Variation of Cd concentration in various rice cultivars and derivation of cadmium toxicity thresholds for paddy soil by species-sensitivity distribution

It is imperative to derive an appropriate cadmium (Cd) health risk toxicity threshold for paddy soils to ensure the Cd con-centration of rice grains meet the food safety standard. In this study, 20 rice cultivars from the main rice producing areas in China were selected, and a pot-experiment was conducted to investigate transformation of Cd in paddy soil-rice system with 0 (CK), 0.3 mg kg–1 (T1) and 0.6 mg kg–1 (T2) Cd treatments in greenhouse. The results showed that Cd concentrations of rice grains existed signiifcant difference (P<0.05) in 20 rice cultivars under the same Cd level in soil. The Cd concentrations of rice grains of the CK, T1 and T2 treatments were in the range of 0.143–0.202, 0.128–0.458 and 0.332–0.806 mg kg–1, respectively. Marked differences of the ratios of Cd concentration for soil to rice grain (BCFs) and transfer factors (TFs, root to grain and straw to grain) among the tested cultivars were observed in this study. The bioconcentration factors (BCFgrain) and TFs of the 20 rice cultivars were 0.300–1.112 and 0.342–0.817, respectively. The TFs of Cd from straw to grain ranged from 0.366 to 1.71, with signiifcant differences among these 20 rice cultivars. The bioconcentration factors (BCFgrain) and TFs among the 20 rice cultivars ranged from 0.300–1.112 and 0.342–0.817, respectively. The species-sensitivity distribu-tion (SSD) of Cd sensitivity of the rice species could be iftted wel with Burr-III (R2=0.987) based on the data of BCFs. The toxicity threshold of Cd derived from SSD for the paddy soil was 0.507 mg kg–1 in the present study.

Difference in Selenium Accumulation in Shoots of Two Rice Cultivars

Two japonica rice （Oryza sativa L.） cultivars, Xiushui 48 and S. Andrea, differing in their ability to accumulate Se in the grain （as high as a three-fold difference）, were compared for selenium （Se） accumulation in their shoots when their growth media was supplied with different forms of Se. Results indicated that when treated with 0.25μmol L^-1 Na2SeO3, Xiushui 48 accumulation of Se in the shoots was significantly more rapid （P〈0.05） than S. Andrea, probably because of greater Se uptake and transport in Xiushui 48. Xiushui 48 rice seedlings had a higher shoot-Se accumulation rate and absorbed selenocysteine （Se-Cys） more rapidly than S. Andrea seedlings. However, when treated with Se as 0.25μmol L^-1 selenomethionine （Se-Met）, the S. Andrea seedlings＇ accumulation rate was significantly greater （P〈0.05） than that of Xiushui 48. Possibly, the high Se accumulation rate of Xiushui 48 seedling shoots compared to S. Andrea shoots was the result of a higher capacity of Xiushui 48 to transform selenite to organic Se compounds and a higher selenite uptake rate.

Agronomic performance of drought-resistance rice cultivars grown under alternate wetting and drying irrigation management in southeast China

Compared to drought-susceptible rice cultivars(DSRs),drought-resistance rice cultivars(DRRs)could drastically reduce the amount of irrigation water input and simultaneously result in higher grain yield under water-saving irrigation conditions.However,the mechanisms underlying these properties are unclear.We investigated how improved agronomic traits contribute to higher yield and higher water use efficiency(WUE)in DRRs than in DSRs under alternate wetting and drying(AWD).Two DRRs and two DSRs were field-grown in 2015 and 2016 using two different irrigation regimes:continuous flooding(CF)and AWD.Under CF,no statistical differences in grain yield and WUE were observed between DRRs and DSRs.Irrigation water under the AWD regime was 275–349 mm,an amount 49.8%–56.2% of that(552–620 mm)applied under the CF regime.Compared to CF,AWD significantly decreased grain yield in both DRRs and DSRs,with a more significant reduction in DSRs,and WUE was increased in DRRs,but not in DSRs,by 9.9%–23.0% under AWD.Under AWD,DRRs showed a 20.2%–26.2% increase in grain yield and an 18.6%–24.5% increase in WUE compared to DSRs.Compared to DSRs,DRRs showed less redundant vegetative growth,greater sink capacity,higher grain filling efficiency,larger root biomass,and deeper root distribution under AWD.We conclude that these improved agronomic traits exert positive influences on WUE in DRRs under AWD.

