Rice Variety IR64 Research Articles

Mapping and characterization of a quantitative trait locus resistance to the brown planthopper in the rice variety IR64

BackgroundRice planthoppers (main brown planthopper, Nilaparvata lugens Stål; BPH) was one of substantial threats to Asia rice production as its serious destruction and difficulties in control under field conditions. Notably, host-plant resistance was proved to be one of the effective ways to manage the pest. And stronger virulence will probably emergence when continuous use of insecticides. Therefore, more resistance genes with different resistance mechanisms were needed to be detected and then applied in the rice breeding practice.ResultsResistance genes in the rice variety IR64 were evaluated considering the seedling bulk test and seedling survival rate. As a result, a locus with a large LOD score of 7.23 was found between markers RM302 and YM35 on chromosome 1. The locus explained 36.9% of phenotypic variation and was tentatively denominated Bph37. Moreover, Bph1 was detected to be harbored by the markers RM28366 and RM463, and had the largest LOD score of 2.08, explaining 7.7% of phenotypic variance in the same mapping population. Finally, the preliminary-near-isogenic-lines (pre-NILs) carrying Bph37 exhibited significant tolerance to the insects. But no antibiotic or antixenotic effects were observed in the resistant plants when infested with the insects.ConclusionsWe mapped one major BPH resistance gene Bph37 in consideration of seedling survival rate and the resistance lines showed tolerance to BPH. The detected gene should be beneficial for understanding the resistance mechanism of rice to BPH and for insect-resistance rice breeding programs.

Varietal differences in the effect of rice ageing on starch digestion

The purpose of this study was to provide, for the first time, a comprehensive account of the potential effects of storage (37 °C) on physicochemical properties and digestion behaviour of three highly consumed Iranian rice varieties (Hashemi, Domsiyah and Gohar). After ageing, the content of thiol groups was significantly reduced only in the case of Hashemi. The ageing process did not significantly change the rate and extent of starch digestion in Gohar and Domsiyah, but a clear reduction was observed in Hashemi. The results suggested that the changes in peptide subunit composition contribute to the potential efficiency of ageing for controlling rice digestion behaviour. This study suggests that varietal differences may play a major role in the effectiveness of ageing in modifying rice physicochemical properties and starch digestion dynamics. The results also indicated that starch digestibility didn't follow amylose content level and suggests the importance of other components on rice digestibility.

Effect of Plant Spacing on Growth and Yield of Rice (Oryza sativa L.) under Submerged Condition

The experiment was conducted to find out the effect of plant spacing on the performance of rice variety IR-64 and IR64-Sub1 under conventional and Submerged condition at the National Rice Research Institute (NRRI), Cuttack, Odisha during the Rabi season of 2018. Different planting densities were maintained using different spacing's. These include (S1) 15 cm × 10 cm, (S2) 15 cm × 20 cm. The experiment was laid out in a randomized complete block design with 3 replications spacing of 15 cm × 10 cm with produced the highest grain yield of 350 gm-2 in submerged condition on IR64-Sub1 rice cultivar, which was significantly higher than the yield with recommended density (15 cm × 10 cm with IR64 Sub1). This yield was increased due to higher number of panicles m-2. This result suggests that higher planting density (15 cm×10 cm) rather than increased number of seedling hill-1 is necessary for getting higher yield of IR-64Sub1 rice cultivar in continuous submerged condition (where V1=IR 64, V2=IR-64 Sub1, S1=15 cm×10 cm, S2=20 cm×15 cm).

Marker-free transgenic rice plant overexpressing pea LecRLK imparts salinity tolerance by inhibiting sodium accumulation.

