Effect of SWD irrigation on photosynthesis and grain yield of rice (Oryza sativa L.)

A study was conducted with the objective to determine the influence of (shallow water depth with wetting and drying) SWD on leaf photosynthesis of rice plants under field conditions. Experiments using SWD and traditional irrigations (TRI) were carried out at three transplanting densities, namely D1 (7.5 plants/m²), D2 (13.5 plants/m²) and D3 (19.5 plants/m²) with or without the addition of organic manure (0 and 15 t/ha). A significant increase in leaf net photosynthetic rate by SWD was observed with portable photosynthesis systems in two independent experiments. At both flowering and 20 DAF stages, photosynthetic rate was increased by 14.8% and 33.2% with D2 compared to control. SWD significantly increased specific leaf weight by 17.0% and 11.8% over the control at flowering and 20 DAF stages, respectively. LAI of D2 under SWD was significantly increased by 57.4% at 20 DAF. In addition, SWD with D2 significantly increased the leaf dry weight (DW) at both growing stages. At all the three densities, SWD increased the leaf N content and the increase was 18.9% at D2 density compared with the conventional control. In SWD irrigation, the leaf net photosynthetic rate was positively correlated with the leaf N content (R² = 0.9413), and the stomatal conductance was also positively correlated with leaf N content (R² = 0.7359). SWD enhanced sink size by increasing both panicle number and spikelet number per panicle. The increase in spikelet number per panicle was more pronounced in the 15 t ha⁻¹ manure treatment than in the zero-manure treatment. Grain yield was also significantly increased by SWD, with an average increase of 10% across all treatments. SWD with D2 had the highest grain yield under the both cultivars with or without 15 t ha⁻¹ manure treatment, which was 14.7% or 13.9% increase for Liangyoupeijiu and 11.3% or 11.2% for Zhongyou 6 over the control, respectively.     

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.     

Study of water stress effects in different growth stages on yield and yield components of different rice (Oryza sativa L.) cultivars

A field experiment was conducted during 2001-2003 to evaluate the effect of water stress on the yield and yield components of four rice cultivars commonly grown in Mazandaran province, Iran. In northern Iran irrigated lowland rice usually experiences water deficit during the growing season include of land preparation time, planting, tillering stage, flowering and grain filing period. Recently drought affected 20 of 28 provinces in Iran; with the southeastern, central and eastern parts of the country being most severely affected. The local and improved cultivars used were Tarom, Khazar, Fajr and Nemat. The different water stress conditions were water stress during vegetative, flowering and grain filling stages and well watered was the control. Water stress at vegetative stage significantly reduced plant height of all cultivars. Water stress at flowering stage had a greater grain yield reduction than water stress at other times. The reduction of grain yield largely resulted from the reduction in fertile panicle and filled grain percentage. Water deficit during vegetative, flowering and grain filling stages reduced mean grain yield by 21, 50 and 21% on average in comparison to control respectively. The yield advantage of two semidwarf varieties, Fajr and Nemat, were not maintained under drought stress. Total biomass, harvest index, plant height, filled grain, unfilled grain and 1000 grain weight were reduced under water stress in all cultivars. Water stress at vegetative stage effectively reduced total biomass due to decrease of photosynthesis rate and dry matter accumulation.     

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.     

Growth and yield formation of rice (Oryza sativa L.) in the water-saving ground cover rice production system (GCRPS)

A new water-saving ‘Ground Cover Rice Production System’ (GCRPS) was evaluated in 2001 and 2002 near Beijing, North China. Using GCRPS, lowland rice was cultivated without a standing water layer during the entire growth period and plots were irrigated when soil water tension was below 15 kPa (approximately 90% water holding capacity). In order to prevent soil evaporation, the soil surface was covered with 14 μm thick plastic film (GCRPS_Plastic) or mulched with straw (GCRPS_Straw). In a third GCRPS treatment the soil was left uncovered (GCRPS_Bare). These treatments were compared with lowland rice cultivated under traditional paddy conditions (Paddy control). In an additional treatment with bare soil, one aerobic rice variety was cultivated. Compared to Paddy control, only 32–54% of irrigation water was applied in GCRPS treatments. Plants in GCRPS were smaller, developed fewer panicles and had a smaller leaf area index compared to Paddy control. Yield was significantly less in GCRPS_Bare and GCRPS_Straw compared to Paddy control in both years, while yield in GCRPS_Plastic was only 8% less than the Paddy control yield in 2002. Water-use efficiency (WUE, gram grain yield per litre water input) in GCRPS_Plastic was higher (0.35) than in Paddy control (0.23). Grain yield was highly significantly correlated with maximum leaf area index and leaf area index duration. Among yield components, the number of productive tillers had the greatest positive effect on yield, while the number of grains per panicle, thousand-grain weight and harvest index remained almost unaffected. Under uncovered condition, the aerobic rice variety had a significantly higher harvest index (HI), yield, and WUE compared to the lowland rice variety (GCRPS_Bare). The experiment demonstrates that GCRPS has potential to save substantial amounts of water at relatively minor yield penalties, if stress factors such as low soil temperature, water deficit, and nutrient deficiencies during the vegetative growth stage are avoided by suitable management practices.     

