg (GM=0.0210mg/kg). The indica types took up higher amounts of Cd and Pb than did the japonica types. Although the heavy metal content of wholemeal flour tended to higher than that of white flour, nevertheless 84.5% (Cd) and 95.4% (Pb) of the entries were compliant with the national maximum allowable concentration of 0.2000mg/kg of each contaminant. An analysis of the Cd content in the white flour of three indica type cultivars grown in two consecutive years at two locations indicated that Cd content may be significantly affected by the conditions prevailing in the growing season.

Allele-specific marker-based assessment revealed that the rice blast resistance genes Pi2 and Pi9 have not been widely deployed in Chinese indica rice cultivars.

BackgroundThe most sustainable approach to control rice blast disease is to develop durably resistant cultivars. In molecular breeding for rice blast resistance, markers developed based on polymorphisms between functional and non-functional alleles of resistance genes, can provide precise and accurate selection of resistant genotypes without the need for difficult, laborious and time-consuming phenotyping. The Pi2 and Pi9 genes confer broad-spectrum resistance against diverse blast isolates. Development of allele-specific markers for Pi2 and Pi9 would facilitate breeding of blast resistant rice by using the two blast resistance genes.ResultIn this work, we developed two new markers, named Pi9-Pro and Pi2-LRR respectively, targeting the unique polymorphisms of the resistant and susceptible alleles of Pi2 and of Pi9. The InDel marker Pi9-Pro differentiates three different genotypes corresponding to the Pi2/Piz-t, Pi9 and non-Pi2/Piz-t/Pi9 alleles, and the CAPS marker Pi2-LRR differentiates the Pi2 allele from the non-Pi2 allele. Based on the two newly developed markers and two available markers Pi2SNP and Pi9SNP, the presence of Pi2 and Pi9 was assessed in a set of 434 rice accessions consisting of 377 Chinese indica cultivars/breeding materials and 57 Chinese japonica cultivars/breeding materials. Of the 434 accessions tested, while one indica restorer line Huazhan was identified harboring the Pi2 resistance allele, no other rice line was identified harboring the Pi2 or Pi9 resistance alleles.ConclusionsAllele-specific marker-based assessment revealed that Pi2 and Pi9 have not been widely incorporated into diverse Chinese indica rice cultivars. Thus, the two blast resistance genes can be new gene sources for developing blast resistant rice, especially indica rice, in China. The two newly developed markers should be highly useful for using Pi2 and Pi9 in marker-assisted selection (MAS) breeding programs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-016-0091-8) contains supplementary material, which is available to authorized users.

Transformation of upland rice with the bar gene and selection for resistance to the herbicide Basta

In this study, Chinese upland rice cultivars including Handao297 and Handao502 were transformed with the anti-herbicide bar gene in order to achieve efficient weed control. PCR amplification, Southern blot analysis and field Basta resistance identification in early T0, T1, and late generation T6 and T11–T13 illustrated that the exogenous bar gene had been integrated into the genome of the upland rice varieties with stable expression in successive generations. Different transformants had a different gene copy numbers, which was not related to Basta resistance. Some of the transgenic lines showed gene silencing, whereas multiple copies of the bar gene were observed in other late generation transgenic lines. Basta resistance can thus be inherited stably among generations, and an optimal Basta concentration and selective pressure are suitable for resistance segregation and breeding of homozygous progenies with high resistance. After three generations of successive Basta resistance selection in 207 T0 plants, we obtained 555 T3 lines. Comprehensive identification and selection for Basta resistance, drought resistance, yield, and other agronomic traits in nine generations yielded two promising transgenic lines, HD297T-31 and HD297T-523. Although both varieties were resistant to 0.1 % Basta, HD297T-31 possessed high (100 %) resistance to Basta while HD297T-523 showed moderate (95 %) resistance. Moreover, during the reproductive stage, the stems, sheaths, leaves, and panicles of HD297T-31 were immune-highly resistant to highly-moderately resistant to 0.5 % Basta, whereas, they were highly resistant–moderately resistant to 1 % Basta. HD297T-523 was immune-highly resistant and immune-highly resistant to 0.5 and 1 % Basta respectively. The plant and stem percentage sensitive to 0.5 % Basta was lower than 1 and 3 % respectively. Since HD297T-31 showed isozygosity, it could be used as a new variety in production.

