Indica Hybrid Research Articles

Rapid Construction of a High-Density Rice Linkage Map by High Efficiency Genome Scanning (HEGS) System

High-density linkage maps are essential tools for genome analysis of various biological traits. Our developed compact multi-gel system, HEGS (high efficiency genome scanning) is a high-throughput and high-cost-performance electrophoresis apparatus. Using this system, a high-density (average interval 2.3 cM) map with 1 065 AFLP and 63 SSR markers was constructed from recombinant inbred lines of a japonica and indica hybrid in just two months of electrophoreses by a single person. More than 50% of the mapped AFLP markers were commonly polymorphic for several combinations between japonica and indica rice and 15% were applicable for genetically closer crosses between upland and lowland types of japonica rice. This system can be used for rapid analyses of all kinds of markers.

Effect of Low Temperature Pre-Treatment on Anther Culture in Selected Indica, Japonica Rice Varieties and their Inter Sub-Specific Hybrids

Effect of cold pre-treatment of panicles with reduced temperatures (of 5°C, 7°C, 8°C and 10°C) and exposure for different time durations (at weekly intervals up to 4 weeks) on anther culture of Japonica rice variety Hu lo tao, Indica rice varieties Bg 90-2, Bg 379-2 and their F1 hybrids for high frequency callus induction and plant regeneration was investigated. Anthers were cultured in N6 medium with 5% sucrose, 2 mg l-1 2,4 D and 0.5 mg l-1 Kinetin. The cultures were kept in the dark at 28 ± 2°C for callus induction. Induced calli of 1-2 mm diameter were transferred to half strength Murashige and Skoog (MS) medium supplemented with 2.0 mg l-1 Kinetin and 0.5 mg l-1 NAA. The effect of variety and cold pre-treatment was significant at 5% probability level. The Indica varieties had the lowest callus induction frequency (0.3% - 7.0%). Japonica and Japonica × Indica hybrids had high callus induction (12.3% - 70.0%). The F1 hybrid Hu lo tao × Bg 90-2 had comparatively high callus induction (31.0% - 70.0%) than the other genotypes. Japonica variety Hu lo tao and F1 hybrids had highest callus development at cold pre-treatment at 8°C for 14 and 21 days. The highest green plant regeneration was observed in F1 hybrid, Hu lo tao × Bg 90-2 followed by Japonica variety subjected to 8°C for 14 days. Very poor green plant regeneration was observed in Indica variety, Bg 90-2 when it was exposed to 7°C for 21 and 28 days. Variety Bg 379-2 did not produce any green plant at any treatment. The F1 hybrid Hu lo tao × Bg 379-2 produced lower green plants than F1 hybrid Hu lo tao × Bg 90-2. Cold pre treatment at 8°C temperature for 14 days was found to be most effective for anther culture in experimental genotypes used in the study. Key words: variety, cold pre-treatment, callus induction, plant regeneration, rice DOI: 10.4038/cjsbs.v38i1.1322 Cey. J. Sci. (Bio. Sci.) 38 (1): 11-16, 2009

Quality characteristics and field performance of selectable marker-free transgenic rice with antisense Wx gene and improved quality derived from the elite parents of hybrid indica rice

In rice grains, high amylose content (AC) is correlated with poor grain quality, particularly in indica hybrid rice. To obtain indica hybrid rice with improved cooking and eating qualities, we introduced the antisense Waxy ( Wx) gene into 2 elite parental lines of indica hybrid rice by using co-transformation methods. Subsequently, we selected several elite homozygous transgenic lines that did not contain the selectable marker. The expression of the endogenous Wx gene of the selected transgenic lines was significantly downregulated, resulting in low AC in the mature seeds; moreover, the AC in some lines reduced to the level observed in glutinous rice. With the decrease in AC, the gel consistency of the transgenic rice became softer, and the gelatinization temperature tended to be higher than those of the wild types, especially in the case of the Longtefu-derived transformants. We also analyzed the pasting properties of the selected transgenic low-AC lines, and we noted an improvement in the pasting properties of the transgenic rice lines. The results from a field trial indicated that the grain weights of the transgenic lines with lower AC exhibit remarkable reduction compared with those of the wild types.