PsLecRLK overexpression in rice provides tolerance against salinity stress and cause upregulation of SOS1 pathway genes, which are responsible for extrusion of excess Na+ ion under stress condition. Soil salinity is one of the most devastating factors threatening cultivable land. Rice is a major staple crop and immensely affected by soil salinity. The small genome size of rice relative to wheat and barley, together with its salt sensitivity, makes it an ideal candidate for studies on salt stress response caused by a particular gene. Under stress conditions crosstalk between organelles and cell to cell response is imperative. LecRLK is an important family, which plays a key role under stress conditions and regulates the physiology of the plant. Here we have functionally validated the PsLecRLK gene in rice for salinity stress tolerance and hypothesized the model for its working. Salt stress sensitive rice variety IR64 was used for developing marker-free transgenic with modified binary vector pCAMBIA1300 overexpressing PsLecRLK gene. Comparison of transgenic and wild-type (WT) plants showed better physiological and biochemical results in transgenic lines with a low level of ROS, MDA and ion accumulation and a higher level of proline, relative water content, root/shoot ration, enzymatic activities of ROS scavengers and upregulation of stress-responsive genes. Based on the relative expression of stress-responsive genes and ionic content, the working model highlights the role of PsLecRLK in the extrusion of Na+ ion from the cell. This extrusion of Na+ ion is facilitated by higher expression of SOS1 (Na+/K+ channel) in transgenic plants as compared to WT plants. Altered expression of stress-responsive genes and change in biochemical and physiological properties of the cell suggests an extensive reprogramming of the stress-responsive metabolic pathways by PsLecRLK under stress condition, which could be responsible for the salt tolerance capability.

Effectiveness and efficiency of potassium fertilizer application to increase the production and quality of rice in entisols

The study aimed to determine the appropriate dose of K-type fertilizer on the production and quality of IR-64 rice varieties in Entisols. The study was conducted on Entisols, Nglarang, Basin, Kebonarum, Klaten, Central Java, Indonesia. Randomized Complete Block Design (RCBD) was used with 2 factors and three replicates. Factor I: types of K fertilizer: KCl, ZK, and KNO3. Factor II: K fertilizer dose consists of four levels: 0, 50, 100 and 150 kg K2O ha-1. The results showed that the type of K fertilizer KCl, ZK, and KNO3 gave similar effect on growth and yield of rice variety IR 64 on Entisols. Dose of K fertilizer increased the growth and yield of rice but an increased dose provides improved meaningful results. K fertilizer with a dose of 50 kg ha-1 K2O is the most efficient, with the agronomic efficiency for dry grain highest yield of 13.6 kg/kg K2O achieved by ZK fertilizer.

PRODUKTIVITAS PADI SAWAH PADA KEPADATAN POPULASI BERBEDA

[THE PRODUCTIVITY OF LOWLAND RICE UNDER DIFFERENT POPULATION DENSITIES]. Population density will determine the crop productivity on either individual plant basis or area basis. Objective of this study was to evaluate the productivity of lowland rice at different population densities. Rice variety IR-64 was planted on 13.2 m x 10 m plot at four population densities (16, 25, 49 and 100 plant m-2) in a completely randomized design with three replications. Observations were made on the yield components on individual plant basis and grain yield per area. Results indicated that tiller number, number of productive tiller, number of spikelet per panicle, number of fertile spikelet, and grain yield per hill were reduced as the population density was increased. On contrary, grain yield per 100 m2 was increased linearly in accordance to the increment of population density, where 47.57 kg grain per 100 m2 produced at the density of 16 plant m-2 and 86.53 kg was produced at the density of 100 plant m-2.

Variability of upland rice genotypes response to low light intensity

Hairmansis A, Yullianida, Supartopo, Jamil A, Suwarno. 2017. Variability of upland rice genotypes response to low light intensity. Biodiversitas 18: 1122-1129. Plantation areas have a great potential to be utilized for upland rice production through intercropping. One of major constraints in the cultivation of upland rice as intercropping is low light intensity caused by shading. Improvement of rice varieties for shading tolerance is therefore important to increase rice production in upland areas. The objective of this study was to investigate the variability of upland rice genotypes responses to shading and identify the best genotypes for intercropping rice cultivation. Thirty-eight upland rice breeding lines, the shading tolerant rice variety Jatiluhur, and the shading susceptible rice variety IR64 were evaluated for their response to low light intensity in the greenhouse and the field. Greenhouse screening was conducted to determine their shading tolerance in vegetative stage while evaluation in the field was performed to evaluate their agronomic performance under 55% shading and normal conditions. Variation in upland rice genotypes on low light stress was revealed both in greenhouse and field trials. In the greenhouse trial, 12 genotypes showed higher survival rate compared to tolerant rice variety Jatiluhur. Field evaluation demonstrated that 55% shading increased plant height, reduced productive tiller number, delayed flowering time, increased spikelet sterility and reduced grain yield. Upland rice breeding line B11908F-TB-3-WN-1 showed high yield relative in shading condition compared to normal condition and had high-stress tolerance index (STI) which indicated the genotype was tolerant to shading.

