Rice Plant Height Research Articles

Reexamination of silicon effects on rice growth and production under field conditions using a low silicon mutant

Silicon (Si) is a beneficial element for healthy growth and high and sustainable production of rice, but the mode of action of the beneficial effects has not been well understood. We carried out field trials for four years at two different locations to re-examine the effects of Si on the growth and production of rice using a low silicon rice (lsi1) mutant. The mutant accumulated much lower Si at each growth stage compared with the wild-type rice (Oryza sativa L. cv Oochikara), but there was no difference in the accumulation of other nutrients including N, P, and K. Measurements at different growth stages showed that low Si in the mutant hardly affected the tiller number, chlorophyll content (SPAD value), and root growth. The plant height and shoot dry weight of the wild-type rice were slightly higher than those of the mutant at a later growth stage, but the difference was not significant between the two lines. However, grain yield was reduced by 79-98%, depending on year, due to a low Si accumulation in the mutant, which showed the largest effect of Si on rice production among all studies reported so far. Among the yield components, the percentage of filled spikelets was mostly affected, being only 13.9% of the wild-type rice in the mutant. The grain color of the mutant became brown because of excessive transpiration and infection of pathogens. These results indicate that Si increases rice yield mainly by enhancing the fertility of spikelets.

Time-related identification of chromosome regions affecting plant elongation in rice ( Oryza sativa L.)

We investigated the time-related changes of Chromosome Regions that Affect Traits (CRATs) for elongation rate in rice ( Oryza sativa L.) using chromosome segment substitution lines (CSSLs) carrying a single chromosome segment of the cultivar Kasalath ( indica) in a Koshihikari ( japonica) genetic background. The growth period of rice was partitioned into eight stages (each lasting 5–7 days) from 18 days after transplanting, and the elongation rate was determined as the increase of total plant height per time at each growth stage. CRATs for plant elongation rate were determined based on graphical genotype data of CSSLs that showed a significantly higher or lower elongation rate than Koshihikari. In total, 23 CRATs for plant elongation rate were detected, and different CRATs acted at different growth stages. Fifteen CRATs increased the elongation rate through Kasalath alleles, and eight increased it through Koshihikari alleles. These results suggest that plant height in rice is regulated in a stage-specific manner by a variety of genetic mechanisms that control plant elongation rate. Kasalath alleles of PE1-9 increased the elongation rate at an early growth stage (18–25 days after transplanting), while Koshihikari alleles of PE8-3 decreased the elongation rate at a late growth stage (68–74 days after transplanting). In a line that contained both of these CRATs, the elongation rate at the early growth stage was increased without affecting plant height at harvesting. We conclude that stage-specific optimization of plant height in rice may be achieved by combining CRATs that control plant elongation at specific stages.

Multivariate segregation analysis for quantitative traits in line crosses

Segregation analysis is a method of detecting major genes for quantitative traits without using marker information. It serves as an important tool in helping investigators to plan further studies such as quantitative trait loci mapping or more sophisticated genomic analyses. However, current methods of segregation analysis for a single trait typically have low statistical power. We propose a multivariate segregation analysis (MSA) that takes advantage of the correlation structure of multiple quantitative traits to detect major genes. This method not only increases the statistical power, but allows dissection of the genetic architecture underlying the trait complex. In MSA the observed phenotypes of multiple correlated traits are fitted to a multivariate Gaussian mixture model. Model parameters are estimated under the maximum likelihood framework via the expectation-maximization algorithm. The presence of major genes is tested using likelihood ratio test statistics. Pleiotropy is distinguished from close linkage by comparing three possible models using the Bayesian information criterion. Two simulation experiments were performed based on the F(2) mating design. In the first, the statistical properties of MSA under varying heritabilities and sample sizes were investigated and the results compared with those obtained from single-trait analysis. In the second simulation the efficacy of MSA in separating pleiotropy from close linkage was demonstrated. Finally, the new method was applied to real data and detected a major gene responsible for both plant height and tiller number in rice.

Toxicidad del herbicida nicosulfurón en arroz (Oryza sativa L.).