Molecular marker for screening rice cultivars with intermediate amylose content in indica

The waxy(Wx)gene of rice encodes the granule-bound starch synthase(GBSS),which was required in the synthesis of amylose in endosperm.Theamylose content(AC)of rice endosperm played an important role in grain yield,palatability,and processing quality.Our previous researehes showed that en-dosperm AC and GBSS contents were correlated with the ability of excising intron1 from the leader sequence of the Wx transcript.Cultivars with high endosperm

Variation of grain Cd and Zn concentrations of 110 hybrid rice cultivars grown in a low-Cd paddy soil

Enhanced Cd uptake and Zn depletion in rice grains and high potential for food Cd exposure by the high-yielding hybrid cultivars of China had been addressed. A field experiment was conducted in 2006 to determine the difference in grain Cd and Zn between cultivars. Total 110 cultivars including super rice and common hybrid rice cultivars were grown on a single paddy soil （Entic Haplaquept） with a neutral reaction and low total Cd content. Grain Cd and Zn concentrations were determined with graphite atomic adsorption spectrophotometer （GFAAS） and flame atomic adsorption spectrophotometer （AAS） respectively. Wide variation of Cd content in grain was found in a range of 0.004-0.057 mg/kg, while the Zn content in a range of 10.25-30.06 mg/kg among the cultivars. Higher Cd but lower Zn concentration in grains of super rice cultivars was observed compared to the common hybrid ones. A highly significant positive linear correlation of grain Cd/Zn with grain Cd was found for super rice and common hybrid cultivars, meanwhile much higher slope for these hybrid cultivars than the reported non-hybrid cultivars was also observed. Using the limit value of the Chinese chemical guidelines for foods （MOHC and SSC, 2005）, calculated potential risk of food Cd exposure with ＂Zn hungry＂ through diet intake was prominent with all the studied 110 hybrid rice cultivars, possessing high potential health problems for rice production in South China using the super rice cultivars. Breeding of genotypes of rice cultivars with low grain Cd and low Cd/Zn ratio is needed for rice production in acidic red soils where Cd bioavailability is prevalently high.

N Accumulation and Translocation in Four Japonica Rice Cultivars at Different N Rates

Developing high-yielding rice(Oryza sativa L.)cultivars depends on having a better understanding of nitrogen(N) accumulation and translocation to the ear during the reproductive stage.Field experiments were carried out to evaluate the genetic variation for N accumulation and translocation in different Japonica rice cultivars at different N rates and to identify any relationship to grain yield in southeast China.Four Japonica cultivars with similar agronomic characteristics were grown at two experimental sites in 2004 with three N rates of 0,60,and 180 kg N ha^(-1).Dry weights and N contents of rice plants were measured at tillering,initiation,anthesis,and maturity.Grain yields exhibited significant differences (P<0.05)among the cultivars and N application rates.Increasing N rates improved N uptake at anthesis and maturity in all four cultivars(P<0.05).N translocation from vegetative organs to the grains increased with enhanced N rates (P<0.05).N translocation to the grains ranged from 9 to 64 kg N ha^(-1)and N-translocation efficiency from 33% to 68%. Grain yield was linear to N uptake at anthesis(r^2=0.78^(**))and N translocation(r^2=0.67^(**)).Thus,cultivars with a high N uptake at anthesis,low residual N in the straw at maturity,and appropriate low N fertilizer supply in southeast China should efficiently increase N-recovery rate while maintaining grain yield and soil fertility.

Subcellular Cd accumulation characteristic in root cell wall of rice cultivars with different sensitivities to Cd stress in soil