IMPACT OF INSECT PEST ON YIELD OF RICE: CASE OF VARIETIES IR 46 AND NERICA 3 IN AGROECOSYSTEME OF MAGA FAR NORTH OF CAMEROON

This present study which is base on the effect of pest insects on the production of rice was done in the Far North Cameroon in the irrigated rice ecosystem of Maga. On one part, it consisted of the determination of the biological diversity of pest insects of rice in the rice ecosystem of Maga, to evaluate the damages and the dynamism of pest insects on the phenologic stage of rice and on the other part and to evaluate the effect of insecticide lynx on the pest insects and the production of rice. A split plot disposition of two rice varieties (irrigated rice variety IR 46 and the rainy season rice variety NERICA 3) and two treatments (control and chemical treatment) were adopted. The insects were captured with the help of a sweep net on every portions on the phenologic stages of rice, from the 15th day after planting to harvesting. This method of collecting insects consists of sweeping insects, on the portions or 50 sweeps per portion. These collections of pest insects on the two rice varieties have permited us to see the dynamism of pest insects on the different phenological stages of rice, and a knowledge on their abundance. The results obtained on the biological diversity have shown that 2465 pest insects of rice were collected on the IR 46 variety and 3264 on the NERICA 3 variety. Concerning the dynamism of the pest insects, we have observed a variation of the number of pest insects following the different phenological stages of rice. Concerning the damages due to the pest insects, lose due to these pest insects was evaluated at 49.98% total, 26.30% lose at the talling stage and 23.68% at the harvest on the two varieties. The chemical insecticide lynx have reduced the pest at a rate of 12.585% in the nursery, 20.4725% at the talling stage, 9.305% at the ear and 8.7325% at maturity. The output was obtained at 2.13 t/ha for the IR 46 variety and 1.91 t/ha for the NERICA 3 variety. This result permits us to say that many pest insects occupies the irrigated rice ecosystem of Maga, they are dynamic and leads to the damages on the rice production. The insecticide lynx used permit the reduction of the pest insects and hence increasers production.

A Multidisciplinary Phenotyping and Genotyping Analysis of a Mapping Population Enables Quality to Be Combined with Yield in Rice.

In this study a mapping population (F8) of ca 200 progeny from a cross between the commercial rice varieties Apo and IR64 has been both genotyped and phenotyped. A genotyping-by-sequencing approach was first used to identify 2,681 polymorphic SNP markers which gave dense coverage of the genome with a good distribution across all 12 chromosomes. The coefficient of parentage was also low, at 0.13, confirming that the parents are genetically distant from each other. The progeny, together with both parents, were grown under irrigated and water restricted conditions in a randomised block design. All grain was harvested to determine variation in yield across the population. The grains were then polished following standard procedures prior to performing the phenotyping analyses. A Gas Chromatography—Mass Spectrometry approach was used to determine the volatile biochemical profiles of each line and after data curation and processing, discriminatory metabolites were putatively identified based on in-house and commercial spectral libraries. These data were used to predict the potential role of these metabolites in determining differences in aroma between genotypes. A number of QTLs for yield and for individual metabolites have been identified. Following these combined multi-disciplinary analyses, it proved possible to identify a number of lines which appeared to combine the favourable aroma attributes of IR64 with the favourable (higher) yield potential of Apo. As such, these lines are excellent candidates to assess further as potential genotypes to work up into a new variety of rice which has both good yield and good quality, thus meeting the needs of both farmer and consumer alike.

