Studies on culture ability of Glabrous rice(Oryza sativa L.)

Glabrous rice is characterized by its smoothand hairness leaves and husks,mainly dis- tributed in America,Africa,and Yunnan andGuizhou provinces of China.It has the charac- teristics of strong stem,high endurance tolodging,good compatibility,high grain quali-ty,and high yield,and is propitious to themachanized harvest.The Glabrous rice hasbeen proved to be plant population of superior- ity,which could be used as germplasm re-     

Detecting ALS and ACCase herbicide tolerant accession of Echinochloa oryzoides (Ard.) Fritsch. in rice (Oryza sativa L.) fields

Inconsistent control of Echinochloa oryzoides has been reported repeatedly by farmers in the major rice growing area of Turkey. Greenhouse studies confirmed the existence of cross and multiple herbicide tolerance of E. oryzoides accessions including acetolactate synthase (penoxsulam, bispyribac-sodium) and acetyl CoA carboxylase (cyhalofob-butyl) inhibiting herbicides. Comparison of 95% lower confidence intervals of ED₉₀ derived from log-logistic dose–response curves, and twice the recommended field rates of the herbicides showed some, but not distinct separation of susceptible and tolerant accessions. We used a novel method to separate heterogeneous data without a priori knowledge of grouping into more than one group. On the basis of the distribution of ED₉₀ it was possible to identify two distinct groups of the 172 accessions tested, 78% were not controlled by ALS inhibitors (penoxsulam, and bispyribac-sodium) at recommended field rates; and 38% were not controlled by the ACCase Inhibitor (cyhalofob-butyl) at twice the field rates. The effective response level of ED₉₀ resulted in 64 and 14 tolerant accessions to ALS and ACCase, respectively. Fourteen accessions showed multiple resistances to ALS and ACCase Inhibitors.Some of the accessions were strongly tolerant to both herbicide modes of action and had 100% survival even at 6 times the recommended rates. Most of these tolerant accessions were from Marmara region, predominantly in Edirne and Balıkesir, which are the regions without any crop rotation.     

An in planta, Agrobacterium-mediated transient gene expression method for inducing gene silencing in rice (Oryza sativa L.) leaves

Background

Although the genetic structure of rice germplasm has been characterized worldwide, few studies investigated germplasm from Thailand, the world’s largest exporter of rice. Thailand and the International Rice Research Institute (IRRI) have diverse collections of rice germplasm, which could be used to develop breeding lines with desirable traits. This study aimed to investigate the level of genetic diversity and structures of Thai and selected IRRI germplasm. Understanding the genetic structure and relationships among these germplasm will be useful for parent selection used in rice breeding programs.

Results

From the 98 InDel markers tested for single copy and polymorphism, 19 markers were used to evaluate 43 Thai and 57 IRRI germplasm, including improved cultivars, breeding lines, landraces, and 5 other Oryza species. The Thai accessions were selected from all rice ecologies such as irrigated, deep water, upland, and rainfed lowland ecosystems. The IRRI accessions were groups of germplasm having agronomic desirable traits, including temperature-sensitive genetic male sterility (TGMS), new plant type, early flowering, and biotic and abiotic stress resistances. Most of the InDel markers were genes with diverse functions. These markers produced the total of 127 alleles for all loci, with a mean of 6.68 alleles per locus, and a mean Polymorphic Information Content (PIC) of 0.440. Genetic diversity of Thai rice were 0.3665, 0.4479 and 0.3972 for improved cultivars, breeding lines, and landraces, respectively, while genetic diversity of IRRI improved and breeding lines were 0.3272 and 0.2970, respectively. Cluster, structure, and differentiation analyses showed six distinct groups: japonica, TGMS, deep-water, IRRI germplasm, Thai landraces and breeding lines, and other Oryza species.

Conclusions

Thai and IRRI germplasm were significantly different. Thus, they can be used to broaden the genetic base and trait improvements. Cluster, structure, and differentiation analyses showed concordant results having six distinct groups, in agreement with their development, and ecologies.     