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-     

Estimation of combining ability for yield and yield components in rice (Oryza sativa L.) cultivars using diallel cross

In order to estimate combining ability and gene action of a number of rice cultivars, a 5 x 5 half a diallel cross genetic design has been used. Parents and their hybrids have been evaluated in a randomized complete block design with 3 replicates for yield and 6 yield components in 2007 in Rice Research Station of Iran-Amol. Mean squares of genotypes for all traits were highly significant (p < 0.01). Significant mean squares of combining ability for all traits showed additive and non-additive effects in control of the related traits. Having nonsignificant MS(GCA)/MS(SCA) ratio for all traits but 1000-grain weight show higher importance of nonadditive effects in comparison with additive effects of controlling genes. High relative importance of specific combining ability indicated that all traits but 1000-grain weight are highly affected by impacts of specific combining ability. Generally, Dasht, Neda and Binam were the best parents for general combining ability and Binam x IR62871-175-1-10 and Mashhad Domsiah x Binam were the best hybrids for grain yield and its components.     

Genotypic differences in grain yield of transplanted and direct-seeded rainfed lowland rice (Oryza sativa L.) in northeastern Thailand

We evaluated the genotypic differences in grain yield of 14 rice (Oryza sativa L.) genotypes with different phenology under four growing conditions: transplanting (TP) or direct-seeding (DS) in a toposequentially lower (with favorable water conditions) or upper (drought at around flowering stage) field at Ubon Ratchathani, northeastern Thailand. Thirteen of the genotypes – five early-maturing, four intermediate, and four late – had been bred for rainfed lowlands in northern and northeastern Thailand. IR24, a semi-dwarf, high-yielding, and early-maturing genotype bred for irrigated lowlands, was included for comparison. Genotypic differences in grain yield were significant in a combined analysis of all 4 growing conditions, and both high sink size (spikelet number per area) and high ripened grain percentage were associated with high yield. IR24 did not out-yield the rainfed-lowland genotypes, and its yield was particularly low in DS, owing to poor shoot dry matter production and low spikelet number per panicle. In the lower field, the interaction between cultivation method and genotype was also significant. In the lower field, late maturity was more strongly related to high shoot dry weight at maturity in TP than in DS; some of the early- to intermediate-maturing genotypes in DS produced shoot dry weights at maturity that were comparable to those of the late-maturing genotypes. High shoot dry matter production and large spikelet number per panicle were associated with high grain yield in DS genotypes in the lower field, whereas in TP genotypes with large numbers of panicles were required for high grain yield. Although the field location–genotype interaction and the field location–cultivation method–genotype interaction were not significant, regression analysis showed that late-maturing genotypes yielded less than earlier maturing genotypes, owing to the smaller ripened grain percentage resulting from late-season drought, in the upper field but not in the lower field. The presence of a trade-off between number of ripened grains and grain size in the lower field indicated the possibility of increasing the yield in rainfed-lowland genotypes by increasing assimilation capacity during grain filling. Phenology is important in the development of higher-yielding genotypes for different cultivation methods and different toposequential positions.     

Genetic analysis of transparency and chalkiness area at different filling stages of rice (Oryza sativa L.)