Evaluation of a Sib-mated Population of Buddleja davidii ‘White Bouquet’ × Buddleja indica Hybrids

Abstract A hybridization experiment to sib-cross a population of B. davidii Franch. ‘White Bouquet’ × B. indica Lam. hybrids was initiated in 2004 to generate a larger population of such hybrids to assess landscape potential. Large populations from the sib-mated B. davidii ‘White Bouquet’ × B. indica hybrids can be generated. The population was initially assessed for growth habit, leaf size, floriferousness, seed morphology, and winter hardiness. Susceptibility to spider mite damage was also noted in the population. Although these hybrids have desirable traits such as non-dehiscent fruit and ornamental foliage, further hybridization is needed to address undesirable traits such as sparse growth and flowering along with spider mite susceptibility.

Developmental Genetics Analysis for Plant Height in indica Hybrid Rice Across Environments

The developmental genetics of plant height was analyzed from two groups of three-line indica hybrid rice at two environmental conditions based on the NCII design, using the additive-dominant developmental genetics models and the statistic methods. The results showed that the rice genotypes and environmental conditions could both affect plant height, and the effects of environment on plant height decreased gradually with plant development. Additive and dominant effects both governed the performance of plant height at all developmental stages. However, the degrees of effect varied among the rice genotypes. Moreover, the interaction between environments and genotypes also affected plant height. The genetic effects differed at most developmental stages. Furthermore, the expression of additive effect was more active than that of dominant effect. Conditional interaction effects with environment also influenced plant height during genetic development, especially at the early stage. Mid-parent heterosis ( H MP) increased gradually with the developmental stage of plant height, and maximized at the latest stage, whereas the heterosis over the better parent ( H BP) showed small differences among the genotypes, and kept stable at the later stage, with positive numeric value. At most developmental stages, conditional H MP was positively significant, while conditional H BP was negatively significant. All above results suggest that H MP and H BP have some new expressions in all developmental periods and the levels and directions are quite different.

Effects of Chalkiness on Cooking, Eating and Nutritional Qualities of Rice in Two indica Varieties

An experiment was conducted to investigate the effects of chalkiness on cooking, eating and nutrition qualities of rice using Gangyou 527 (indica hybrid rice) and Zhaiyeqing 8 (conventional indica rice) as materials. Compared with the milled rice without chalkiness, amylose content, final viscosity, setback and consistence increased significantly, while gel consistence, peak viscosity and breakdown decreased remarkably and other RVA values did not have significant changes in the chalky rice of Gangyou 527. The differences in the above indices between the chalky and non-chalky rice was not remarkable in Zhaiyeqing 8. The crude protein content of chalky rice in Zhaiyeqing 8 was significantly lower than that of non-chalky rice, but there was no remarkable change between the chalky and non-chalky rice in Gangyou 527. Glutelin content fell significantly, and albumin, globulin, prolamine and lysine contents did not change significantly in chalky rice compared with non-chalky rice in the two varieties.

Genetics and Improvement of Bacterial Blight Resistance of Hybrid Rice in China

Since 1980s, rice breeding for resistance to bacterial blight has been rapidly progressing in China. The gene Xa4 was mainly used in three-line indica hybrid and two-line hybrid rice. The disease has been ‘quiet’ for 20 years in China, yet in recent years it has gradually emerged and been prevalent in fields planted with newly released rice varieties in the Changjiang River valley. Under the circumstances, scientists inevitably raised several questions: what causes the resurgence and what should we do next? And/or is resistance breeding still one of the main objectives in rice improvement? Which approach do we take on resistance breeding so that the resistance will be more durable, and the resistance gene will be used more efficiently? A combined strategy involving traditional method, molecular marker-assisted selection, and transgenic technology should bring a new era to the bacterial blight resistance hybrid rice breeding program. This review also briefly discusses and deliberates on issues related to the broadening of bacterial blight resistance, and suitable utilization of resistance genes, alternate planting of available resistance genes; and understands the virulent populations of the bacterial pathogen in China even in Asia.