The variations of grain cadmiun（Cd） concentrations, translocation factors（TFs） of Cd from roots to shoots/grains of six rice cultivars, characterized with different Cd-sensitivities in polluted soil were studied, the selected rice cultivars were Xiangzao 17（R1）, Jiayu 211（R2）, Xiangzao 42（R3）, Zhuliangyou 312（R4）, Zhuliangyou 611（R5）, and Jinyou 463（R6）, respectively. The Cd subcellular distribution and Cd binding characteristics on subcellular fractions of rice root cell wall（CW） were further investigated. The results showed that the rice grain Cd contents varied significantly, with a maximum variation of 47.0% among the cultivars, the largest grain Cd content was observed with cultivar R1（Cd-sensitivity cultivar） and the smallest with R5（Cd-tolerance cultivar）. The translocation factors of Cd from roots to shoots（TF_（shoot）） and roots to grains（TF_（grain）） varied greatly among the cultivars. In general, the TFgrain of the cultivars followed the order of R1〉R2〉R3〉R4〉 R6-R5. The Cd concentration（mg kg^（–1） FW） in the fraction of root CW, the fraction of cell wall removing pectin（CW-P） and the fraction of cell wall removing pectin and hemicellulose（CW-P-HC） of the cultivars generally followed the order of CW-P〉CW〉CWP-HC; the ratios of Cd concentration（mg kg–1 FW） in the fraction of CW-P to that of CW were mostly more than 1.10, while the ratios of Cd concentration in the fraction of CW-P-HC to that of CW were mostly less than 0.60, indicating that Cd was mainly stored in the hemicellulose of the root CW. The ratios of Cd of CW-P-HC to CW generally followed the descending order of R1~R2〉R3〉R4〉R5~R6 for the cultivars, which implied that hemicellulose is probably the main subcellular pool for transferring Cd into rice grain, and it restrains the translocation of Cd from shoot to the grain, especially for the Cd-tolerance cultivars（R5 and R6）, the compartmentation of more Cd in hemicellulose in root CW is probably one of the main mechanisms for Cd tolerance of rice cultivars.

Effect of rice cultivar on greenhouse-gas emissions from rice-fish co-culture

In aquaculture,co-culturing rice with fish may mitigate greenhouse-gas emissions.In this study,co-culture of four rice cultivars in a laboratory-scale rice–fish system reduced CH_(4)and N_(2)O emissions relative to fish monoculture.Differences in CH_(4)and N_(2)O emissions among rice cultivars primarily stem from the differential effects of rice plants on plant-mediated CH_(4)transport,CH_(4)oxidation and nitrogen absorption.

High-efficiency breeding of early-maturing rice cultivars via CRISPR/Cas9-mediated genome editing

Rice is a staple food for more than half of the human population.It has been estimated that by 2030,40%more rice needs to be produced in order to meet the growing demand（Khush,2005）.One of the strategies to improve rice productivity is to enlarge rice growth areas, such as the northward expansion of the growth region in Heilongjiang Province, the northernmost region of China （Li et al., 2015）. However, the northward cultivation is accompanied with daylength extension and temperature decrease, which are unfavor- able for rice, a tropical short-day plant, to complete flowering and seed setting. Thus, the need for early-maturing rice cultivars with extremely low photoperiod sensitivity is urgent.

Evaluation of the occluded carbon within husk phytoliths of 35 rice cultivars

Rice is a well-known silicon accumulator. During its periods of growth, a great number of phytoliths are formed by taking up silica via the plant roots. Concurrently, carbon in those phytoliths is sequestrated by a mechanism of long-term biogeochemical processes within the plant. Phytolith occluded C （PhytOC） is very stable and can be retained in soil for longer than a millennium. In this study, we evaluated the carbon bio- sequestration within the phytoliths produced in rice seed husks of 35 rice cultivars, with the goal of finding rice cultivars with relatively higher phytolith carbon sequestra- tion efficiencies. The results showed that the phytolith contents ranged from 71.6 mg. g^-1 to 150.1 mg. g^-1, and the PhytOC contents ranged from 6.4 mg.g^-1 to 38.4 mg.g^-1, suggesting that there was no direct correlation between the PhytOC content and the content of rice seed husk phytoliths （R = 0.092, p 〉 0.05）. Of all rice cultivars, six showed a higher carbon sequestration efficiency in phytolith seed husks. Additionally, the carbon bio- sequestration within the rice seed husk phytoliths was approximately 0.45-3.46 kg-e-CO2-ha^-1. yr^-1. These rates indicate that rice cultivars are a potential source of carbon biosequestration which could contribute to the global carbon cycle and climate change.