The toxic effects of the herbicide nicosulfuron to rice cv. Milagro Filipino Depurado were determined under greenhouse conditions. Nicosulfuron at 40 and 80 g/ha, the mixture of nicosulfuron + 2,4-D (40 + 480 g/ha) and a nonherbicide treatment were evaluated. Herbicide treatments were applied to plants 3, 10, 17 y 24 days after emergence (DAE). Toxicity was evaluated seven days after application (DAA) and plant height was measured at seven, 15 and 30 DAA; the plant’s dry matter was also quantified at 30 DAA. The highest toxicity was observed in plants treated at three and 10 DAE with nicosulfuron at 80 g/ha and the mixture of nicosulfuron + 2,4-D. The height of rice plants applied with any of the herbicide treatments was significantly lower than that of the non-treated plants at seven and 15 DAA. The nontreatedplants were still significantly taller than the treated plants at 30 DAA, except forthose treated at three DAE with 40 g nicosulfuron or with the mixture nicosulfuron + 2,4-D, at 10 DAE. Plants applied with 40 g nicosulfuron at 10 DAE or later had dry matter productions statistically similar to that of non-treated plants, while plants treated with 80 g nicosulfuron produced the lowest dry matter.

Genetic dissection of developmental behavior of crop growth rate and its relationships with yield and yield related traits in rice

Crop growth rate is a dynamic character that determines the final yield in cereal crops. The objective of the current study is to reveal its genetic basis and to genetically understand its relationships with grain yield and yield related traits like heading date, grain-filling duration, 1000-grain weight and plant height in rice ( Oryza sativa L.). With 258 recombinant inbred lines (RILs) derived from a cross between cv. Lemont and cv. Teqing, time-related QTL mapping was conducted. Eight QTL for crop growth rate were identified at four consecutive growth periods. These QTL individually explained 5–29% of the trait variation. The Teqing alleles increased the trait values at all the four QTL detected before heading, while Lemont contributed alleles to increase the trait values at three of the other four QTL mapped after heading, which was in agreement with the observation that Teqing was the high-value parent before heading, while Lemont became the high-value parent after heading. No common QTL was observed at different growth periods. These results implied that crop growth rate of rice might be controlled by different genes (QTL) during different time intervals. A total of 22 QTL were identified for the other five traits, and the amount of variation explained by individual QTL ranged from 3% to 26%. The interval RM25–CSU754 on chromosome 8 was identified to produce a major effect on multiple traits such as crop growth rate IV, grain yield, heading date, grain-filling duration, plant heights II and IV, which provided a genetic explanation for the close correlations among the traits. The implications of the results for further improvement in rice yield potential were discussed.

Metabolites produced by a wood-rotting fungus shorten rice plant height : their structures and mechanism of action

Metabolites produced by a wood-rotting fungus shorten rice plant height : their structures and mechanism of action

The Plant Architecture of Rice (Oryza sativa)

Plant architecture, a collection of the important agronomic traits that determine grain production in rice, is mainly affected by factors including tillering, plant height and panicle morphology. Recently, significant progress has been made in isolating and collecting of mutants that are defective in rice plant architecture. Although our understanding of the molecular mechanisms that control rice tillering, panicle development and plant height are still limited, new findings have begun to emerge. This review, therefore, summarizes the recent progress in exploring the mechanisms that control rice plant architecture.

Effect of potassium phosphate fertilization on production and emission of methane and its 13C-stable isotope composition in rice microcosms