Effect of rice establishment methods on weedy rice (Oryza sativa L.) infestation and grain yield of cultivated rice (O. sativa L.) in Sri Lanka

Weedy rice is a great threat to rice production in Sri Lanka. Selective herbicides to manage weedy rice in conventional rice cultivars are not available in Sri Lanka. In the absence of appropriate chemical control measures, cultural approaches may help to achieve effective control of weedy rice. A study was conducted in two consecutive seasons in farmers' fields at three sites (Atalla, Samanthurai, and Girithale villages) in Sri Lanka to evaluate the effect of different establishment methods (farmers' practice, random broadcast, row seeding, seedling broadcast, and transplanted rice) on weedy rice infestation and rice yield. The farmers' practice had a higher number of weedy rice panicles (60–80 m⁻²) than the random broadcast (39–48 panicles m⁻²), seedling broadcast (3–15 panicles m⁻²), and transplanted rice (1.3–3.0 panicles m⁻²) methods. The use of clean rice seeds in the random broadcast method reduced weedy rice seed production by 29–41% compared with the farmers' practice (0.6–2.0 t ha⁻¹). Compared with the farmers' practice, the seedling broadcast method reduced weedy rice seed production by 71–87% and transplanted rice by 95–98%; and increased rice yield by 27–49% (7.5–9.1 t ha⁻¹). At all three sites, the farmers' practice resulted in the lowest grain yield (5.1–6.7 t ha⁻¹). Compared with the farmers' practice, the random broadcast and row seeding methods increased rice yield by up to 21% and 31%, respectively. The findings suggest that the use of clean rice seeds, the use of a row-seeded crop, and the adoption of different rice planting methods may help to suppress the spread of weedy rice.     

Glutelin is partially degraded in globulin-less mutants of rice (Oryza sativa L.)

Multigenic glutelins and monogenic globulin are major storage proteins accumulating in vacuole-derived protein body (PB-II) of rice (Oryza sativa L.) seeds. Because their interplay in PB-II formation was scarcely known, the effect of globulin-less mutation on glutelin accumulation was investigated. In globulin-less mutants, no phenotypic defect was found in seed and plant growth, while PB-II was deformed and apparent glutelin composition was changed, producing new glutelin α polypeptides X1–X5. 2D-PAGE of different combinations of globulin-less and glutelin subunit mutations suggested that the X1/X2, X3, and X4/X5 were derived from glutelin GluB1/GluB2/GluB4, GluA3, and GluA1/GluA2 subunits, respectively. Western blot with glutelin GluB4 subunit-specific and its variable region discriminable antibodies indicated at least in part the new spots X1/X2 are partially degraded products of GluB4 α polypeptides by the removal of 2–39 residues from C-terminus. Time course experiments with maturing seeds indicated the partial degradation of GluB4 occurred earlier (from 7 days after flowering) and higher than that of GluA1/GluA2. Considering the above results together with the fact that globulin accumulates at the periphery of PB-II and its absence produces deformed PB-II, globulin protects glutelins from proteinase digestion and thereby facilitates stable glutelin accumulation.     

Molecular genetic mapping of quantitative trait loci for milling quality in rice (Oryza sativa L.)

Identification and mapping of genomic regions controlling quantitative trait loci (QTLs) was undertaken to determine the genomic regions associated with milling traits in rice to facilitate breeding of new rice varieties with high milling quality. The recombinant inbred (RI) population used was derived from cross of a japonica variety, ‘Asominori’, with an indica variety, ‘IR24’ through 289 RFLP markers. Three milling traits, namely, brown rice percentage (BRP), milled rice percentage (MRP), and milled head rice percentage (MHP), which are the main indicators of milling quality in rice, were estimated for each RI line and their parental varieties. Continuous distributions and transgressive segregations of three milling traits were observed in the RI population, showing that the three traits were quantitatively inherited. Two QTLs (qBRP-9 and qBRP-10) for BRP were identified and mapped to chromosomes 9 and 10, and explained 7.2 and 21.3% of the total phenotype variation, respectively. Two QTLs (qMRP-11 and qMRP-12) governing MRP were detected and mapped to chromosomes 11 and 12, accounted for 12.2 and 7.7% of total phenotype variation, respectively. In addition, three QTLs (qMHP-1, qMHP-3 and qMHP-5) controlling MHP were observed and mapped to chromosomes 1, 3 and 5, and explained 16.0, 22.1 and 8.7% of the total phenotype variation, respectively. Among them, five QTLs (qBRP-9, qBRP-10, qMRP-11, qMHP-3 and qMHP-5) from japonica parent, Asominori, and two QTLs (qMRP-12, qMHP-1) from indica IR24 can improve milling quality in rice. The results and the tightly linked molecular markers that flank the QTL will be useful in breeding for improvement of milling quality in rice.     