Sources of Nitrogen in Combination with Systems of Irrigation Influence the Productivity of Modern Rice(Oryza sativa L.)Cultivars during Dry Season in Sub-Tropical Environment

In irrigated agricultural systems,nitrogen(N)and water are the vital resources for sustainability of the crop production in the modern era of climate change.The current study aimed to assess the impact of water and N management on the productivity of irrigated rice cultivars.In the context,a field observation was done at the research farm of Bangladesh Agricultural University,Mymensingh,during dry seasons in consecutive two years(2018–2019 and 2019–2020).The experiments were set up following split-plot design assigning water management in the main plots,nitrogen management in the sub-plots,and the cultivars were approved in the split-split plot with three replications.After two years observation,it was revealed that rice cultivar Binadhan-8 gave the maximum value of leaf area index,number effective tillers hill-1 and grains panicle-1 which lead to the higher grain yield(GY).Substantial relationships were observed among the concentration of N,growth,total dry matter(TDM)and N content,N uptake,N utilization effectiveness,and GY.However,with little exception,the Combined effect of water and N,cultivars and water management were varied significantly for all parameters.Finally,the results of the current study concluded that application of irrigation at 8 days after the disappearance of ponded water and source of 105 kg N ha-1 from PU+Poultry manure are the best management approach for the excellent performance of rice cultivar Binadhan-8.

Screening of Drought Resistance Identification Indexes for Rice(Oryza sativa L.) Cultivars in Ningxia

The morphological characters, physiological characters, yield traits and yield per plant of total 49 rice cultivars from Ningxia were investigated under conditions of water stress and non-water stress so as to determine the relationship between each trait and yield per plant under water stress and the relationship between each relative character and drought resistance coefficient under water stress and non-water stress. The correlation, grey correlation, stepwise regression and path analyses showed that the tiller number per plant, plant height, grain density, effective panicle number per plant and grain number per panicle, total 5 traits, were significantly correlated with the drought resistance of rice, and they could be used to identify the drought resistance of rice in Ningxia. In addition, the drought resistance of rice was graded qualitatively according to the subordinate function value of corresponding drought resistance coefficient. The results showed that among the 49 rice cultivars from Ningxia,6 rice cultivars were highly drought resistant, and 9 rice cultivars were moderately drought resistant, suggesting that the evaluation method was feasible and effective.

Response of Photosynthesis, Growth, Carbon Isotope Discrimination and Osmotic Tolerance of Rice to Elevated CO_2

Four rice ( Oryza sativa L.) cultivars 'IR72', 'Tesanai 2', 'Guichao 2' and 'IIyou 4480' were grown in two plastic house (15 m×3 m) with 35 μmol/mol and 60 μmol/mol CO 2 concentration which was controlled by computer. As compared with rice at ambient 35 μmol/mol CO 2, the changes in photosynthetic rate at elevated CO 2 showed up_regulation ('IR72' and 'Tesanai 2'), stable (unchanged) in 'Guichao 2' and down_regulation type ('IIyou 4480'). Growth rate, panicle weight, integrated water use efficiency (WUE) calculated from Δ 13 C and the capacity of scavenging DPPH · (1,1_diphenyl_2_picrylhydrazyl) free radical were increased at elevated CO 2. An increment in total biomass was observed in three cultivars by elevated CO 2, with the exception of 'IIyou 4480'. Ratios of panicle weight/total biomass were altered to different extents in tested cultivars by elevated CO 2. When leaf segments were subjected to PEG osmotic stress, the electrolyte leakage rate from leaves grown at elevated CO 2 was less than that at 35 μmol/mol CO 2. Those intraspecific variations of rice imply a possibility for selecting cultivars with maximal productivity and high tolerance to stresses adapted to elevated CO 2 in the future.

Effect of Nitrogen Fertilization on Yield and Quality of Aromatic Rice in North-Western Indo-Gangetic Plains

Most of the aromatic rice cultivars are susceptible to disease, insect-pest attack and are more prone to lodging. Therefore, nitrogen is the key input for increasing the productivity of aromatic rice. Research analyzing the effects of N level on yield and quality characteristics of modem aromatic cultivars in the north-western Indo-Gangetic Plains is not well documented. Therefore, the present study was conducted to optimise the N levels for higher yield and better quality of the modem aromatic rice cultivars. The mean grain yield increased by 22.5% when plots were supplemented with 40 kg/ha of N application as compared to control （unfertilized）. Among cultivars, Punjab Mehak 1 registered highest yield （5.3 t/ha） followed by Pusa Basmati 1121 （4.78 t/ha） and Punjab Basmati 2 （4.66 t/ha） respectively. Interactive effect between N levels and cultivars on grain yield revealed that in Punjab Mehak l, grain yield responded significantly up to 60 kg/ha of N application as compared to Pusa Basmati 1121 and Punjab Basmati 2 where it responded only upto 40 kg/ha of N application. All the quality characteristic found to be improved with N application, whereas amylose content decreased with 60 kg/ha of N application as compared to 20 and 40 kg/ha of N application.