Rice fields are an important source for atmospheric CH 4, but the effects of fertilization are not well known. We studied the turnover of CH 4 in rice soil microcosms without and with addition of potassium phosphate. Height and tiller number of rice plants were higher in the fertilized than in the unfertilized microcosms. Emission rates of CH 4 were also higher, but porewater concentrations of CH 4 were lower. The δ 13C values of the emitted CH 4 and of the CH 4 in the porewater were both 2–6% higher in the fertilized microcosms than in the control. Potassium phosphate did not affect rate and isotopic signature of CH 4 production in anoxic soil slurries. On the other hand, roots retrieved from fertilized microcosms at the end of incubation exhibited slightly higher CH 4 production rates and slightly higher CH 4- δ 13C values compared to roots from unfertilized plants. Addition of potassium phosphate to excised rice roots generally inhibited CH 4 production and resulted in increasingly lower δ 13C values of the produced CH 4. Fractionation of 13C during plant ventilation (i.e. δ 13C in pore water CH 4 versus CH 4 emitted) was larger in the fertilized microcosms than in the control. Besides plant ventilation, this difference may also have been caused by CH 4 oxidation in the rhizosphere. However, calculation from the isotopic data showed that less than 27% of the produced CH 4 was oxidized. Collectively, our results indicate that potassium phosphate fertilization stimulated CH 4 emission by enhancing root methanogenesis, plant ventilation and/or CH 4 oxidation, resulting in residence times of CH 4 in the porewater in the order of hours.

Effective duration of pesticide-induced susceptibility of rice to brown planthopper (Nilaparvata lugens Stål, Homoptera: Delphacidae), and physiological and biochemical changes in rice plants following pesticide application

The effective durations of pesticide-induced susceptibility of rice to brown planthopper (BPH), Nilaparvata lugens (Stål) (Homoptera: Delphacidae), and physiological and biochemical changes in rice plants following pesticide applications, were studied. The effective duration of the herbicide butachlor on the susceptibility of rice variety Zhengdao 2 to BPH exceeded 16 days. The difference in damage rating between rice plants with pesticide treatments and control plants gradually decreased with days after treatment (DAT). There was a significant correlation between damage rating and DAT. The number of rice tillers at 3 – 10 DAT and plant heights at 7 – 10 DAT declined on Zhengdao 2 with the butachlor treatment. On the other hand, there were no effects of butachlor on damage rating, number of rice tillers and plant height for Xiushui 63. This might be related to tolerance of Xiushui 63 to butachlor. For Zhengdao 2, the fungicide jingganmycin and the insecticide bisultap had a significant influence on BPH damage, number of rice tillers and plant height. In contrast to butachlor, jingganmycin and bisultap had a significant effect on BPH damage to Xiushui 63. However, these two pesticides had no significant effect on the number of rice tillers and plant height of Xiushui 63. In general, the effective duration of butachlor on rice plants was greater than jingganmycin and bisultap. Oxalic acid content and photosynthesis in rice plants declined significantly after jingganmycin and bisultap treatments. These findings are consistent with those of pesticide-susceptibility of rice to BPH. Pesticide-induced susceptibility of rice resistance to BPH counteracts the role of varietal resistance in integrated pest management.

Molecular Dissection of the Relationships among Tiller Number, Plant Height and Heading Date in Rice

Appropriate plant height, tiller number and heading date are important traits for maximizing rice production. In order to understand the genetic basis of the relationships among these three plant traits, we mapped quantitative trait loci (QTLs) using a recombinant inbred population and detected two-locus interactions for plant height and tiller number at two growth stages and for heading date in two years. There were significant negative correlations between tiller number and plant height, and between tiller number at maturity and heading date. A significant positive correlation was observed between heading date and plant height at maturity. A total of 29 QTLs for the three traits were identified over the two years. Results show that QTLs and majority of two-locus interactions for plant height and tiller numbers at 35 days after transplanting were different from those at maturity, indicating that different genes and interactions control the traits at different developmental stages. A large proportion of QTLs and interactions could only be detected in one year, suggesting that QTLs and two-locus interactions for the traits were dependent on the environment. Results suggest that pleiotropy and/or close linkage of genomic regions and pleiotropy of common two-locus combinations may be the genetic basis for the close correlations among the three traits. A QTL with a large effect for heading date, which was located in RG424-RZ667 on chromosome 6, also showed large effects on tiller number and plant height at maturity.