Seven cytoplasmic male sterile lines and five restorer lines of indica rice (Oryza sativa L.) were used to analyze genetic effects on transparency and chalkiness area at four filling stages. A developmental genetic model for quantitative traits of triploid endosperm in cereal crops were used for the data analysis. The unconditional analysis showed that the accumulated genetic effects of genes expressed from the initial time (at flowering and fertilization) to the filling time t were all significant for transparency and chalkiness area. These results indicated that the genetic effects of the triploid endosperm, cytoplasmic and diploid maternal plant were all of importance for both traits at various filling stages, especially for maternal additive and dominance effects on transparency. The relatively high endosperm and maternal additive effects on transparency and chalkiness area indicated that the two traits could be improved by selection in early generations. From the conditional analysis for the net genetic effects of genes expressed during time t−1 to time t, new expression of genes in endosperm, cytoplasm and maternal plant for transparency and chalkiness area was found at most of the filling stages, especially from 8 to 14 days after flowering for transparency and from 1 to 14 days after flowering for chalkiness area. Predicted genetic effects and conditional genetic effects at different filling stages showed that transparency and chalkiness area of offspring could be improved by using some parents, such as Zuo 5, because of their better endosperm additive and cytoplasmic effects.     

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.     

Yield response of rice (Oryza sativa L.) genotypes to different types of drought under rainfed lowlands: Part 1. Grain yield and yield components

Responses of rice genotypes to drought stress may be different when characteristics of the drought stress environments differ. The performance of 128 genotypes was examined under irrigation and four different types of drought stress, to determine genotypic consistency in yield and factors determining yields under different drought stress conditions. The different drought conditions were mild drought during grain filling, short and severe drought at flowering, prolonged severe drought during the reproductive to grain filling, and prolonged mild drought during vegetative and grain filling.Genotypic grain yield under mild stress conditions was associated with yield under irrigated conditions, indicating the importance of potential yield in environments where the yield reduction was less than 50%. However, yields under irrigated conditions differed over time and locations.Under prolonged or severe drought conditions, flowering time was an important determinant of grain yield. Earlier flowering genotypes escaped the severe stress and had higher grain yields indicating large genotype by environment (G×E) interactions which have implications for plant breeding even for mild stress. It is suggested that variations in flowering time, potential yields and drought patterns need to be considered for development of drought-resistant cultivars using specific physiological traits.     

Water regimes: an approach of mitigation arsenic in summer rice (Oryza sativa L.) under different topo sequences on arsenic-contaminated soils of Bengal delta

Arsenic (As)-contaminated groundwater has been widely used in agricultural purposes especially for summer rice cultivation in South East Asia. Therefore, the present experiments were carried out at low (diara) and medium land topo sequences with the eight water regimes to reduce the As accumulation in summer rice (Oryza sativa L.). Experimental results revealed that the intermittent ponding of 2–4 days after disappearance (DAD) were significantly reduced the As accumulation in root, stem, leaves, flag leaf, husk, and grain (21.86–31.78, 23.55–37.20, 14.83–30.93, 23.53–31.19, 21.33–28.19, and 22.98–25.37 %, respectively), which was followed by aerobic rice (21.34–22.08, 22.49–30.72, 12.21–23.02, 22.06–27.52, 20.14–23.94, and 22.12–22.30 %, respectively), and saturation of top soil (17.43–17.85, 21.91–28.01, 10.76–20.27, 20.59–24.77, 18.96–23.14, and 20.75–21.15 %, respectively) as compared to continuous ponding or farmer practice, where the As accumulation in root: 13.43–17.20 mg/kg; stem: 8.64–10.36 mg/kg; leaves: 2.91–3.44 mg/kg; flag leaf: 0.68–1.09 mg/kg; husk: 1.88–2.11 mg/kg; and grain: 0.52–0.67 mg/kg. However, aerobic rice and saturation of top soil recorded significantly higher grain yield at diara land (7,104–7,141 kg/ha) and only in saturation of top soil at medium land topo sequence (6,654–6,717 kg/ha). The correlation study showed the positive correlation in between grain As and root, straw, husk As, grain Zn, and grain Fe (R ² = 0.893–0.976, p > 0.01), but the negative correlation with the grain P, soil P, soil Fe, and soil Zn (R ² = 0.633–0.841, p > 0.01). About 3.904–6.063 kg/ha of As was added on the surface soil by the contaminated groundwater and most of the added As was accumulated and remained on the top soil (0–30 cm).     

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.     

Localization,validation and characterization of plant-type QTLs on chromosomes 4 and 6 in rice (Oryza sativa L.)

