Percentage Of Chalky Grains Research Articles

Rapid production of novel beneficial alleles for improving rice appearance quality by targeting a regulatory element of SLG7.

Rapid production of novel beneficial alleles for improving rice appearance quality by targeting a regulatory element of SLG7.

Inter-relações genéticas de causa e efeito para atributos de qualidade de grãos de arroz irrigado

Abstract The objective of this work was to determine the genetic correlations and the direct and indirect associations of agronomic traits and grain quality attributes with the percentage of whole grains in flood irrigated rice. The experiment was carried out in two environments, in a randomized complete block design with three replicates, using 23 irrigated rice genotypes. The evaluated traits were: percentage of whole grains, caryopsis length, caryopsis width, panicle length, panicle weight, 1,000 grain weight, days to flowering, percentage of chalky grains with white belly, total chalky area, total whiteness, vitreous whiteness, and defects in coloring. The percentage of grains with white belly and total chalky area were positively correlated, whereas the percentage of grains with white belly and vitreous whiteness were negatively correlated. The traits caryopsis width, percentage of chalky grains with white belly, panicle weight, and 1,000 grain weight showed indirect effects on whole-grain yield response according to total chalky area and total whiteness. Total chalky area and total whiteness are the factors that most negatively influence the percentage of whole grains according to the genotypic correlations and direct effects.

Daytime warming during early grain filling offsets the CO2 fertilization effect in rice

Increasing concentrations of atmospheric CO2 are projected to have positive effects on crop photosynthesis and yield (CO2 fertilization effect, CFE). High-temperature events, such as heatwaves, during sensitive periods can have significant negative impacts on crop yield and quality; however, the combined effects of elevated CO2 (EC) and short-period elevated temperature (ET) have not been determined in the open field. Here, we show a strong negative interaction between EC and ET obtained from a temperature-free-air controlled enhancement treatment embedded in a season-long free-air CO2 enrichment (FACE) experiment on a japonica rice cultivar, Koshihikari, over three seasons at the Tsukuba FACE facility in Ibaraki, Japan. CFE was 15% at ambient temperature, but it was reduced to 3% by ET, where canopy surface temperature (Tc) was elevated by ∼1.6 °C for 20 d after flowering. Reductions in CFE mainly arose from poor grain setting at Tc above ∼30 °C. High Tc also increased the percentage of chalky grains and substantially decreased the grain appearance quality, although the threshold temperature varied between the seasons. Simultaneous increases in atmospheric CO2 concentration and air temperature are expected to increase daytime canopy temperatures more than air warming alone, thereby affecting grain yield and quality. Crop models without these processes are likely to underestimate the negative impacts of climate change on crop yield and quality. The development of adaptation measures against heat stress, particularly during reproductive and grain-filling periods, needs to be enhanced and accelerated.

Fine mapping of two grain chalkiness QTLs sensitive to high temperature in rice

BackgroundGrain chalkiness is one of important factors affected rice grain quality. It is known that chalkiness is affected by the high temperature during the seed filling period. Although a larger of QTLs for chalkiness were reported across all 12 chromosomes, only a few of the QTLs were fine mapped or cloned up to now. Here, we fine map two QTLs for chalkiness in two single-segment substitution lines (SSSLs), 11–09 with substitution segment from O. sativa and HP67–11 with substitution segment from O. glaberrima.ResultsThe grain chalkiness of SSSLs 11–09 and HP67–11 was significantly lower than that in the recipient Huajingxian 74 (HJX74) in consecutive 8 cropping seasons. The regression correlation analysis showed that percentage of chalky grain (PCG) and percentage of chalky area (PCA) were significantly and positively correlated with percentage of grain chalkiness (PGC). Two QTLs for grain chalkiness were located on two chromosomes by substitution mapping. qPGC9 was mapped on chromosome 9 with an estimated interval of 345.6 kb. qPGC11 was located on chromosome 11 and delimited to a 432.1 kb interval in the O. sativa genome and a 332.9 kb interval in the O. glaberrima genome. qPGC11 is a QTL for grain chalkiness from O. glaberrima and was mapped in a new region of chromosome 11. The effect of two QTLs was incomplete dominance. The additive effects of two QTLs on chalkiness in second cropping season (SCS) were significantly greater than that in first cropping season (FCS).ConclusionsqPGC11 is a new QTL for grain chalkiness. The two QTLs were fine mapped. The donor alleles of qPGC9 and qPGC11 were sensitive to the high temperature of FCS.