Effects of Cadmium and Mixed Heavy Metals on Rice Growth in Liaoning, China

Joint effects of Cd and other heavy metals (Pb, Cu, Zn and As) on the growth and development of rice plants and the uptake of these heavy metals by rice were studied using the pot-culture method combined with chemical and statistical analyses. The results showed that the growth and development of rice plants were strongly influenced by the double-element combined pollution. There was an average decrease in the height of rice plants of 4.0–5.0 cm, and grain yield was decreased by 20.0–30.0%, compared with the control. The uptake of Cd by rice plants was promoted due to the interactions between Cd and the other heavy metals added to the soil. The Cd concentration in roots, stems/leaves and seeds increased 31.6–47.7, 16.7–61.5 and 19.6–78.6%, respectively. Due to interactions, uptake of Pb, Cu and Zn by roots and stems/leaves was inhibited, accumulation of Pb, Cu and Zn in seeds was increased, uptake of As by roots was promoted and uptake of As by stems/leaves was inhibited. In particular, the upward transporting ability of the heavy metals absorbed by rice plants was significantly increased.

Identification of a new gene controlling plant height in rice using the candidate-gene strategy.

A gene underlying a quantitative trait locus (QTL) controlling plant height on chromosome 1 (QTLph1) in rice ( Oryza sativa L.) was identified using the candidate-gene strategy. First, the function of a targeted gene was analyzed using near isogenic lines (NILs) in which the chromosomal region of a targeted QTL was substituted with that of another line. Second, for physiological information, the candidate gene was selected in the annotation data by the genome sequencing. Physiological analyses of an NIL-expressing QTLph1 (NIL6) suggested that the targeted gene controls plant height by enabling higher amounts of sucrose to be translocated in leaves. The results indicated that the gene for sucrose phosphate synthase (SPS; EC 2.4.1.14), the major limiting enzyme for sucrose synthesis, is a candidate gene for QTLph1 among the annotation results of the region of QTLph1. The higher level of SPS transcripts and the activity of SPS in NIL6 compared to control plants, and the fact that the relative SPS activity per SPS protein content was almost the same between NIL6 and Nipponbare suggested that the higher plant height in NIL6 compared to Nipponbare was due to the high SPS activity in NIL6. In agreement with this hypothesis, transgenic rice plants with a maize SPS gene that had about 3 times the SPS activity of that in Nipponbare (control plants) were significantly taller than Nipponbare from the early growth stage. From these results and the physiological data from NIL6, we concluded that SPS is the targeted gene underlying QTLph1.

Evaluation of the suppression ability of rice (Oryza sativa) on Monochoria vaginalis by measuring photosynthetic photon flux density below rice canopy

Field experiments involving eight cultivars were conducted in 1998 and 16 cultivars in 1999 to study the ability of rice (Oryza sativa L.) to suppress Monochoria vaginalis (Burm. f ) Kunth through light competition. Dry weights of M. vaginalis shoots in early season culture exceeded those in normal season culture of any rice cultivars. The relative photosynthetic photon flux density (R‐PPFD), which was calculated as the ratio of the photosynthetic photon flux density (PPFD) below the rice canopy to that measured above the rice canopy, varied according to rice cultivar. A strong linear correlation was observed between the mean R‐PPFD at 29–35 days after transplanting (DAT) (r2 = 0.80; p < 0.01 in 1998; r2 = 0.63, p < 0.001; and r2 = 0.93, p < 0.001 in 1999), or 36–42 DAT (r2 = 0.66, p < 0.05 in 1998; r2 = 0.72, p < 0.001; and r2 = 0.97, p < 0.001 in 1999), and the dry weight of M. vaginalis shoots at approximately 60 DAT. Data from the three experiments could be pooled into one regression line because intercepts and regression coefficients were not significantly different. The r2 values of the combined regression were highest when R‐PPFD was expressed as the mean of measurements taken during 14 days (from 29 to 42 DAT; r2 = 0.81, p < 0.001). The shortest period for measuring mean R‐PPFD in order to obtain a meaningful relationship with M. vaginalis shoot dry weight was 7 days (from 29 to 35 DAT; r2 = 0.78, p < 0.001). For that same period, relationships between M. vaginalis shoot dry weight at 60 DAT and rice tiller number or leaf area index (LAI) at ground level were weak. However, there were negative relationships between M. vaginalis shoot dry weights at 60 DAT and rice LAI measured 20 cm above the ground, plant heights or rice shoot dry weight, but these coefficients of determination were smaller than those calculated by R‐PPFD for the same period. Thus, the ability of rice to suppress M. vaginalis can be evaluated more accurately by measuring mean R‐PPFD below the rice canopy for 7 days (from 29 to 35 DAT) than by measuring rice LAI, plant height and shoot dry weight.