Improvement of rice (Oryza sativa L.) plant type is a major breeding objective. This study aimed to precisely localize and characterize key genomic regions for plant type using near-isogenic individuals. Selfing of partially heterozygous F₅ recombinant inbred (RI) individuals [parental varieties Milyang 23 (M23) and Akihikari (AK)] developed heterogeneous inbred families (HIFs) composed of 108 and 93 F₇ progenies, which segregated at molecular marker loci on the long arms of chromosomes 4 and 6, respectively. The progeny lines (F₈) were evaluated for traits composing plant type in Los Baños, Philippines, to locate quantitative trait loci (QTLs) using interval mapping and to evaluate the effects of the QTL region by phenotypic comparison between the genotypes. QTLs for the traits were detected in 17 cM across XNpb12 on chromosome 6. The M23 homozygote for the QTL region resulted in a >7% increase and decrease in plant length and tiller number at heading, respectively, relative to the AK homozygote. Consequently, culm length (CL) and traits determining flag-leaf and panicle sizes increased 5–56% by the M23 homozygote, together with a 15% decrease in panicle number. For a QTL region detected in 6 cM across XNpb235 on chromosome 4, the AK homozygote had similar effects on these traits, except CL. The directions and magnitudes of their effects agreed with those previously estimated in the RI line population, thus increasing confidence in primary QTL analyses for plant type. Analyzing the HIFs validated and characterized the two QTL regions greatly involved in determining varietal plant type from an early growth stage to maturity, providing information useful for empirical and marker-assisted breeding towards rice improvement.     

Relationship of growth parameters and nutrients uptake with canola (Brassica napus L.) yield and yield contribution at different nutrients availability

A field experiment was conducted to evaluate the effect of different nutrients on canola (Brassica napus L.) growth parameters, nutrient uptake and ultimately on seed yield. For this purpose a split plot experimental design, with 10 treatments in 4 replications was carried out in 2004-2005, in silt-clay soil at Baiecola Agricultural Research Station, Mazandaran Iran. Canola seed yield, growth parameters (CGR, LAI, RGR and NAR), dry matter accumulation and HI and nutrient content of the leaf were examined. NPK fertilizers together with S and Zn, singly or in combination were applied. The results showed that at treatments T5 (NP), T8 (NPK), T9 (NPKS) and T10 (NPKZn) the higher seed yield (> 2600 kg ha(-1)) coincided with TDM > 880 g m(-2) the peak CGR > or = 13.9 g m(-2) day(-1) and the maximum LAI > or = 4.1. The higher seed yield at T5, T8, T9 and T10 coincided with higher concentrations of nutrients: N, P, K, S and Zn in leaf at flowering having > or = 3.40%, > or = 0.25%, > or = 1.53%, > or = 110 ppm and > or = 22.7 ppm, indicating substantial levels of translocation of nutrients at various stages of plant growth and higher number of pods per plant (> or = 179). Combined application of NPKZn at T10 resulted in maximum seed yield (3090 kg ha(-1)), coinciding with the maximum number of pods per plant (230), maximum TDM (1043 kg ha(-1)), maximum CGR (20.09 g m(-2) day(-1)) and maximum LAI (4.69).     

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.     

Isolation of a novel mutant gene for soil-surface rooting in rice (Oryza sativa L.)

Background

Root system architecture is an important trait affecting the uptake of nutrients and water by crops. Shallower root systems preferentially take up nutrients from the topsoil and help avoid unfavorable environments in deeper soil layers. We have found a soil-surface rooting mutant from an M₂ population that was regenerated from seed calli of a japonica rice cultivar, Nipponbare. In this study, we examined the genetic and physiological characteristics of this mutant.

Results

The primary roots of the mutant showed no gravitropic response from the seedling stage on, whereas the gravitropic response of the shoots was normal. Segregation analyses by using an F₂ population derived from a cross between the soil-surface rooting mutant and wild-type Nipponbare indicated that the trait was controlled by a single recessive gene, designated as sor1. Fine mapping by using an F₂ population derived from a cross between the mutant and an indica rice cultivar, Kasalath, revealed that sor1 was located within a 136-kb region between the simple sequence repeat markers RM16254 and 2935-6 on the terminal region of the short arm of chromosome 4, where 13 putative open reading frames (ORFs) were found. We sequenced these ORFs and detected a 33-bp deletion in one of them, Os04g0101800. Transgenic plants of the mutant transformed with the genomic fragment carrying the Os04g0101800 sequence from Nipponbare showed normal gravitropic responses and no soil-surface rooting.

Conclusion

These results suggest that sor1, a rice mutant causing soil-surface rooting and altered root gravitropic response, is allelic to Os04g0101800, and that a 33-bp deletion in the coding region of this gene causes the mutant phenotypes.