Effect of Supplied P Levels on Rice Growth and Uptake of P and Zn in Different P-Efficiency Genotypes

A soil pot culture experiment with four supplied P levels （i.e. P30, P50, P100, P200, representing supplemental P 30, 50, 100, 200 mg/kg, respectively） was conducted to investigate uptake and use ability to P and Zn in the rice genotypes with different P-efficiency, of which rice genotypes 508, 99011, 580, 99112 were Iow-P tolerant and 99056, 99012 were Iow-P sensitive. Low-P tolerant rice 580 and 99011 absorbed more P than the others, and rice genotype 580 had stronger uptake ability especially at Iow-P level such as P50 and P30. 508 could absorb considerable P, and had the lowest P percentage of shoot, indicating it had good performance in P-use efficiency. These three rice genotypes had larger biomass and less response to changed P level than rice genotype 99112, 99056 and 99012. Rice genotype 99112 showed Low-P tolerance mainly by sacrificing biomass to maintain high relative grain yield. The least amount of P absorbed by 99056 showed it had the lowest P uptake efficiency, and the highest P percentage in shoot of 99012 meant it had the lowest P use efficiency. So they two showed Iow-P sensitivity. Zn contents in shoot under P200, P100 and P50 were similar, but P30 increased Zn content in shoot significantly. The Zn contents in shoot of 99112, 99056 and 99012 were higher than those of 508, 99011 and 580, especially at tillering stage and booting stage. As for total Zn content in shoot, Low-P tolerant rice genotype 580 had the largest amount and followed by 99011 and 508, Iow-P tolerant rice genotype 99012 had the smallest amount at the three sampling stage and followed by 99056. Furthermore, P/Zn in shoot of 99012 was the highest, and that of 99056 was the smallest at the same P level.

Local nitrogen application increases maize post-silking nitrogen uptake of responsive genotypes via enhanced deep root growth

Nitrogen(N)is unevenly distributed throughout the soil and plant roots proliferate in N-rich soil patches.However,the relationship between the root response to localized N supply and maize N uptake efficiency among different genotypes is unclear.In this study,four maize varieties were evaluated to explore genotypic differences in the root response to local N application in relation to N uptake.A split-root system was established for hydroponically-grown plants and two methods of local N application(local banding and local dotting)were examined in the field.Genotypic differences in the root length response to N were highly correlated between the hydroponic and field conditions(r>0.99).Genotypes showing high response to N,ZD958,XY335 and XF32D22,showed 50‒63%longer lateral root length and 36‒53%greater root biomass in N-rich regions under hydroponic conditions,while the LY13 genotype did not respond to N.Under field conditions,the root length of the high-response genotypes was found to increase by 66‒75%at 40‒60 cm soil depth,while LY13 showed smaller changes in root length.In addition,local N application increased N uptake at the post-silking stage by 16‒88%in the high-response genotypes and increased the grain yield of ZD958 by 10‒12%.Moreover,yield was positively correlated with root length at 40‒60 cm soil depth(r=0.39).We conclude that local fertilization should be used for high-response genotypes,which can be rapidly identified at the seedling stage,and selection for“local-N responsive roots”can be a promising trait in maize breeding for high nitrogen uptake efficiency.

The Difference in Growth and Four Microelement Concentrations Between Two Rice Genotypes Differing in Grain Cadmium-Accumulating Capacity

A pot experiment was conducted with two rice genotypes having different Cd concentrationsin their grains to study the effect of soil Cd level on biomass, Cd and Fe, Zn, Cr andPb accumulation in different plant parts. Cd was added into soil to form 4 levels, i.e.,0, 0.5, 2.5 and 12.5mgkg-1, respectively. The results showed that the Cd-induced reductionin biomass accumulation varied in both genotypes and growth stages. The Cd-inducedreduction in biomass became less with the progress of growth, and Xiushui63, a genotypewith relatively higher grain Cd concentration, was more severely inhibited than Xiushui217,a relatively lower Cd concentration. Both Cd concentration and accumulation in thevarious plant parts increased substantially with the increase of Cd levels. The differencebetween two genotypes in Cd concentration and accumulation became more pronounced withincreased Cd level as well as prolonged duration of exposure. Xuishui63 had much greaterCd accumulation than Xiushui217, in particular at late growth stage. Xuishui63 had aremarkably higher Cd translocation of roots to shoots than Xiushui217 in all Cd levels.The effect of Cd addition on four microelement concentrations in straw and milled ricealso varied in genotypes and Cd levels. Without Cd addition, Xiushui63 was significantlylower than Xiushui217 in the concentrations of all four elements in straw, while the casewas just opposite in milled rice. Zn, Fe and Pb concentrations decreased in milled ricewith the increase of Cd level, although the reduction extent differed in two genotypes.The results indicated that Cd concentration in rice grain is primarily dependent on theshoot Cd concentration, which is in turn mainly determined by Cd translocation from rootsto shoots.