Rice (Oryza sativa) and Corn (Zea mays) Response to Simulated Drift of Glyphosate and Glufosinate1

Field research was conducted during 3 yr to evaluate response of rice and corn to simulated drift rates representing 12.5, 6.3, 3.2, 1.6, and 0.8% of the usage rates of 1,120 g ai/ha glyphosate (140, 70, 35, 18, and 9 g/ha, respectively) and 420 g ai/ha glufosinate (53, 26, 13, and 4 g/ha, respectively). Early-postemergence applications were made to two- to three-leaf rice and six-leaf corn, and late-postemergence applications to rice at panicle differentiation and to corn at nine-leaf stage (1 wk before tasseling). Crop injury was generally greater for the two highest rates of both herbicides when applied early. Little to no reduction in rice or corn height was observed with glufosinate. Glyphosate consistently reduced rice plant height when the two highest rates were applied early, and heading was delayed 2 to 5 d. In 2 of 3 yr, the highest rate of glyphosate reduced rice yield 99 and 67% when applied early and 54 and 29% when applied late. Germination of rice seeds from glyphosate-treated plants was reduced in 1 of 2 yr and for only the highest rate. For glufosinate, rice yield was reduced 30% and in only one year when applied late at the highest rate. Early application of glyphosate reduced corn yield an average of 22 to 78% for the three highest rates, but only for the highest rate at the late timing (33%). Corn yield was reduced an average of 13 and 11% for the highest rate of glufosinate at the early and late timings, respectively. In greenhouse studies, five rice varieties were equally sensitive, as were five corn varieties, to reduced rates of glyphosate and glufosinate.Nomenclature: Glufosinate; glyphosate; corn, Zea mays L. ‘Asgrow 897’, ‘Dekalb 687’, ‘Mycogen 8460’, ‘Pioneer 3223’, ‘Terral 2930’; rice, Oryza sativa L. ‘Bengal’, ‘Cocodrie’, ‘Cypress’, ‘Drew’, ‘Jefferson’.Additional index words: Crop injury, herbicide drift, off-target movement, rice germination, rice vigor.Abbreviations: DAP, days after plating; DAT, days after treatment.

Características de plantas de cultivares de arroz irrigado relacionadas à habilidade competitiva com plantas concorrentes

Plantas que apresentam rápido crescimento tendem a ocupar precocemente nichos disponíveis, utilizando o espaço de suas vizinhas. Em geral, esses vegetais adquirem prioridade na utilização dos recursos do meio. O objetivo deste trabalho foi avaliar variações em características de crescimento de cultivares de arroz irrigado. Para isso, conduziu-se um experimento em campo na estação de crescimento de 2000/2001, em Cachoeirinha-RS. Investigou-se o comportamento de oito cultivares de arroz, cultivados em presença e ausência de plantas de arroz do cultivar EEA 406, simulando infestação de arroz-vermelho, estabelecida com densidade média de 30 plantas m-2. Entre 15 e 60 dias após a semeadura (DAS), avaliou-se a evolução de área foliar, estatura e massa aérea das plantas de arroz. Com esses dados, calcularam-se razão de área foliar (RAF), taxa de crescimento relativo (TCR) e taxa de assimilação líquida (TAL) dos cultivares. Os cultivares Ligeirinho e XL 6 apresentaram elevadas velocidades de ganho em área foliar, estatura e massa aérea; com isso, alcançaram as maiores coberturas do solo, juntamente com o cultivar IR 841. Por outro lado, os cultivares Bluebelle e Formosa mostraram lento crescimento absoluto no período avaliado, mas, em geral, apresentaram os maiores valores para TCR e TAL.