Identification and Classification of Three Iranian Rice Varieties in Mixed Bulks Using Image Processing and MLP Neural Network

Abstract Due to variation in economic value of different varieties of rice, reports indicating the possibility of mixing different varieties on the market. Applying machine vision techniques to classify rice varieties is a method which can increase the accuracy of classification process in real applications. In this study, several morphological and textural features of rice seeds’ images were examined to evaluate their efficacy in identification of three Iranian rice varieties (Tarom, Fajr, Shiroodi) in their mixed samples. On the whole, 666 images of rice seeds (222 images of each variety) were acquired at a stable illumination condition and totally, 17 morphological and 41 textural features were extracted from seeds images. Principal component analysis (PCA) method was employed to select and rank the most significant features for the classification. Subsequently, the MLP neural network classifier was employed for classification of rice varieties in the mixed bulks of three and two varieties, using top selected features. The network was three-layered feed forward type and trained using two training algorithms (BB and BDLRF). The classification accuracy of 55.93, 84.62 and 82.86 % for Fajr, Tarom and Shiroodi, 86.96 and 93.02 % for Fajr and Shiroodi, 86.84 and 96.08 % for Tarom and Shiroodi and 91.49 and 95.24 % for Fajr and Tarom were obtained in test phase, respectively.

THE EFFECT OF HEATING ON PHYSICOCHEMICAL CHARACTERISTICS OF RICE BRAND OIL

Rice bran oil has a potential in lowering blood cholesterol. The oil content extracted from rice bran isa influenced by several factors such as raw material and processing method. This research was conducted to study the effect of heating on the physicochemical characteristics of rice bran oil. The study was carried out at the Food Technology and Nutrition Laboratory and Biotechnological Science Laboratory of the Inter University Center, Bogor Agricultural University, from February to MAy 1997. Bran used was from IR64 rice variety obtained from a local milling rice in Tambak Dahan, Binong-Subang, West Java. Rice bran was subjected to different period of heating (0, 15 and 30 minutes) at 121<sup>o</sup>C by using an autoclave, then the oil was extraxted by using hexane solvent followed by standard processing at room temperature (28-30<sup>o</sup>C) and 40<sup>o</sup>C for two hours. The parameters observed were oil content and its quality such as saponification, iodine, acid, peroxide, tiobarbituric acid, and triglyceric acid values as well as oil color. The results showed that oil extracted from rice bran was high, ranging from 9.65 to 11.02%. Heating (sterilizing) of the rice bran for 15 and 30 minutes at 120<sup>o</sup>C proir to extraction increased the oil content. The Quality of rice bran oil extracted met the standard of AOAC.

THE EFFECT OF HEATING ON PHYSICOCHEMICAL CHARACTERISTICS OF RICE BRAND OIL

Rice bran oil has a potential in lowering blood cholesterol. The oil content extracted from rice bran isa influenced by several factors such as raw material and processing method. This research was conducted to study the effect of heating on the physicochemical characteristics of rice bran oil. The study was carried out at the Food Technology and Nutrition Laboratory and Biotechnological Science Laboratory of the Inter University Center, Bogor Agricultural University, from February to MAy 1997. Bran used was from IR64 rice variety obtained from a local milling rice in Tambak Dahan, Binong-Subang, West Java. Rice bran was subjected to different period of heating (0, 15 and 30 minutes) at 121<sup>o</sup>C by using an autoclave, then the oil was extraxted by using hexane solvent followed by standard processing at room temperature (28-30<sup>o</sup>C) and 40<sup>o</sup>C for two hours. The parameters observed were oil content and its quality such as saponification, iodine, acid, peroxide, tiobarbituric acid, and triglyceric acid values as well as oil color. The results showed that oil extracted from rice bran was high, ranging from 9.65 to 11.02%. Heating (sterilizing) of the rice bran for 15 and 30 minutes at 120<sup>o</sup>C proir to extraction increased the oil content. The Quality of rice bran oil extracted met the standard of AOAC.