Competitiveness of rice (Oryza sativa L.) cultivars against Echinochloa crus-galli (L.) Beauv. in water-seeded production systems

Developing more competitive rice cultivars could help improve weed management and reduce dependency on herbicides. To achieve this goal, an understanding of key traits related to competitiveness is critical. Experiments were conducted at Gelemen and Bafra districts of Samsun province in Turkey between 2008 and 2009 to measure the competitiveness of rice cultivars against Echinochloa crus-galli, a problematic weed in rice fields. Five rice cultivars (Osmancık, Kızılırmak, Karadeniz, Koral and Neğiş) and five E. crus-galli densities (0, 5, 10, 20, and 30 plants m⁻²) were used. Koral produced significantly more tillers than the other cultivars irrespective of E. crus-galli densities and reduced E. crus-galli tiller production by about 29.5% at Gelemen and 15.8% at Bafra at the highest weed density. E. crus-galli interference reduced rice height and there was a density dependent relationship. Koral was the most competitive cultivar; it maintained high biomass accumulation in early growth stages and suffered smaller reductions in plant height in the presence of E. crus-galli, compared to the other cultivars. In the absence of weed competition, Koral and Neğiş produced the highest yields at both locations. Stepwise regression analyses of the combined data from both years showed tillering capacity, early growth crop biomass, and plant height were critical traits related to competitiveness. These traits should be considered by plant breeders in their efforts to develop rice cultivars with enhanced competitiveness against weeds. Development of such cultivars could substantially reduce herbicide and labor inputs for rice production.     

Genetic architecture, inter-relationship and selection criteria for yield improvement in rice (Oryza sativa L.)

This study has been conducted to determine the extent of genetic association between yield of Rice (Oryza sativa L.) and its components. The present experiment was carried out with 40 Rice (Oryza sativa L.) genotypes which were evaluated in a randomized block design with 3 replications during wet season of 2007 and 2008. Results showed that sufficient amount of variability was found in the entire gene pool for all traits studied. Higher magnitude of genotypic and phenotypic coefficients of variation was recorded for seed yield, harvest index, biological yield, number of spikelets per panicle, flag leaf length, plant height and number of tillers indicates that these characters are least influence by environment. High heritability coupled with high genetic advance as percent of mean was registered for seed yield, harvest index, number of spikelets per panicle, biological yield and flag leaf length, suggesting preponderance of additive gene action in the expression of these characters. Grain yield was significantly and positively associated with harvest index, number of tillers per hill, number of panicle per plant, panicle length, number of spikelet's per panicle and test weight at both genotypic and phenotypic levels. Path coefficient analysis revealed that harvest index, biological yield, number of tillers per hill, panicle length, number of spikelets per panicle, plant height and test weight had direct positive effect on seed yield, indicating these are the main contributors to yield. From this study it may be concluded that harvest index, number of tillers per hill, panicle length and number of spikelet per panicle and test weight are the most important characters that contributed directly to yield. Thus, these characters may serve selection criteria for improving genetic potential of rice.     

Critical nitrogen concentrations: implications for high-yielding rice (Oryza sativa L.) cultivars in the tropics

The critical nitrogen concentration of a plant can be defined as the minimum nitrogen concentration required for maximum growth rate at any time. It has been suggested that the relationship between the critical N concentration and dry matter per unit ground area for a wide range of crops is the same and is independent of climatic zone. Results presented in this paper support the concept of a critical N-dilution curve for yield of rice (Oryza sativa L.), which may be independent of climatic zone. The similarity between the nitrogen dilution curves for temperate and tropical environments indicates that there is no intrinsic difference in the ratio of carbon-to-nitrogen capture in those environments even though the final aboveground biomasses differed. Both the rate and duration of resource capture are probably limiting yields in tropical environments. In order to break through the current ceiling-yield barrier of approximately 10 t grain ha⁻¹ in the tropics, superior germplasm must be lodging resistant and capable of acquiring 144 kg N ha⁻¹ (N_0.5) in the first 35 days following transplanting. An examination of the rates of nitrogen acquisition indicated that more emphasis must be placed on providing sufficient nitrogen during the early stage of crop growth if higher yields are to be obtained. The time course of nitrogen accumulation by the aboveground biomass was calculated for weights greater than 1 t ha⁻¹; at weights less than this there were insufficient data to make calculations. At weights of aboveground biomass greater than 1 t ha⁻¹, the rate of nitrogen acquisition per unit ground area declined. The decline probably reflected a lowering in crop demand for soil nitrogen caused by the internal cycling of nitrogen from aging to young developing tissues; roots' age may also play a part in the decline. The estimated rate of demand for nitrogen by the panicle exceeded the rate at which the aboveground biomass acquired it, emphasizing the importance of having a large `reservoir' of nitrogen in vegetative tissues. Such a reservoir would ensure that the nitrogen demand of the panicle could be met without causing the photosynthetic capacity of the crop to prematurely lose its ability to meet the carbohydrate demand of the panicle.     