Yield and photosynthetic characteristics of flag leaves in Chinese rice ( Oryza sativa L.) varieties subjected to free-air release of ozone

The effects of elevated O 3 concentration ([O 3]) on grain yield and photosynthetic characteristics of flag leaves in rice ( Oryza sativa L.) were studied using a hybrid indica cultivar SY63 and a conventional Japonica cultivar WYJ3. Both cultivars were grown in the field under ambient (A-O 3) and elevated [O 3] (E-O 3, ambient × 1.5) using free-air O 3 enrichment in Jiangdu city, Jiangsu province, China. The E-O 3 significantly reduced above-ground biomass ( p = 0.047) and grain yield ( p = 0.0046), but had no significant effect on harvest index ( p = 0.18) across cultivars. The hybrid Indica cultivar SY63 was more sensitive to E-O 3 than the conventional Japonica cultivar WYJ3. The above-ground biomass was reduced by 17.6% for SY63 and 6.6% for WYJ3, whereas the grain yield was reduced by 20.7% for SY63 and 6.3% for WYJ3. A barely non-significant ( p = 0.079) interaction between O 3 and cultivar on grain yield suggested a higher sensitivity of the hybrid variety: SY63. In SY63, flag leaves exhibited an earlier and stronger response in photosynthetic characteristics to E-O 3. Depression in light-saturated photosynthetic rate ( A sat) was first observed at 237 day of year (DOY) in SY63, and the seasonal mean A sat was reduced by 23.1%. In contrast, for WYJ3, the conventional cultivar, the impact of E-O 3 on A sat was negligible until 266 DOY, and seasonal mean decrease of A sat was only 9.4%. The same trend was found in chlorophyll a fluorescence parameters. In SY63, actual quantum yield of PSII ( p = 0.007) and q p (photochemical quenching) ( p = 0.002) were significantly decreased at 248 DOY and the downward trends persisted throughout the rest of the life span of flag leaves. No such changes were observed in WYJ3. In the ozonated flag leaves of SY63, necrotic damages occurred and chlorophyll contents declined significantly by 12.6–43.6% through the entire functional duration of the leaf. As for WYJ3, chlorophyll remained unaffected until a 25.7% decrease appeared at 278 DOY under E-O 3. The observed yield losses were compared with those estimated from two existing exposure–yield loss relationships for rice. The yield loss in SY63 was much greater than either estimate, whereas that in WYJ3 was comparable to one estimate but was moderately larger than the other. This warrants further studies with a much larger number of varieties. Open-air O 3 release would serve as the best platform for such a large-scale screening of rice varieties to increasing [O 3].

Morphological and physiological traits of roots and their relationships with shoot growth in “super” rice

Success in “super” rice breeding has been considered a great progress in rice production in China. This study aimed to test the hypothesis that an improved root system may contribute to better shoot growth and consequently to higher grain yield in “super” rice. Two “super” rice varieties Liangyoupeijiu (an indica hybrid) and Huaidao 9 (a japonica inbred) and two elite check varieties Yangdao 6 (an indica inbred) and Yangfujiang 8 (a japonica inbred) were field-grown at Yangzhou, China in 2006 and 2007. Root and shoot dry weight (DW) was significantly greater in “super” rice varieties than in check ones throughout the growth season in both years, so was the root length density. Root oxidation activity (ROA) and root zeatin (Z) zeatin riboside (ZR) content, in per plant basis, were significantly greater in “super” rice than check varieties before and at heading time. However, both ROA and root Z + ZR content, either in per plant basis or per unit root DW basis, were significantly lower in ‘super’ rice than in check varieties at the mid- and late grain filling stages. Grain yield of the two ‘super’ rice varieties, on average, was 10.2 t ha −1 in 2006 and 11.4 t ha −1 in 2007, and was 13% and 21% higher than that of check varieties, respectively. The high grain yield was mainly due to a larger sink size (total number of spikelets) as a result of a larger panicle. The percentage of filled grains of the two “super” rice varieties, on average, was 72.9% in 2006 and 79.0% in 2007, and was 19.4% and 12.9%, respectively, lower than that of the check varieties. The mean ROA and root Z + ZR content during the grain filling period significantly correlated with the percentage of filled grains. Collectively, the data suggest that an improved root and shoot growth, as showing a larger root and shoot biomass and greater root length density during the whole growing season and higher ROA and root Z + ZR content per plant at early and mid-growth stages, contributes to the large sink size and high grain yield in the “super” rice varieties. The data also suggest the yield of “super” rice varieties can be further increased by an increase in filled grains through enhancing root activity during grain filling.