Pengaruh Hormon Asam Indol Asetat yang Dihasilkan Azospirillum sp. terhadap Perkembangan Akar Padi

<p>Free-living bacteria of the<br />genus Azospirillum live in close association with rice roots.<br />This bacteria produced indole acetic acid (IAA), a plant<br />growth hormon, to the environment. IAA was isolated from<br />cultures of Azospirillum strains and investigated for its effect<br />on root development and plant height of rice variety IR64 in<br />vitro. Rice cultures of variety IR64 were grown in vitro and<br />inoculated with cultures of Azospirilllum. Production of IAA<br />by the bacterium during its growth period in rice culture medium<br />containing different levels of nitrogen was observed.<br />Results of the experiment showed that strains Azospirillum<br />Az15 and Az44 had a high ability to produce IAA, i.e., 57.93<br />μg/ml at 12 days after incubation (DAI) and 40.42 μg/ml at 7<br />DAI, respectively. The IAA production pattern of Azospirillum<br />Az15 and Az44 in the liquid medium were fluctuative<br />until the end of the incubation period, while that of the strain<br />Az7 was linier. Strain Az7 gave a better effect on the root<br />development and plant height than strains Az15 and Az44.<br />Treatment combination of strain Az7 and 100% nitrogen gave<br />highest root development. High level of nitrogen increased<br />IAA content in the uninoculated culture, while low IAA<br />content on the inoculated one. Inoculation the culture with<br />strain Az7 together with 50% nitrogen application resulted in<br />the IAA content, root dry weight, root length, fiber root number,<br />and plant height as high as those on cultures containing<br />100% nitrogen (1 mM NH4NO3) without inoculation. Inoculation<br />of rice culture with Azospirillum is expected to reduce<br />nitrogen application on rice IR64 by the IAA production as<br />indicated by significant changes in the root growth and<br />development. A higher concentrations of IAA tend to give<br />better effects on the root growth and development of rice<br />IR64.</p>

Association analysis, genetic diversity and haplotyping of rice plants under salt stress using SSR markers linked to SalTol and morpho-physiological characteristics

Knowledge of genetic diversity could aid in providing useful information in the selection of material for breeding such as hybridization programs and quantitative trait loci mapping. The present study was conducted to evaluate salinity tolerance of Iranian rice varieties. This research was carried out in three separate experiments (control, 6 and 12 dS m−1 NaCl) each based on completely randomized design with 44 rice varieties and three replications. Fourteen days after salt treatments, root and shoot fresh and dry weight, Na+ and K+ concentration, Na+/K+ ratio, root and shoot length, biomass gain, total fresh weight, root/shoot length ratio and shoot/root weight ratio were measured. The varieties were also genotyped for 12 closely linked microsatellite markers to SalTol. Haplotype and association analysis was conducted using these SSR markers for identification of loci related to salt tolerance. The tolerance scores under salinity stress showed that the varieties FL478, Hassani, Gharib, Shahpasand, Nemat, Domzard, Ghasroddashti, Ahlamitarom, Hassansaraee and Binam with more biomass, root and shoot lengths, and low Na+/K+ ratio were tolerant to salinity stress. Association analysis was indicated that there are some informative markers on chromosome 1 in the local and improved Iranian rice varieties genetic background including RM8094, RM1287, AP3206 and RM3412 explaining considerable percentage of the salt tolerance-related traits. These informative markers can be used in future breeding programs such as marker-assisted selection.