Genetic expression and effects of the rolled leaf gene Rl(t)in hybrid rice (Oryza sativa L.)

We constructed a near isogenic line of rolled leaf gene Rl(t), which expressed incompletely dominance for the character of rolled leaf(RL), with genetic background of Zhenshan 97B. Using RL Zhenshan 97B and the original Zhenshan 97B as the female parents,and Minghui 63 and Yanhui 559 as the male parents, crosses of RL Shanyou 63 (RS63) and Shanyou 63(S63), RL Shanyou 559 ( RS559) and Shanyou 559 (S559) were made. Inheritance and effects of Rl(t) in hybrid rice were studied at the flowering and at the 20 d after flowering, respectively. Results were as follows:     

Adaptation of rice (Oryza sativa L.) genotypes in the rainfed lowlands of Lao PDR

Genotype by environment (G×E) interactions for grain yield were investigated in 14 rice genotypes across eight rainfed lowland field environments in Lao PDR, in order to identify stable adapted cultivars for improved farmer livelihood and food security. G×E accounted for 20.3% of the total variance, with three vectors from ordination analysis accounting for 75.1% of the G×E-SS, in 6 genotype?×?6 environment groups. PCA1 indicated water-limited yield potential, PCA2 pre-flowering stress and PCA3 post-flowering stress. Genotype groups (G1–G6) differed in adaptation to these environments. G5 (VT450-2 and TSN9) were widely adapted and high-yielding. G6 (TDK11 and TDK37) were also high-yielding, topping the rankings in three environment groups, but yielded less in Phalanxay 2012 and Phalanxay 2011, where their phenology was unstable under stress. Other genotype groups showed specific adaptations, but failed to exceed yields of G5 and G6. Hence, VT450-2 and TSN9 (G5) were the preferred genotypes for rainfed lowland in southern Lao PDR, due to their high and stable grain yields. Stability in flowering time and high yield in rainfall deficit were desirable traits for improved farmer livelihood and food security.     

Weed management challenges in rice (Oryza sativa L.) for food security in Bhutan: A review

Rice is the most important and staple cereal in Bhutan, currently grown over an area of 19,549 hectares with a total production of 77,038 tonnes. However, its yield is limited in certain regions due to weed competition with losses of up to 50% reported through infestation from both annual and perennial weeds. In this article, we describe the current weed management practices in rice in Bhutan and identify challenges and prospects to guide future weed control research given that weed science in Bhutan is in its infancy. Generally, the most common form of weed control is hand weeding. However, herbicide use is also increasing as farmers face labour shortages on farms and realize the benefits of herbicides, especially in reducing the time taken to weed crops. But the continued use of the single chemical butachlor is a concern given the possible development of herbicide resistance. Research priorities for weed management in rice in Bhutan include a systematic assessment of crop yield losses; prioritization of weed importance and species shifts; mechanical and cultural alternatives to hand weeding; herbicide resistance testing and management; collective community approaches to area-wide management; and weed management options to suit alternative rice production systems. The ecology and management of the perennial semi-aquatic Potamogeton distinctus needs serious attention owing to its prevalence in major rice areas and potential alone to cause significant yield losses of up to 37%. The successful experiences and challenges in neighbouring Asian countries should also help to guide future weed control research in Bhutan.     

Analysis of QTLs for seed low temperature germinability and anoxia germinability in rice (Oryza sativa L.)

Direct seeding instead of transplanting for rice (Oryza sativa L.) has increasingly been used in northern and eastern China because of labor and cost saving. However, poor germinability is still one of the major problems faced in the adoption of direct seeding under low temperature (low temperature germinability: LTG) and anoxia (anoxia germinability: AG) condition. To gain an understanding of the genetic control of seed germinability under these unfavourable conditions, two rice lines, USSR5 (japonica type) and N22 (indica type) and F₂ individuals derived from the cross USSR5 × N22 were tested for LTG and AG. USSR5 and N22 differ significantly for both LTG and AG. The LTG of the F₂ individuals ranged from 0 to 100% after a 10 days incubation. AG ranged from 0.0 to 4.0 cm shoot length. Based on segregation in the F₂ population, a linkage map was constructed using 121 SSR markers. The map covered 1821.5 cM, with a mean inter-marker distance of 16.7 cM. Eleven putative QTLs for LTG were detected, one on each of chromosomes 3–5, 7, 9–11, and four on chromosome 5. The USSR5 alleles in all these QTLs acted to increase LTG. Two QTLs for AG were located on chromosomes 5 and 11, respectively, at both of which the USSR5 alleles acted to increase AG. We propose that USSR5 could make a major contribution to improving LTG and AG in rice breeding programs.     