Differences in the Efficiency of Potassium(K) Uptake and Use in Five Apple Rootstock Genotypes

Plants that grow well while accumulating and transporting less potassium（K） perform better than more-sensitive plants when under deficiency conditions, which makes low-K-input and environmentally friendly agriculture possible. We conducted hydroponics and sand culture experiments to evaluate the efficiency of various apple（Malus domestica Borkh） rootstocks in their K uptake and utilization. Five genotypes were selected which are widely used in China- M. hupehensis Rehd, M. prunifolia Borkh, M. robusta Rehd, M. sieversii Roem, and M. rockii Rehd. Plant heights, root and shoot dry weights, and K concentrations were recorded. These genotypes differed markedly in dry weights, absolute and relative K concentrations, absolute and relative K accumulations, and their K efficiency ratio under deficient K conditions. The last parameter, expressed as relative shoot dry weight, was strongly and positively correlated with the other four parameters in each genotype. Therefore, we suggest that this parameter could serve as an index when selecting K-efficient genotypes. In this study, we have determined that M. sieversiiand M. rockii are K-inefficient genotypes; M. prunifolia is K-efficient genotype; M. hupehensis and M. robusta have moderate levels of potassium efficiency.

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.

Genotypic Differences in Growth and Physiological Responses to Transplanting and Direct Seeding Cultivation in Rice

The field experiments were conducted to investigate the growth and physiological responses of six super hybrid rice combinations to two planting methods, transplanting （TP） and direct seeding （DS） during 2006-2007 and 2007-2008. The 1000-grain weight and number of tillers per plant at the early growth stage, the maximum quantum yield of PSII （Fv/Fm） and transpiration rate （Tr） were higher in DS plants than in TP ones, whereas the grain yield, number of panicles per square meter, seed setting rate, net photosynthetic rate （Po） and stomatal conductance were lower in DS plants. However, little difference was detected in number of grains per panicle, stem （shoot） and leaf weight between the combinations in the two planting methods. The responses of plant growth and physiological traits to planting method differed greatly among the six combinations. In both planting methods, Chouyou 58 and Yongyou 6 had the highest and lowest panicle biomass and Pn, respectively. The higher yield of Chunyou 58 was associated with more numbers of panicles per square meter and grains per panicle in both planting methods. The results indicate that lower grain yield in DS relative to TP is attributed to more excessive tillers at the early stage, lower leaf biomass and photosynthetic rate at the late stage.

Cd Toxicity and Accumulation in Rice Plants Vary with Soil Nitrogen Status and Their Genotypic Difference can be Partly Attributed to Nitrogen Uptake Capacity

Two indica rice genotypes, viz. Milyang 46 and Zhenshan 97B differing in Cd accumulation and tolerance were used as materials in a hydroponic system consisting of four Cd levels （0, 0.1, 1.0 and 5.0 μmol/L） and three N levels （23.2, 116.0 and 232.0 mg/L） to study the effects of nitrogen status and nitrogen uptake capacity on Cd accumulation and tolerance in rice plants. N-efficient rice genotype, Zhenshan 97B, accumulated less Cd and showed higher Cd tolerance than N-inefficient rice genotype, Milyang 46. There was consistency between nitrogen uptake capacity and Cd tolerance in rice plants. Increase of N level in solution slightly increased Cd concentration in shoots but significantly increased in roots of both genotypes. Compared with the control at low N level, Cd tolerance in both rice genotypes could be significantly enhanced under normal N level, but no significant difference was observed between the Cd tolerances under normal N （116.0 mg/L） and high N （232.0 mg/L） conditions. The result proved that genotypic differences in Cd accumulation and toxicity could be, at least in part, attributed to N uptake capacity in rice plants.