Respons Biologi Wereng Batang Coklat terhadap Biokimia Tanaman Padi

In developing rice varieties resistant to brown planthopper (BPH), information on responses of the BPH to the rice plants were needed. The aim of the research was to study the biological responses of BPH on biochemical factors of some rice varieties. The study was conducted on June 2010 to April 2012 in Muara Research Station, of the Indonesian Center for Rice Research (ICRR) and at Laboratory of Physiology and Toxicology, Plant Protection Department, Bogor Agriculture University. The biological responses of the BPH to rice varieties were studied in terms of adult settling preference, feeding activity using the honeydew test, and life table analysis. The biochemical factors of the rice varieties, namely sucrose and oxalic acid contents were analyzed. Rice varieties TN1 (no resistance gene), IR26 (Bph1), IR42 (bph2), IR64 (Bph1+), IR74 (Bph3), PTB33 (bph2+Bph3), and Inpari13 (unknown resistance gene) were used in this study. The BPH showed similar non-preference reactions to the resistant varieties and Inpari13 for settling. Feeding activity of the adult female BPH was the highest on the susceptible variety TN1 and the lowest on the resistant variety PTB33. The highest mortality of BPH occurred at larval stages, especially in the first and second instars. The intrinsic rate of increase (rm) and net reproductive rate (Ro) of the BPH were higher on the susceptible variety TN1, but the doubling time (DT) was shorter than those on the resistant varieties. The resistant variety PTB33 contained high oxalic acid and low sucrose. On the contrary, the susceptible variety TN1 contained low oxalic acid and high sucrose. These biochemical factors contributed in rice plant resistance to BPH.

Analysis of flavor volatiles of some Iranian rice cultivars by optimized static headspace gas chromatography–mass spectrometry

Static headspace coupled to gas chromatography–mass spectrometry (SHS-GC–MS) was applied to the extraction and analysis of volatiles in some Iranian rice varieties. Optimization of static headspace sampling was investigated by full factorial design and a face-centered central composite design procedure. According to the results of full factorial design, the effective parameters of static headspace sampling were extraction temperature (T) and extraction time (t). Then a central composite design was applied to find the optimum level of these factors. The results of three replications of experiments under optimal conditions (T = 100 °C, t = 900 s) indicated that, there is a good agreement between the predicted (5.28) and experimental (5.20) responses (98.48 %). Then developed method was used for analysis of volatile chemicals in three Iranian rice cultivars. According to the results of GC–MS analysis 26, 21, and 19 chemicals were assigned to Domsiah, Deylamani, and Tarom rice samples, respectively. The major compounds identified in these samples were the alkyl aldehydes. The results obtained are promising for future isolation and identification of the flavor volatiles of other rice cultivars by SHS-GC–MS analysis. The method of static headspace GC–MS has been developed and has proven to provide an effective means for simple and rapid quantitative analysis of the aroma compound of rice. A central composite design was applied to found the optimal conditions. The results of three replications of experiments under optimal conditions (T = 100 °C, t = 900 s) indicated that, there is a good agreement between the predicted (5.28) and experimental (5.20) responses (98.48 %). Then, developed method was used to analyze the volatile chemicals in the rice samples. A total of 26, 21, and 19 chemicals were assigned to Domsiah, Deylamani, and Tarom rice samples, respectively.

Differential Responses of Two Rice Varieties to Perchlorate Stress

Two rice varieties, one perchlorate-tolerant (Gannuoxiang, GN) and the other perchlorate-sensitive (IR65598-112-2, IR), were exposed to 20, 200, and 400 mg/kg soil perchlorate to investigate their physiological responses and perchlorate accumulation. It was found that perchlorate decreased leaf chlorophyll content in both rice varieties. The activities of superoxide dismutase (SOD) and catalase (CAT) decreased while peroxidase (POD) increased in both rice varieties under perchlorate stress at tillering stage. Rice variety IR showed earlier physiological response and was more affected by perchlorate than GN. Perchlorate induced physiological response in different ways depending on perchlorate contamination level, rice variety, and growing stage. Perchlorate concentration in leaves was significantly higher than that in roots, stems and seeds. Perchlorate accumulation in IR leaves was higher than GN, but GN stored more perchlorate in its edible portion at low perchlorate level. These results indicated that high sensitivity of the rice variety IR to perchlorate stress might be due to antioxidant enzymes in perchlorate-detoxification and its higher perchlorate accumulation in leaves.

Breeding high-yielding drought-tolerant rice: genetic variations and conventional and molecular approaches.