Light-saturated photosynthetic rate in high-nitrogen rice (Oryza sativa L.) leaves is related to chloroplastic CO2 concentration

To identify the effect of nitrogen (N) nutrition on photosynthetic efficiency and mesophyll conductance of rice seedlings (Oryza sativa L., cv. 'Shanyou 63' hybrid indica China), hydroponic experiments with different concentrations of N were conducted in a greenhouse. Although leaf N concentration on a dry mass basis increased with increasing supply of N, no significant differences in seedling biomass were observed. A higher light-saturated CO(2) assimilation rate (A) with a high concentration of supplied N was associated with a higher carboxylation efficiency (CE), but not a higher apparent quantum yield (alpha). Based on classic photosynthetic models, both the Rubisco content and the ribulose bisphosphate (RuBP) regeneration rate were sufficient for light-saturated photosynthesis in rice seedlings; the estimated chloroplastic CO(2) concentration (C(c)) and mesophyll conductance (g(m)) demonstrated that a low C(c) was the ultimate limiting factor to photosynthetic efficiency with a higher N supply. Due to a greater chloroplast size (i.e. a shorter distance to the plasma membrane) with a higher supply of N, the CO(2) transport resistance in the liquid phase (g(liq)) in high-N leaves was lower than that in low-N leaves, which resulted in higher g(m) and C(c) in high-N leaves. Although CE(A/Ci) was higher with a high supply of N, there were no differences in CE(A/Cc) between plants grown with different concentrations of N, indicating that the carboxylation capacity of Rubisco between plants grown at different N concentrations was constant. The enhanced photosynthetic rate with supply of a high N concentration was attributed to a higher CO(2) concentration in the chloroplasts, related to a higher mesophyll conductance due to an increased chloroplast size.

Population quality and grain yield construction of mid-season indica hybrid rice “Wandao153” under different N applications

以超高产中籼杂交水稻“皖稻153”为材料, 在大田条件下,比较了不同施氮量对杂交中籼水稻群体质量、氮肥利用和产量形成的影响。结果表明,150 kg(N)·hm^-2、187.5 kg(N)·hm^-2、225.0 kg(N)·hm^-2、262.5 kg(N)·hm^-2和300.0 kg(N)·hm^-2等5种施氮量下杂交中籼稻产量差异显著, 在150～262.5 kg(N)·hm^-2范围内,产量随施氮量增加而增加,以262.5 kg·hm^-2施氮处理的产量最高(11 355 kg·hm^-2),施氮量增加到300.0 kg(N)·hm^-2产量下降。不同施氮处理间产量差异主要是因为群体颖花量的差异,施氮量与群体颖花量呈极显著正相关(<i>r</i>=0.963 5^**)。施氮量明显影响群体质量,适宜施氮量(262.5 kg·hm^-2)能保证杂交中籼水稻达到较高的叶面积指数(LAI)和粒叶比,在抽穗期维持较高的叶片干物质分配比例和单茎叶片重,有利于后期植株光合能力的提高和光合产物的积累,使后期物质积累的贡献率提高，从而增加产量。适宜施氮量(262.5 kg·hm^-2)的氮肥农学利用率也最高。推荐江淮稻区杂交中籼稻超高产栽培的适宜施氮量为 262.5 kg·hm^-2