Analysis of genotype differences of rice response to low Zn^(2+) activity and some morphological characteristics

Zinc deficiency is one of the most widespreadmicro-nutritional disorder for rice. To solve the problem, screening Zn-efficient cultivars isan available method and understanding geno-

Response of Iron Content in Milled Rice to Nitrogen Levels and Its Genotypic Differences

To investigate the effect of nitrogen （N） level on iron （Fe） content in milled rice, a field experiment was carried out under three N application levels including 0, 150 and 300 kg/hm2 by using 120 rice genotypes. In addition to the genotypic differences of iron content in milled rice, grain yield, 1000-grain weight and N content in grains under the same N level, there were also variations in the response of Fe content in milled rice to N levels. Based on the range and variation coefficient of Fe content in milled rice under the three N levels, the response of Fe content in milled rice to N levels could be classified into four types including highly insensitive, insensitive, sensitive and highly sensitive types. A significant quadratic correlation was found between the Fe content in milled rice and 1000-grain weight or the N content in grains. However, no significant correlation between the Fe content in milled rice and grain yield was detected. In conclusion, there are genotypic differences in the effects of N levels on Fe content in milled rice, which is favorable to breeding of Fe-rich rice under different N environments. Furthermore, high yield and Fe-rich rice could be grown through the regulation of nitrogen on Fe content in milled rice, 1000-grain weight and N content in milled rice.

Transport of cadmium from soil to grain in cereal crops: A review

Due to rapid urbanization and industrialization, many soils for crop production are contaminated by cadmium(Cd), a heavy metal highly toxic to many organisms. Cereal crops such as rice, wheat, maize, and barley are the primary dietary source of Cd for humans, and reducing Cd transfer from soil to their grains is therefore an important issue for food safety. During the last decade, great progress has been made in elucidating the molecular mechanisms of Cd transport, particularly in rice. Inter-and intraspecific variations in Cd accumulation have been observed in cereal crops. Transporters for Cd have been identified in rice and other cereal crops using genotypic differences in Cd accumulation and mutant approaches. These transporters belong to different transporter families and are involved in the uptake, vacuolar sequestration, root-to-shoot translocation, and distribution of Cd. Attempts have been made to reduce Cd accumulation in grains by manipulating these transporters through overexpression or knockout of the transporter genes, as well as through marker-assisted selection breeding based on genotypic differences in Cd accumulation in the grains. In this review, we describe recent progress on molecular mechanisms of Cd accumulation in cereal crops and compare different molecular strategies for minimizing Cd accumulation in grains.

Genotypic differences in callus induction and plant regeneration from mature embryos of barley(Hordeum vulgare L.)

An efficient induction system and regeneration protocol based on mature barley embryos were developed.Embryos isolated from mature seeds,dehusked by hand and inoculated with longitudinally bisected sections,showed low contamination and high primary callus-forming capability.The influences of nine culture media on primary callus induction and germination from the mature embryos of barley cultivars Golden Promise and Zaoshu 3 were analyzed.The results showed that the two cultivars had much higher values of primary callus induction in the B16M6D medium as compared to the other eight medium formulations,with a frequency of 74.3% and 78.4% for Golden Promise and Zaoshu 3,respectively.Furthermore,Zaoshu 3 demonstrated particularly high stability in callus induction over the different media,indicating its potential utilization in callus induction and regeneration for its good agronomic traits and wide adaption.There were significant differences amongst 11 barley genotypes in terms of primary callus induction in the optimum medium,with percentages of callus induction and germination response ranging from 17.9% to 78.4% and 2.8% to 47.4%,respectively.Green plantlets of Dong 17,Golden Promise,and Zaoshu 3 were successfully de-veloped from primary calli through embryogenesis,with green plant differentiation frequencies ranging from 9.7% to 21.0% across genotypes.