The sense and antisense expression of gibberellin 20-oxidase gene (rga5) in rice and its effects on GA1 level and agronomic traits

A gibberellin 20-oxidase generga5 was isolated by PCR from genomic DNA of rice (Oryza sativa ssp indica) cultivars ‘Aizizhan’ and ‘Nante’. Compared with the reported OsGA20ox, therga5 was partial-frame-shifted with 11 different amino acids. Then therga5 with CaMV 35S promotor and NOS terminator was inserted into the polylinker site of pCambia1301 to construct sense and antisense gene expressing vectors pSrga5 and pArga5. The transgenic plants were obtained by biolistic bombardment with pSrga5 or pArga5. The transgenic rice plants showed that the overexpression and antisense-expression ofrga5 have remarkable effects on the biological characters of rice. The sense transgenic plants showed heightening with longer spike, more seed-bearing and unaffected flowering, whereas antisense transgenic plants showed dwarfing, early-flowering with slender stem, dark leaf color, shorter leaf and shorter spike. The PCR amplification and Southern blot hybridization showed that therga5 has been integrated into the transgenic rice genome and the transcription ofrga5 was identified by Northern blot hybridization. In the sense transgenic plants the GA1 content increased of about 50%, however, the antisense transgenic rice decreased of 90% approximately compared with control plant ‘Zhonghua 8’. These results demonstrated that therga5 is a functional gene encoding gibberellin 20-oxidase in rice. Over-expressingrga5 significantly increases the endogenous GA1 level and plant height of rice, whereas the expression of antisenserga5 decreases the GA1 level and plant height of rice dramatically.

벼 누른오갈병(Sclerophthora macrospora) 발생이 벼 생육에 미치는 영향 및 병 저항성 품종 검정

전남 나주의 벼 누른오갈병이 발생한 담수직파 포장에서 일미벼를 대상으로 병 발생이 벼 생육에 미치는 영향을 조사하고 품종저항성 검정을 수행하였다. 누른오갈병 발생시 잎에는 퇴록반점이 나타나고 엽장이 짧아지며 벼의 생육이 진행되면서 줄기의 절간신장이 제대로 이루어지지 않아 마디사이가 기형적으로 자라고 출수가 안되거나 기형이삭이 되는 증상을 보였다. 벼 누른오갈병 이병시 초장이 짧아졌고, 분얼수는 최고분얼기 전에 발병주가 적었지만 그 이후에는 발병주가 많았다. 마디수는 발병줄기가 건전줄기에 비해 많은 반면에 마디길이는 짧았다. 발병정도가 심할 수록 단위면적당 이삭수가 적고 등숙율이 낮아 수량이 크게 감소하였다. 유묘를 대상으로 품종 저항성 검정을 실시한 결과, 동진벼, 계화벼가 벼 누른오갈병에 대해서 저항성이었다. It was conducted to investigate the effect of rice downy mildew (RDM) infection to plant growth and yield components in water seeding stage, and to screen of varietal resistance to downy mildew. Being infected by rice downy mildew, chlorotic spot appeared in the leaf and leaf length was shortened. As the infected rice was growing, internode was not elongated properly and was deformed, and then panicle was not arised or mal-formed. Plant height of infected rice was shortened at all growth stage, and while the number of tillers of infected rice was more decreased than that of healthy plant before maximum tillering stage, and that of infected rice was more increased after heading stage. While the number of internode of infected tiller was much increased than that of healthy tiller internode length of infected tiller was shorter. As the rice infected by RDM severely, the number of panicles per square meter and ripening of rice was more decreased and yield of rice was extremely much decreased. As result of the varietal resistance screening with rice seedling, Geyh-wabyeo and Donjinbyeo were resistant varieties to downy mildew.