Correlation Between Parents and F 1 and Combining Ability of Parents on Seed Dormancy in indica Rice ( Oryza sativa)

Dormancy indices of hulled and dehulled seeds were investigated by using 19 cytoplasmic male sterile (CMS) lines, 9 restorer lines and their 109 F 1 hybrids of indica hybrid rice. The seeds of each F 1 and the parents were harvested on 35 days after flowering. Combining ability was analyzed in 25 combinations made by 5 CMS lines and 5 restorer lines (North Carolina II mating design). The seed dormancy index of F 1 was positively and highly significantly correlated with those of their parents and mid-parent value. Out of the 109 combinations, 82 combinations showed mid-parent heterosis, and 43 heterobeltiosis. Seed dormancy indices of F 1s and their parents declined dramatically in dehulled seeds compared with hulled seeds, indicating that the hull played an important role in seed dormancy. However, the trends were similar in hulled seeds and dehulled seeds in terms of relationships between the seed dormancy indicices in F 1 and their parents. The influence of hull on seed dormancy mainly depended on F 1 genotype, not on the hull from maternal parent. The variances of general combining ability (GCA) in female and male parents occupied 59.2% and 31.1% of total variance, respectively. The variance of specific combining ability (SCA) in combinations occupied 9.7% of total variance, indicating that gene additive effects were principal. Among the 5 CMS lines, II112A had the highest GCA effect for seed dormancy, followed by D62A. Among the 5 restorer lines, IR112 had the highest GCA effect for seed dormancy, followed by 2786. These lines are elite parental materials for breeding F 1 hybrid rice with stronger seed dormancy.

Comparisons in Agronomic and Physiological Traits of Rice Genotypes Differing in Cadmium-Tolerance

Cadmium (Cd) is one of major contaminants in agricultural soil, threatening agricultural production and human health. To understand agronomic and physiological characteristics of rice genotypes differing in Cd-tolerance would have great signifi-cance in selecting or breeding a Cd-tolerant cultivar. In this study, two Cd-tolerant rice genotypes of Shanyou 63 (indica hybrid) and Yangjing 9538 (japonica) and two Cd-susceptible genotypes of Yangdao 6 (indica) and Wuyunjing 7 (japonica) were pot-grown at a farm of Yangzhou University, Yangzhou, Jiangsu Province in 2004 and 2005. 150 mg kg-1 Cd was added into pot soil before seedling transplanting (Cd treatment), and no Cd addition was taken as control (CK). Under the Cd treatment, the grain yield was reduced by 6.2–8.9% for the Cd-tolerant genotypes and by 38.3–47.1% for the Cd-susceptible ones when compared with their respective CKs. The reduction in grain yield was mainly attributed to the reductions of panicles per pot and spikelets per panicle. The differences in seed-setting rate and 1 000-grain weight were not significant between the Cd treatment and CK. The Cd treatment markedly inhibited the tillering of the Cd-susceptible genotypes, resulting in the reduction in dry matter accumula-tion during the whole growth period. Cd little affected the translocation of non-structural carbohydrate from culms and sheaths and harvest index. For Cd-susceptible genotypes, the Cd treatment significantly reduced root oxidation activity and photosynthetic rate, activities of superoxide dismutase and catalase of leaves, and obviously increased contents of superoxidate radical and hy-drogen peroxide and ethylene evolution rate of leaves, and the concentration of 1-aminocylopropane-1-carboxylic acid in root bleedings from the tillering to jointing stages, while the Cd treatment much less affected the above physiological traits for the Cd-tolerant genotypes. The differences in the above traits at heading and afterwards and abscisic acid content in leaves during the whole growth period were not significant between the Cd treatment and CK. The results indicate that the effects of Cd on ricegrowth and development are mainly during the early growth period (from tillering to jointing), and more tillers, stronger root ac-tivity and antioxidative defense system, and less ethylene synthesis in the plants during this period would be considered as agro-nomic and physiological traits of Cd-tolerant genotypes of rice.