Effect of Potassium Nutrition of Different Varieties of Rice on the Redox Status in Microzone Rhizosphere Soils

Being divided into three groups-strong, moderate and weak-according to the different kinetic parameters (Fmax, km, Cmin) of potassium uptake by crops, 21 cultivars of rice have been studied to find out the relationships between their potassium nutrition and the oxidation-reduction status in the rhizosphere soils.Results show that, with no application of K fertilizer, there were higher contents of active reducing substances and ferrous iron in rhizosphere soils planted with cultivars, such as Zhongguo 91, week in absorbing potassium than in soils cropped with cultivars, Shanyou 64, stronger in absorbing potassium. As a result of K application, however, these toxic substances were decreased appreciably in the soil, particularly in the root zone where weakly K-absorbing cultivars were growing, and the parameter of soil redox (pH +pE) was increased, the most striking example of this being found in the rhizosphere soil where the more strongly K-absorbing cultivars were growing. On and close to the root surface in soils where rice plants were supplied with potassium fertilizer, rather more iron oxide had been accumulated compared with rice receiving no potash, and even greater amounts of red iron oxide precipitated on the rice root in neutral paddy soils. As shown by the concentration distribution of active reducing substances and ferrous iron in a microzone of the profile, the redox range of rice roots supplied with potassium may extend as far as several centimeters from the root surface. It can thus be seen that potassium nutrition exerts its effect first on the morphological properties of rice roots and their exudation of oxygen, then on the content of soluble oxygen and the count and species of oxygen-consuming microbes in the rhizosphere soil, and finally on the redox status of the soil.

Diversity Centers of Rice Cultivar in Yunnan and Their Correlation with Ecological and Cultural Factors

Ecological and cultural factors have strong impacts on the distribution and cultivation of agricultural cultivar., In this paper, the correlation between diversity centers of rice cultivar and ecological, cultural factors was probed, based on datasets of rice cultivar in Yunnan, Southwest China. The results showed that diversity centers of rice cultivar were observed in Southwest Yunnan, South Yunnan and Southeast Yunnan, which may be related to the local culture of rice production and warm, humid climate. For the diversity center in South Yunnan, culture of rice production of Dai and Hani people may play important roles. The diversity center in Southwest Yunnan may relate to the culture of rice production of Dai, Jingpo and Lahu people, and for the diversity center in Southeast Yunnan, Miao, Yao and Zhuang people＇s culture in rice production can not be underestimated. Traditional culture promoted the cultivation of rice cultivars, and high diversity of rice cultivars facilitate the preservation and continuation of the traditional culture as well.

Cultivar-dependent rhizobacteria community and cadmium accumulation in rice: Effects on cadmium availability in soils and iron-plaque formation

The association between the rhizospheric microbial community and Cd accumulation in rice is poorly understood.A field trial was conducted to investigate the different rhizobacterial communities of two rice cultivars with high Cd accumulation(HA)and low Cd accumulation(LA)at four growth stages.Results showed that the Cd content in the roots of the HA cultivar was 1.23-27.53 higher than that of the LA cultivar(0.08-10.5μg/plant)at four stages.The LA cultivar had a significantly lower Cd availability in rhizosphere and a higher quantity of iron plaque(IP)on the root surface than the HA cultivar at four stages.This resulted in the reduction of Cd concentration in IPs and Cd translocation from IP-to-root.Microbial analysis indicated that the LA cultivar formed a distinct rhizobacterial community from the HA cultivar and had lessα-diversity.The rhizosphere of the LA cultivar was enriched in specific bacterial taxa(e.g.,Massilia and Bacillus)involved in Cd immobilization by phosphate precipitation and IP formation by iron oxidization.However,the rhizosphere in the HA cultivar assembled abundant sulfur-oxidizing bacteria(e.g.,Sulfuricurvum)and iron reduction bacteria(Geobacter).They promoted Cd mobilization and reduced IP formation via the metal redox process.This study reveals a potential approach in which specific rhizobacteria decrease or increase Cd accumulation in rice on contaminated soil and provides a new perspective for secure rice production.