Competitiveness of Four Rice Cultivars against Barnyardgrass, Echinochloa oryzicola Vasing, with Reference to Root and Shoot Competition

Four cultivars of rice (Oryza sativa L.) different in plant stature were grown on a paddy field, fairly fertile without nitrogen application, with or without barnyard grass, Echinochloa oryzicola Vasing, in the middle of the rice rows. The reduction of the growth variables of the four cultivars by competition with E. oryzicola was examined. The effect of a veneer board inserted in the soil between the rice and barnyardgrass rows was also examined to evaluate the growth reduction by shoot competition (WCS) and root competition (WCr) separately. On the average, the reduction of top dry weight (DWtop) by competition with weed (full competition, WCf) and by WCr increased with the time during the early growth period. Thereafter, the reduction of DWtop by WCr decreased steeply and instead the reduction by WCS increased and became a primary factor of the reduction by WCf in the late growth period. Nitrogen accumulation in the top (Ntop) tended to be reduced at a higher rate than DWtop by WCr. The cultivar difference in the rate of DWt0P reduction by WCf was largest at maturity ranging from 0.22 in Ch86 (very tall indica) to 0.45 in Taichung65d47 (short japonica), and was intermediate in Taichung65 (moderately tall japonica) and Takanari (moderately short indica). The reduction of DWtop and Ntop by WCS in all cultivars almost fully accounted for that by WCf at maturity and closely correlated with the height of rice plant. Although the rate of DWt0P reduction by WCr before heading significantly differed among cultivars (0.13 - 0.28), it did not contribute to the rate of DWtop reduction by WCf at maturity (0.01 - 0.06). These results indicated that shoot competition was a more important factor to cause cultivar difference in the reduction of final biomass by competition with E. oryzicola. Considering its great contribution to WCf during the early growth period especially for Ntop, WCr might be an important factor in the competition with weed of rice cultivars under crucially nitrogen-limited conditions.

Spatial and temporal variability in methane emissions from rice paddies: Implications for assessing regional methane budgets

Growing concern over anthropogenic global climate change has intensified the need to develop accurate budgets of atmospheric methane and other greenhouse gases. Globally, flooded rice cultivation represents a major source of atmospheric methane that is expected to grow with human population. However, current estimates of global methane flux from rice paddies vary by roughly 50%. Understanding the sources of this large variability is critical for developing management strategies for atmospheric methane. Using data collected each growing season from Texas, USA, rice paddies over a 9-year period we examined the spatial and temporal sources of methane flux variability. Using standard deviation of the mean methane flux as a measured of variability, we found that accounting for rice plant height and grain yield reduced spatial variability from 25.2 to 17.7% of the mean. Temporal variability over the entire 9-year data set was 49% of the mean, 71% of which was explained by variations in average rice plant height and total nitrogen fertilizer application. The magnitude of temporal and spatial variability suggests that reliance on single-field studies for determination of global methane budgets may be questionable.

Modification of Rice Plant Height by Suppressing the Height-Controlling Gene, D18, in Rice.

Gibberellin (GA) 3β-hydroxylase catalyzes the final step of active GA synthesis in plants. In rice, the enzyme is encoded by at least two genes (OsGA3ox1 and OsGA3ox2) with differential patterns of expression. Previously, we reported that the OsGA3ox2 gene is identical with the D18 gene. The loss-of-function mutants of D18 designated as d18-AD (Akibare waisei), d18-Id18h (housetsu waisei), and d18-dy (Waito-C) show severe dwarfism caused by the decrease of the level of active GA, GA1. The gene encodes GA 3β-hydroxylase that catalyzes the reaction from GA20 to GA1 and its expression is also regulated by active GA through a feedback mechanism, suggesting that the step catalyzed by the enzyme may be a key step for regulating the level of active GA. To determine the possibility of reducing the height of rice through regulation of the level of active GA, we produced transgenic rice plants expressing the antisense of D18 cDNA. Plants expressing the antisense showed a semi-dwarf phenotype relative to the control plants carrying the vector only. The antisense plants with the semi-dwarf phenotype showed a reduced level of D18 mRNA. In contrast to the reduced level of D18 mRNA, the plants induced a higher expression level of OsGA20ox1, which encodes GA 20-oxidase catalyzing the step from GA53 to GA20 in the GA biosynthetic pathway. These results demonstrate that the height of rice can be controlled by manipulation of the GA 3β-hydroxylase expression through the decrease in the active GA level.