Effect of Cd on the growth,dry matter accumulation and grain yield of different rice cultivars

Pot soil experiments showed that there were great variations among six rice cultivars in their tolerance to soil Cd stress, with respect to tillering, plant height, leaf area, dry matter accumulation and grain yield. Some cultivars were highly tolerant of Cd and showed little toxicity under high levels of soil Cd stress (100 mg kg^?1), while others were much more sensitive. Roots were not necessarily more sensitive than above‐ground parts, but the diversities among rice cultivars with regard to the relative changes in dry matter accumulation under soil Cd stress were greater in roots than those observed in straw and grain. The toxicity effects of Cd on rice growth and development lessened as plants grew and matured, indicating that rice plants show adaptation and growth compensation in response to soil Cd stress during prolonged exposure. The relative change in the number of grains per panicle showed a strong positive correlation with relative change in grain yield and, of the four grain yield components measured (panicles per pot; grains per panicle; filled grain percentage; weight per grain), it appeared to be the one most influenced by Cd stress. Thus the reduction of grains per panicle is the main cause of grain yield loss under soil Cd stress. Copyright © 2007 Society of Chemical Industry     

Differences in physicochemical properties of kernels of two rice cultivars during grain formation

BACKGROUND: Rice varieties with similar apparent amylose content may have different grain qualities. The development of rice quality is a dynamic process that occurs with the formation of rice kernels. In this study, physicochemical properties during the grain formation period were investigated to interpret differences in grain quality between two non‐waxy rice cultivars, Wuyujing3 and 30you917, with similar apparent amylose content. RESULTS: There were significant differences in dynamic changes in 1000‐grain weight, amylose content and pasting and thermal properties during grain formation of the two cultivars. The difference in their apparent amylose contents from 5 days after anthesis (DAA) to 15 DAA was significant, except in the late grain‐filling stage. Wuyujing3 showed a slower increase in 1000‐grain weight than 30you917 from 10 to 25 DAA. The transition temperatures (T_o, T_p and T_c) of developing grain flour of Wuyujing3 were higher than those of 30you917 during the grain formation period. Wuyujing3 showed greater stickiness (higher breakdown and peak viscosity and lower positive setback) than 30you917 according to Rapid Visco Analyser (RVA) profiling. CONCLUSION: The results suggested that the differences in cooking and eating quality parameters of the two mature rices were determined by the differences in grain filling and the dynamic changes in the main rice quality components such as amylose content, grain weight and differential scanning calorimetry and RVA properties, which will help cultivators understand the physical basis of rice quality development. Copyright © 2011 Society of Chemical Industry     

Genetic dissection of amino acid content in rice grain

BACKGROUND: Protein content and amino acid composition in rice are the most important components of rice nutrient quality. However, there have been few reports on the mapping of quantitative trait loci (QTLs) for the contents of protein and amino acids in rice grain and other crops (soybean, corn). In this study a population of 241 recombinant inbred lines (RILs) from a cross between Zhenshan 97 and Minghui 63 (the parents of the most widely grown hybrid rice in China) was constructed to detect the main effect and epistatic effect QTLs for amino acid content (AAC) as characterised by individual AACs, total essential AAC and total AAC. RESULTS: Using a linkage map covering a total of 1796 centimorgan (cM) based on 221 molecular marker loci, a total of 12 QTLs were identified for ten traits mapped on chromosomes 1, 4, 6, 7 and 11. The QTL cluster (flanked by C904, R2632 and C39) on chromosome 1 was associated with the content of eight amino acids. The phenotypic variation explained by individual QTLs ranged from 3.4 to 48.8%. Eighty‐one digenic interactions were resolved that involved 143 loci distributed on all 12 chromosomes. The amount of variation explained by main effect QTLs was lower than that explained by QTLs involved in epistatic interactions. CONCLUSION: The findings showed that most main effect QTLs for AACs detected tended to be co‐localised within the genome. Thus, if a breeder were interested in changing the concentration of only one amino acid, this might be difficult to achieve. Meanwhile, the prevalent epistasis for the loci involved appeared to hold true for the content of amino acids. The information reported in the present study is expected to be useful for future breeding programmes targeting the development of improved rice amino acid composition for human nutrition. Copyright © 2009 Society of Chemical Industry     