Effects of different Nitrogen forms and osmotic stress on water use efficiency of rice (Oryza sativa)

AbstractA hydroponic experiment with simulated water stress induced by polyethylene glycol (PEG) was conducted in greenhouse to study the effects of different nitrogen (N) forms (; and the mixture of and ) on water stress tolerance and water use efficiency (WUE and WUET) of different rice cultivars. Two rice cultivars (cv. ‘Shanyou 63’ hybrid indica and ‘Yangdao 6’ indica, China) were grown under non‐water‐ or water‐stressed condition [10% (w/v) PEG, molecular weight 6000] with different N forms for 3 weeks. Under non‐water stress, the biomass of Shanyou 63 was 50.0% and 64.3% and of Yangdao 6 was 6.9% and 87.8% higher under the supply of mixture of and than either under the sole supply of or , respectively; under water stress, the biomass of both rice cultivars decreased in all three nitrogen forms compared with non‐water stress; however, the inhibitory effect of water stress on biomass varied between and nutrition; the reduction of dry matter was significantly higher in than in nutrition. Compared with non‐water stress, under water stressed condition, WUE of both two rice cultivars significantly decreased in supply; WUE did not vary in and the mixture supply. It is concluded that (a) the resistance of water stress of rice seedlings is related to nitrogen form; (b) under water stress, could maintain a higher WUE compared with ; (c) hybrid indica rice seedlings have a higher water stress tolerance than indica rice seedlings.

Analysis on Dry Matter Production Characteristics of Super Hybrid Rice

Six middle-season indica hybrid rice combinations, including five super hybrid rice combinations with the high yield about 10.5 t/ha and a check hybrid rice combination Shanyou 63 with a yield potential about 9.5 t/ha, were used as materials to study the dry matter production characteristics. The super hybrid rice showed a high ability in dry matter production and accumulation and its yield enhanced with the increase of dry matter accumulation. The advantage period of dry matter production in the super hybrid rice was mainly at the middle and late growth stages compared with the check. The grain yield had no significant correlation with the dry matter accumulation before the elongation stage while had a significantly positive correlation with the dry matter accumulation from the elongation to maturity stages in super hybrid rice. There were more dry matter in vegetative organs at the heading stage in the super hybrid rice but its contribution to yield (apparent conversion percentage) was averagely 4.3 percent points lower than that in the check. For crop growth rate (CGR), the comparative advantage of super hybrid rice was at the middle and late stages, especially after flowering. Moreover, as the rising of leaf area index (LAI) and leaf area duration (LAD), CGR enhanced. The total LAD and the mean of LAD per day of super hybrid rice was about 14.79% and 10.31% higher than those of the check, respectively. The results indicate that the high yield of super hybrid rice mostly comes from the products of photosynthesis after heading, which is shown by the increased CGR at middle and later stages. It is suggested that LAD character might be used to better explain the advantage in the dry matter production of super hybrid rice than LAI.

Yield formation of CO 2-enriched hybrid rice cultivar Shanyou 63 under fully open-air field conditions