Molecular mapping of quantitative trait loci for zinc toxicity tolerance in rice seedling (Oryza sativa L.)

Excess zinc harms the growth of rice plants and zinc toxicity can easily occur in acid soils. The aim of the study was to map quantitative trait loci (QTLs) in rice for tolerance to zinc toxicity, using a recombinant inbred (RI) population derived from the cross of a japonica variety (Asominori: relatively tolerant to Zn²⁺ toxicity) with an indica variety (IR24, relatively susceptible), through 289 RFLP markers. The index scores of damage (representing Zn²⁺ toxicity tolerance), after irrigating rice seedlings with a 1000-ppm Zn²⁺ solution for 20 successive days, were examined for each RI line and its parental varieties. Continuous distributions and transgressive segregations of the index scores were observed in the RI population, suggesting that Zn²⁺ toxicity tolerance was a quantitatively inherited trait. Three QTLs for Zn²⁺ toxicity tolerance were detected on chromosomes 1, 3 and 10 and explained 21.9, 8.9 and 7.6%, respectively, of the total phenotypic variation. The results and the tightly linked molecular markers that flank the QTLs, detected in this study, will be useful in improving Zn²⁺ tolerance in rice. In addition, the genomic positions between QTLs for Zn²⁺ toxicity tolerance and the QTLs for other metal (Fe²⁺, Mn²⁺, Al³⁺) toxicity tolerances, from previous studies, are discussed.     

Variations of endoreduplication and its potential contribution to endosperm development in rice (Oryza sativa L.)

ABSTRACT

Endoreduplication is the phenomenon by which cells increase their ploidy. Endoreduplication is initiated by the transition from the mitotic cell cycle to the endocycle, in which DNA replication occurs without a subsequent chromosome separation and cytokinesis, and is enhanced by endocycle reiteration. This process appears to play an important role in endosperm development, but the characteristics of endoreduplication in the endosperm of rice (Oryza sativa) remain unclear. To elucidate the features and variations of endoreduplication in rice endosperm, endoreduplication progression in the developing endosperm was compared among 10 cultivars based on flow cytometry and fluorescence microscopy. The flow cytometric analysis detected significant differences among 10 cultivars in the following three parameters: mean ploidy of all nuclei, the proportion of nuclei ≥6C (%E, an estimate of the initiation of the endocycle), and the mean ploidy of nuclei ≥6C (E6P, an estimate of the reiteration of the endocycle). However, no significant correlation between %E and E6P was observed, suggesting that the initiation and reiteration of the endocycle are independently regulated. Fluorescence microscopy revealed that the ploidy of the nuclei was higher in the intermediate region than in the central and peripheral regions of the endosperm. Cells with a higher ploidy were larger in the developing endosperm. Furthermore, the mean ploidy in the developing endosperm was significantly correlated with the mean cell size in the mature endosperm. These results indicate that endoreduplication progression in the endosperm differed significantly among the 10 rice cultivars and such differences may influence endosperm cell size.     

Callus induction and in vitro plant regeneration of rice (Oryza sativa L.) under various conditions

The objective of the present study was to develop an effective protocol for optimum callus induction and complete plant regeneration for four varieties of rice (Oryza sativa L.) i.e., Super Basmati, Basmati-370, Basmati-371 and Fakhre Malakand. Calli were induced from mature seed scutelum. The Murashige and Skoog (MS) and Chu's N6 media containing hormone 2, 4-D (2, 4-Dichlorophenoxy acetic acid) in different concentrations were used for callus induction. Fakhre Malakand produced maximum calli on N6 media containing 3 mg L(-1) 2,4-D. while other three varieties showed maximum callus induction on N6 media containing 2.5 mg L(-1) 2,4-D. N6 media was found better than MS media for callus induction. For complete plant regeneration the calli of two varieties i.e., Basmati-370 and Basmati-371 were plated on N6 media containing different concentrations of NAA (1-Naphthalene acetic acid) and BAP (6-benzyl aminopurine). The maximum regeneration frequency (%) was observed on N6 media containing NAA 1 mg L(-1) and BAP 2.5 mg L(-1). It took 27-30 days for the callus to regenerate into a complete plant. Basmati-370 produced 4-7 plantlets per callus whereas Basmati-371 produced 4-8 plantlets per callus with regeneration frequencies of 61 and 69%, respectively.