Impact of cultivar variation in grain density of rice panicle on grain weight and quality

BACKGROUND: In the last two decades, newly released rice cultivars in southeastern China have been mainly characterised by more grains per cm panicle (GPCP), i.e. a compact panicle. These compact panicle cultivars show high yield potential but inferior quality. Accordingly, experiments were conducted to study the effect of GPCP on grain weight and quality. RESULTS: Two compact panicle and two loose panicle cultivars of japonica rice were used to investigate the effect of GPCP on the variation in grain weight and quality within a panicle. Significant differences in grain quality, including brown rice length, width and length/width ratio, brown rice and head‐milled rice percentages, chalky grain percentage and amylose and protein contents, were found among grains within a panicle. In general, the compact panicle cultivars showed lower grain weight and larger variation in brown rice length, width and length/width ratio, chalky grain percentage and amylose content among grains within a panicle than the loose panicle cultivars. CONCLUSION: GPCP is negatively associated with quality uniformity, and increasing the grain number on top secondary rachises may reduce the variation in grain weight and quality within a panicle. Copyright © 2008 Society of Chemical Industry     

Influence of free‐air CO2 enrichment (FACE) on the eating quality of rice

Rice plants (Oryza sativa L cv Akitakomachi) were grown under free‐air CO₂ enrichment (FACE) in farmers' fields in Shizukuishi, Iwate, Japan during 1999 and 2000. The grains were harvested and subsequently analyzed for protein and amylose contents as well as the traits related to cooked‐rice viscosity. The cooked rice was also subjected to sensory evaluation. The protein content of rice grains grown under elevated CO₂ was significantly lower than that of rice grown under ambient conditions. In addition, CO₂ enrichment increased the whiteness of the grains in both brown and milled rice and reduced their surface hardness. Although the amylose content of rice grains was unaffected, starch pasting properties demonstrated that rice grains in elevated CO₂ had higher maximum viscosity and breakdown than those grown in ambient conditions. Sensory evaluation of cooked rice with respect to umami (deliciousness), appearance, aroma, hardness, stickiness and overall palatability index indicated that the sensory properties were not significantly altered by the CO₂ enrichment treatment. Therefore, we conclude that the growth of the rice cultivar Akitakomachi under elevated CO₂ concentration decreased the protein content, but did not change the palatability to a level that may be detected by sensory taste panel evaluation. Copyright © 2005 Society of Chemical Industry     

Genetic analysis of developmental behavior for amylose content in filling process of rice

Dynamic genetic effects for amylose content (AC) of indica rice were analyzed at four different filling times/stages using the genetic models for quantitative traits. The expression of triploid endosperm, cytoplasmic and diploid maternal plant genes were important for AC at different developmental stages of rice, especially at the early and middle filling stages. AC of rice was mainly controlled by the cumulative or net endosperm effects and their genotype × environment interaction effects, except at late filling stage which the net maternal effects were larger. The expression of genes at day 7, 14 or 21 after flowering was more easily influenced by the environmental conditions, while the genes' expression at mature stage of rice was stable. Breeding improvement could be achieved by selection for a better variety with a suitable AC because of the larger additive and cytoplasmic effects. The total narrow‐sense heritabilities for AC on days 7, 14, 21 and 28 after flowering were 78.9, 85.6, 80.1 and 70.2%, respectively. The interaction heritability was more important than the general heritability, except at the maturing time of rice. Significant genotypic correlations for AC were observed among developmental times of rice. Copyright © 2004 Society of Chemical Industry