Hybrid indica rice ( Oryza sativa L.) cultivars play an important role in rice production system due to its heterosis, resistance to environmental stress, large panicle and high yield potential. However, no attention has been given to its yield responses to rising atmospheric [CO 2] in conjunction with nitrogen (N) availability. Therefore we conducted a free air CO 2 enrichment (FACE) experiment at Yangzhou, Jiangsu, China (119°42′0′′E, 32°35′5′′N), in 2004–2006. A three-line hybrid indica rice cv. Shanyou 63 was grown at ambient and elevated (ca. 570 μmol mol −1) [CO 2] under two levels of supplemental N (12.5 g Nm −2 and 25 g Nm −2). Elevated [CO 2] had no effect on phenology, but substantially enhanced grain yield (+34%). The magnitude of yield response to [CO 2] was independent of N fertilization, but varied among different years. On average, elevated [CO 2] increased the panicle number per square meter by 10%, due to an increase in maximum tiller number under enrich [CO 2], while productive tiller ratio remained unaffected. Spikelet number per panicle also showed an average increase of 10% due to elevated [CO 2], which was supported by increased plant height and stem dry weight per tiller. Meanwhile, elevated [CO 2] caused a significant enhancement in both filled spikelet percentage (+5%) and individual grain weight (+4%). Compared with the two prior FACE studies on rice, hybrid indica rice cultivar appears to profit much more from elevated [CO 2] than japonica rice cultivar (ca. +13%), not only due to its stronger sink generation, but also enhanced capacity to utilize the carbon sources in a high [CO 2] environment. The above data has significant implication with respect to N strategies and cultivar selection under projected future [CO 2] levels.

Comparison of Agronomic and Physiological Traits of Rice Genotypes Differing in Cadmium-Tolerance

Cadmium (Cd) is one of major contaminants in agricultural soil, threatening agricultural production and human health. To understand agronomic and physiological characteristics of rice ( Oryza sativa L.), genotypes differing in Cd-tolerance, 2 Cd-tolerant rice genotypes Shanyou 63 ( indica hybrid) and Yangjing 9538 ( japonica)and 2 Cd-susceptible genotypes Yangdao 6 ( indica) and Wuyunjing 7 ( japonica) were pot-grown in 2004 and 2005. In the Cd treatment, 150 mg kg −1 Cd was added into pot soil before seedling transplanting, and no Cd addition was taken as control. Under the Cd treatment, the grain yield was reduced by 6.2–8.9% for the Cd-tolerant genotypes and by 38.3–47.1% for the Cd-susceptible ones compared with their respective controls. The reduction in grain yield was mainly attributed to the reduction of panicles per pot and spikelets per panicle. The differences in seed-setting rate and 1000-grain weight were not significant between the Cd treatment and the control. The Cd treatment markedly inhibited the tillering of the Cd-susceptible genotypes, resulting in the reduction of dry matter accumulation during the whole growth period. Cd slightly affected the translocation of nonstructural carbohydrate from culms and sheaths, as well as harvest index. For Cd-susceptible genotypes from the tillering to the jointing stages, the Cd treatment significantly reduced root oxidation activity and photosynthetic rate, activities of superoxide dismutase, and the catalase in leaves, but obviously increased the content of the superoxidate radical, hydrogen peroxide, and ethylene evolution rate of leaves, as well as the concentration of 1-aminocylopropane-1-carboxylic acid in root bleedings. After the heading stage, the Cd treatment affected the above-mentioned physiological traits of the Cd-tolerant genotypes much less. The differences in the above-mentioned traits at heading and later, as also the abscisic acid content in leaves during the whole growth period were not significant between the Cd treatment and the control. The results indicated that the effects of Cd on rice growth and development were mainly during the early growth period (from tillering to jointing). More tillers, stronger root activity, and antioxidative defense system, and less ethylene synthesis in the plants during this period were considered as the agronomic and physiological traits of Cd-tolerant genotypes of rice.

Yield, grain quality and water use efficiency of rice under non-flooded mulching cultivation