The effects of dry cultivation on grain‐filling and chalky grains of upland rice and paddy rice

AbstractAn important challenge facing rice production in China is to solve the problem of declining freshwater supply without affecting grain yield and quality. The purpose of this study was to investigate the effects of cultivation methods on the grain‐filling and chalk grains of Zhonghan 3 (Japonica) upland rice and Wuxiangjing 99–8 (Japonica) paddy rice. Both cultivars were cultivated in fields under three cultivation methods: continuous flooding (CF) as a control, bare dry cultivation (BC), and plastic film mulching dry cultivation (PFMC). Compared with CF, the yield of the upland rice decreased significantly, and the yield of paddy rice did not differ significantly under PFMC. The yields of both cultivars decreased significantly under BC. Superior and inferior grains of the two cultivars under PFMC had a greater mean grain‐filling rate (G) and a shorter active grain‐filling time (D). Under PFMC, the two cultivars had a higher export translocation rate of the matter from the stem and sheath and a slower decrease of the chlorophyll content in the flag leaves and nitrogen content in the plants after heading. Upland rice had a higher grain weight, and paddy rice had a lower grain weight compared to CF. The chalkiness of the two cultivars was significantly lower under dry cultivation than under CF. The correlation analysis showed that the percentage of chalky grains was negatively correlated with G and positively correlated with D, indicating that dry cultivation could improve the grain‐filling rate and appearance quality of the two cultivars.

Association analysis between constructed SNPLDBs and GCA effects of 9 quality-related traits in parents of hybrid rice (Oryza sativa L.)

BackgroundThe general combining ability (GCA) of parents in hybrid rice affects not only heterotic level of grain yield and other important agronomic traits, but also performance of grain quality traits of F2 bulk population which is the commodity consumed by humans. In order to make GCA improvement for quality traits in parents of hybrid rice by molecular marker assisted selection feasible, genome-wide GCA loci for quality traits in parents were detected through association analysis between the effects of GCA and constructed single nucleotide polymorphism linkage disequilibrium blocks (SNPLDBs), by using unhusked rice grains harvested from F1 plants of 48 crosses of Indica rice and 78 crosses of Japonica rice. GCA-SNPLDBs association analysis.ResultsAmong the 8 CMS and 6 restorer lines of indica rice subspecies, CMS lines Zhenpin A, Zhenshan97 A, and 257A, and restorers Kanghui98, Minghui63 and Yanhui559 were recognized as good general combiners based on their GCA effect values for the 9 quality traits (brown rice rate, milled rice rate, head rice rate, percentage of chalky grains, chalky area size, chalkiness degree, gelatinization temperature, gel consistency and amylose content). Among the 13 CMS and 6 restorer lines of japonica rice subspecies, CMS 863A, 6427A and Xu 2A, and restorers C418, Ninghui8hao and Yunhui4hao showed elite GCA effect values for the 9 traits. GCA-SNPLDB association analysis revealed 39 significant SNPLDB loci associated with the GCA of the 9 quality-related traits, and the numbers of SNPLDB loci located on chromosome 1, 2, 3, 4, 5, 8, 9, 11 and 12 were 1, 4, 3, 9, 6, 5, 5, 4 and 2, respectively. Number of superior GCA alleles for the 9 traits among the 33 parents ranged from 1 to 26.ConclusionsThirty-nine significant SNPLDBs loci were identified associated with the GCA of 9 quality-related traits, and the superior SNPLDB alleles could be used to improve the GCA of parents for the traits in the future by molecular marker assisted selection. The genetic basis of trait GCA in parents is different from that of trait itself.