The increased occurrence and severity of drought stress have led to a high yield decline in rice in recent years in drought-affected areas. Drought research at the International Rice Research Institute (IRRI) over the past decade has concentrated on direct selection for grain yield under drought. This approach has led to the successful development and release of 17 high-yielding drought-tolerant rice varieties in South Asia, Southeast Asia, and Africa. In addition to this, 14 quantitative trait loci (QTLs) showing a large effect against high-yielding drought-susceptible popular varieties were identified using grain yield as a selection criterion. Six of these (qDTY 1.1 , qDTY 2.2 , qDTY 3.1 , qDTY 3.2 , qDTY 6.1 , and qDTY 12.1 ) showed an effect against two or more high-yielding genetic backgrounds in both the lowland and upland ecosystem, indicating their usefulness in increasing the grain yield of rice under drought. The yield of popular rice varieties IR64 and Vandana has been successfully improved through a well-planned marker-assisted backcross breeding approach, and QTL introgression in several other popular varieties is in progress. The identification of large-effect QTLs for grain yield under drought and the higher yield increase under drought obtained through the use of these QTLs (which has not been reported in other cereals) indicate that rice, because of its continuous cultivation in two diverse ecosystems (upland, drought tolerant, and lowland, drought susceptible), has benefited from the existence of larger genetic variability than in other cereals. This can be successfully exploited using marker-assisted breeding.

OsHox4 regulates GA signaling by interacting with DELLA-like genes and GA oxidase genes in rice

Gibberellic acid (GA) plays an essential role in many plant growth and developmental processes. Overexpression of rice (Oryza sativa L.) HOMEOBOX4 (OsHox4) gene in rice variety IR64 under the control of CaMV 35s promoter caused varying degrees of dwarfism and bushy tillers. Further investigation showed that over-expression of OsHox4 in indica rice induced semi-dwarf by repressing stems cell elongation. This repression could be eliminated by exogenously applied Gibberellin-4 (GA4) suggested that OsHox4 was involved in GA metabolism. Investigations of the expressions of rice DELLA-like subfamily genes, GA 3-oxidase family genes and GA 2-oxidase family genes by qRT-PCR showed that OsHox4 played an important role in GA deactivation and signaling by controlling the expression of rice DELLA-like subfamily genes, rice GA 2-oxidase family genes and rice GA 3-oxidase family genes. Our experiment provided an evidence that over-expression of OsHox4 in transgenic rice resulted in a semi-dwarf phenotype that could be fully rescued by application of exogenous GA4. The OsHox4 plays an important role in GA deactivation by controlling the expression of rice DELLA subfamily genes, rice GA 2-oxidase family genes and rice GA 3-oxidase family genes.

Identification and characterization of quantitative trait loci for root elongation by using introgression lines with genetic background of Indica-type rice variety IR64

The root is the sole organ taking up water and nutrients from soils. Hence, root system architecture (RSA) is important for enhancing high-level and stable rice (Oryza sativa L.) production. However, the genetic improvement of RSA has received less attention than yield and yield components. Here, we aimed to identify and characterize quantitative trait loci (QTLs) for RSA by determining the maximum root length (MRL) of seedlings grown hydroponically under various concentrations of NH4+. We used a total of 280 introgression lines (ILs) with an Indica-type variety IR64 genetic background, consisting of ten sibling ILs groups, to detect the QTLs. Greater variation of MRL was found in three sibling ILs groups. In total, five QTLs were detected by single marker analyses: two each on chromosomes 5 and 6 and one on chromosome 7. Among them, the most effective QTL was detected on a segment derived from IR69093-41-2-3-2 (YP5), which was localized to the long-arm of chromosome 6. The QTL, designated as qRL6.4-YP5, concerned in root elongation. MRL and total root length of a near-isogenic line (NIL) for qRL6.4-YP5 were significantly (15.2–24.6 %) higher than those of IR64 over a wide range of NH4+ concentrations. Root number and weight of the NIL were the same as those of IR64. These results indicated that qRL6.4-YP5 was a constitutive QTL for root length in response to change in nitrogen concentrations. To enhance yield potential by improving RSA, qRL6.4-YP5 might help to improve root development in rice molecular breeding programs with marker-assisted selection.