Plastic film or straw mulching cultivation under non-flooded condition has been considered as a new water-saving technique in rice production. This study aimed to investigate the yield performance in terms of quality and quantity and water use efficiency (WUE) under such practices. A field experiment across 3 years was conducted with two high-yielding rice cultivars, Zhendao 88 (a japonica cultivar) and Shanyou 63 (an indica hybrid cultivar) and four cultivation treatments imposed from transplanting to maturity: traditional flooding as control (TF), non-flooded plastic film mulching (PM), non-flooded wheat straw mulching (SM), and non-flooded no mulching (NM). Compared with those under the TF, root oxidation activity, photosynthetic rate, and activities of key enzymes in sucrose-to-starch conversion in grains during the grain filling period were significantly increased under the SM, whereas they were significantly reduced under the PM and NM treatments. Grain yield showed some reduction under all the non-flooded cultivations but differed largely among the treatments. The reduction in yield was 7.3–17.5% under the PM, 2.8–6.3% under the SM, and 39–49% under the NM. The difference in grain yield was not significant between TF and SM treatments. WUE for irrigation was increased by 314–367% under the PM, 307–321% under the SM, and 98–138% under the NM. Under the same treatment especially under non-flooded conditions, the indica hybrid cultivar showed a higher grain yield and higher WUE than the japonica cultivar. The SM significantly improved milling, appearance, and cooking qualities, whereas the PM or the NM decreased these qualities. We conclude that both PM and SM could significantly increase WUE, while the SM could also maintain a high grain yield and improve quality of rice. The SM would be a better practice than the PM in areas where water is scarce while temperature is favorable to rice growth, such as in Southeast China.

Effect of High Temperature at Meiosis Stage on Seed-Setting Rate in Rice

High temperature, especially at flowering stage and meiosis stage, causes sterility of florets and yield reduction in rice ( Oryza sativa L.). To evaluate the effect of high temperature on rice yield quantitatively, 2 rice cultivars, Huajing 1 ( japonica) and Teyou 559 ( indica hybrid) were treated with ladder temperatures (31, 33, 35, 37, 39, and 41°C) for 1, 3, and 5 d at meiosis stage in Artificial Climate incubators. The high temperature stress was conducted for 5 h (8:40–13:30) at each treatment day. The natural temperature treatment was set as the control. The seed-setting rates of both cultivars were slightly affected ( P > 0.05) when temperature was lower than 33°C. But with the increase of temperature and its duration, seed-setting rate decreased gradually. The relationship between daily relative seed-setting rate (RSS) and temperature was fitting with a quadratic equation. The total effect of high temperature at meiosis stage on RSS was described with the products of daily RSS.

Mechanisms of Enhanced Rice Growth and Nitrogen Uptake by Nitrate

Rice is being increasingly cultivated in intermittently irrigated regions and also in aerobic soil in which Nitrate (NO − 3) plays important role in nutrition of plant. However, there is no information regarding the influence of nitrate on the overall growth and uptake of nitrogen (N) in rice plant. Solution culture experiments were carried out to study the effects of NO − 3 on the plant growth, uptake of N, and uptake kinetics of NH + 4 in four typical rice ( Oryza sativa L.) cultivars (conventional indica, conventional japonica, hybrid indica, and hybrid japonica), and on plasma membrane potential in roots of two conventional rice cultivars ( indica and japonica) at the seedling stage. The results obtained indicated that a ratio of 50/50 NH + 4 -N/NO − 3-N increased the average biomass of rice shoots and roots by 20% when compared with that of 100/0 NH + 4 -N/NO − 3-N. In case of the 50/50 ratio, as compared with the 100/0 ratio, total N accumulated in shoots and roots of rice increased on an average by 42% and 57%, respectively. Conventional indica responds to NO − 3more than any other cultivars that were tested. The NO − 3supply increased the maximum uptake rate ( V max) of NH + 4 by rice but did not show any effect on the apparent Michaelis-Menten constant ( K m) value, with the average value of V max for NH + 4 among the four cultivars being increased by 31.5% in comparison with those in the absence of NO − 3. This suggested that NO − 3 significantly increased the numbers of the ammonium transporters. However, the lack of effect on the K m value also suggested that the presence of NO − 3had no effect on the affnity of the transporters for NH + 4. The plasma membrane potential in the roots of conventional indica and japonica were greatly increased by the addition of NO − 3, suggesting that NO − 3could improve the uptake of N by roots of the rice plant. In conclusion, the mechanisms by which NO − 3enhances the growth and N uptake of rice plant was found by the increased value of V max of NH + 4 and increased plasma membrane potential. Thus promotion of nitrification in paddy soil is of great significance for improving the production of rice.