Variations between the photosynthetic properties of elite and landrace Chinese rice cultivars revealed by simultaneous measurements of 820 nm transmission signal and chlorophyll a fluorescence induction

The difference between the photosynthetic properties of elite and landrace Chinese rice cultivars was studied, using chlorophyll a fluorescence induction (mostly a monitor of Photosystem II activity) and I820 transmission signal (mostly a monitor of Photosystem I activity) to identify potential photosynthetic features differentiating these two groups, which show different degrees of artificial selection and grain yields. A higher fluorescence (related to PSII) IP rise phase and a lower P700+ (related to PSI) accumulation were observed in the elite cultivars as compared to the landraces. Using these data, together with simulation data from a kinetic model of fluorescence induction, we show that the high IP rise phase and the low P700+ accumulation can be a result of transient block on electron transfer and traffic jam on the electron acceptor side of PSI under a high [NADPH]/[NADP+] ratio. Considering that the ferredoxin NADP+ reductase (FNR) transcript levels of XS134 (a representative elite cultivars) remains unaffected during the first few minutes of light/dark transition compared to Q4145 (a representative landrace cultivars), which shows a strong decline during the same time range, we propose that the FNR of elite cultivars may take more time to be inactivated in darkness. During this time the FNR enzyme can continue to reduce NADP+ molecules, leading to initially high [NADPH]/[NADP+] ratio during OJIP transient. These data suggested a potential artificial selection of FNR during the breeding process of these examined elite rice cultivars.

Rice Bran Affects Dry-matter Production of Chinese and Japanese Rice Cultivars

The effect of rice bran on dry matter production of different rice cultivars, namely the Chinese panicle weight types and Japanese panicle number types, was evaluated in field conditions, with growth, canopy production structure and the root system determined over a period of 60 days. The treatments consisted of rice cultivars with 1000 kg ha1 rice bran without agrochemicals (RB), cultivars with chemical fertilizer and cultivars with herbicide, with the latter serving as a control. The crop growth rate (CGR) and mean leaf area index (mLAI) in RB treatment were lower than that of the control; however, the net assimilation rate (NAR) was higher for all growth stages in this treatment. It was noted that CGR in RB and the control treatment depended greatly on mLAI during the early and middle growth stages, whereas CGR was more dependent on NAR in the late growth stage. Correlation between CGR in middle stage and the extinction coefficient of the canopy (k) at heading was apparent (p < 0.05). NAR in middle stage was positively correlated with mean leaf color and specific leaf weight (SLW). The correlations between NAR in the late stage and bleeding rate per number of primary roots, and per leaf area at maturity was apparent (p < 0.01). Root vitality and NAR were higher in RB treatment. The photosynthesis-related traits after heading in RB treatment were better than the control. Reduction of ∆W in RB treatment as well as the spikelets number (SN) was unapparent. The panicle number type cultivars did not inhibit growth during the early and middle growth stages with the presence of rice bran. The difference between growth, panicle number and weight cultivars was insignificant in the late stage. Discipline: Crop production Additional key words: bleeding rate, growth analysis, light extinction coefficient, the panicle number type cultivars, root system. This research was supported in part by Tianjin natural science fund for Scientific Research (No.11JCYBJC27100) from the Tianjin Municipal Science and Technology Commission, China. The Project Sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry (No.46). This research was supported in part by the ScienceT accepted 2 March 2015 Introduction The use of nitrogen in paddy cultivation in China is three times higher than in Japan. In this context, excess application of chemical fertilizer in paddy cultivation pollutes the environment and has adverse effects on both aquatic and terrestrial organisms. The use of chemical fertilizers increases operation costs, resulting in higher rice and rice product prices. It is, therefore, important to find new alternatives as substitutes for chemical fertilizer in paddy farming to alleviate environmental issues arising from their use. Rice bran is often used in the organic paddy farming in Japan because of its efficacy as a fertilizer and herbicide. This cultivation technique fulfills the growing demand for agriculture products with fewer or no agrochemicals to

Development and Application of a Functional Marker of the Blast Resistance Gene Pi35 in Rice

Rice blast is one of the most destructive diseases, and breeding resistant cultivars is considered to be the most eco- nomical and effective strategy to control this disease. The Pi35 gene shows partial resistance to leaf blast and has been used as a broad-spectrum and durable resistance source in rice breeding programs in Japan. However, its distribution is not clear in Chinese rice germplasm and cultivars. For the purpose to facilitate the application of Pi35 in rice breeding programs in China, we com- pared the coding sequences of Pi35 alleles in multiple resistant and susceptible rice cultivars, found a specific nucleotide 3780T which was only present in the functional resistance allele of Pi35, and further developed a Pi35 functional marker (Pi35-dCAPS). Among 281 rice accessions including 10 Fukei 138-derived japonica cultivars, 67 leading cultivars, and 204 accessions of rice mini-core collection of Chinese germplasm, five Fukei 138-derived cultivars (Kenjiandao 3, Kenjiandao 6, Kendao 8, Suijing 3, and Longjing 34) and two mini-core accessions (japonica cv. Funingzipijingzi and indica cv. Ximaxian) were detected to possess the intact Pi35 gene by using the Pi35-dCAPS marker in combination with the genomic sequencing of Pi35. These results will greatly facilitate the utilization of Pi35 in rice breeding programs by marker-assisted selection.

Effect of Slow Release Fertilizer on Nitrogen Use Efficiency for Grain Yield in Chinese High-Yielding Rice Cultivars

Effect of Slow Release Fertilizer on Nitrogen Use Efficiency for Grain Yield in Chinese High-Yielding Rice Cultivars

Effect of Slow Release Fertilizer on Nitrogen Absorption and Fertilizer Nitrogen Recovery Rate in Chinese High-Yielding Rice Cultivars

中国における水稲の多収穫多施肥栽培において施肥窒素（N）吸収率の向上を目的とし，多収性水稲品種のN吸収に及ぼす緩効性肥料の施用効果を調査した．緩効性肥料の施用は，中国産多収性品種の揚稲4号（YD）および武育粳3号（WY）において幼穂形成期までの肥料由来N吸収量を有意に増加させた．この結果，施肥N吸収率が有意に増加し，YDでは成熟期N含有量の有意な増加も認められた．YDは幼穂形成期から出穂期にかけてのN吸収量が高かったが，WYはより早い時期のN吸収量が高く，YDに対してはWYより肥効の長い緩効性肥料の施用が有効であると推察される．YDの施肥N吸収率は，シグモイド型緩効性肥料（S区）＞リニア型緩効性肥料（L区）＞塩安の分施（C区）の傾向があり，施肥N量の増加に伴いC区では有意に増加したが，S区およびL区では有意な変化は認められなかった．以上のことから，YDへの緩効性肥料，特にシグモイド型肥料の施用は施肥N吸収率が高いこと，それにより施用量の削減が可能であることから，環境負荷の軽減に有効であると考えられた．

Study on the granular characteristics of starches separated from Chinese rice cultivars

Granule size distribution, the relative crystallinity, morphology and thermal degradation of starches from 10 different non-waxy rice cultivars were measured in present study. The relationships between granular structure and thermogravimetric parameters of tested starches were evaluated using Pearson correlation analysis. The range of median size for rice starches was 6.23–7.81 μm. The relative crystallinity of 10 non-waxy rice starches ranged from 20.4% to 33.4%. The range of activation energy from different rice starches was between 155.6 and 201.5 kJ/mol. The Pearson correlation results showed that the relative crystallinity was positively correlated (r = 0.6750, p < 0.05) with the percentage of branch chains with DP12–23. Furthermore, the activation energy of the rice starches showed a positive correlation (r = 0.7903, p < 0.01) with relative crystallinity.

An efficient regeneration system and Agrobacterium-mediated transformation of Chinese upland rice cultivar Handao297

A highly efficient tissue culture system and Agrobacterium-mediated transformation protocol for Chinese upland rice cultivar Handao297 has been established with mature embryos as explants. Up to 81.2% of mature embryos were induced to regenerate good-quality calli on NB medium (a medium combining N6 macronutrient components and B5 micronutrient and organic components) containing 3 mg/l 2,4-dichlorophenoxyacetic acid in 10 days. More than 80% of the calli were morphogenic within 1 week and regenerated green plantlets within 1 month on Murashige and Skoog medium supplemented with 0.5 mg/l 6-benzyladenine, 0.5 mg/l kinetin, 1 mg/l zeatin, 0.5 mg/l thidizazuron (TDZ), 0.5 mg/l naphthaleneacetic acid, 0.15 mg/l indoleacetic acid, and 0.15 mg/l indolebutyric acid. This tissue culture system was suitable for Agrobacterium-mediated transformation of upland rice Handao297. Furthermore, some important factors affecting transformation frequency were investigated with Agrobacterium strain AGL1 containing the plasmid pCAMBIA1381. The addition of 30 mg/l hygromycin B followed by 60 mg/l hygromycin B to the selection induction medium facilitated the revival of calli from selection and reduced false positive calli. Hygromycin B at 10 mg/l was most effective in suppressing non-transgenic callus growth in the differentiation medium. The addition of TDZ to the differentiation medium promoted the morphogenesis of calli and facilitated the generation of adventitious shoots by five to tenfold in comparison to medium without TDZ.