Effects of short-term heat stress at booting stage on rice-grain quality

Extreme heat-stress events are becoming more frequent under anticipated global warming, which is having devastating effect on grain yield, as well as quality, of rice (Oryza sativa L.). The effects of heat stress at booting stage on grain quality of two japonica varieties, Nanjing41 and Wuyunjing24, were investigated in phytotrons during 2014 and 2015. Rice plants were subjected to four mean temperature regimes 27°C, 31°C, 35°C and 39°C of 2, 4 and 6 days’ duration. The results showed that high temperatures of 35°C and 39°C for 4 and 6 days significantly reduced panicle size, seed-setting rate, grain size, chalky grain rate, milling characteristics and amylose content, but increased protein content. Severe heat stress decreased values of peak viscosity and breakdown, and increased pasting temperature. An increase in heat degree-days decreased the percentage of chalky grains exponentially, and decreased amylose content and increased protein content linearly. Sensitivity of grain quality to heat stress in the two varieties differed among quality traits and with heat stress intensity. This study indicates that rice-grain quality had some resistance to mild heat stress, but it could not withstand severe heat stress at booting. Short-term heat stress at booting stage deteriorates most grain-quality traits, posing a potential risk to rice quality. The impacts on grain quality could be well quantified by the combined effects of the intensity and duration of heat stress at booting stage.

Identification of genome-wide SNPs associated with combining ability for grain quality traits in parents of hybrid japonica rice (Oryza sativa L.)

Improving the combining ability for grain quality traits of the parents is the key factor to enhance averaged bulk grain quality of hybrid japonica rice. Eight quality traits including brown rice rate, milled rice rate (MRR), head rice rate (HRR), chalkiness degree (CD), percentage of chalky grain (PCG), alkali spreading value (ASV), gel consistency (GC) and amylose content (AC) of the bulked sample of rough rice harvested from the 81 F1 hybrid plants were investigated in 2014 and 2015. By combining the phenotypic data of general combining ability (GCA) for the quality traits with genotypic data of single nucleotide polymorphism (SNP) obtained by genotyping by sequencing method, CAScreen1.0 program compiled by MATLAB language was conducted to identify the elite SNP genotype associated with combining ability of quality traits in parents. Totally 35 elite SNP genotypes involving 22 genes (genotypes) were detected associated with GCA of seven quality traits (P < 0.05) in both 2014 and 2015. Seven and four SNPs were detected associated with combining ability for MRR and HRR, respectively. For PCG and CD, six and ten SNPs were detected associated with combining ability of parents, respectively. Six SNPs involving two genes were detected for combining ability of GC. Only two SNPs were detected which associated with combining ability for ASV. For combining ability of AC, six elite SNPs genotype were detected. Among them, elite SNP genotype of LOC_Os08g25220 (T/C) located on chromosome 8 could significantly reduce AC content in mixed rice samples of hybrid japonica rice.

Genome-Wide Association Study Using Historical Breeding Populations Discovers Genomic Regions Involved in High-Quality Rice.

Rice ( L.) is one of the most important staple food crops in the world; however, there has recently been a shift in consumer demand for higher grain quality. Therefore, understanding the genetic architecture of grain quality has become a key objective of rice breeding programs. Genome-wide association studies (GWAS) using large diversity panels have successfully identified genomic regions associated with complex traits in diverse crop species. Our main objective was to identify genomic regions associated with grain quality and to identify and characterize favorable haplotypes for selection. We used two locally adapted rice breeding populations and historical phenotypic data for three rice quality traits: yield after milling, percentage of head rice recovery, and percentage of chalky grain. We detected 22 putative quantitative trait loci (QTL) in the same genomic regions as starch synthesis, starch metabolism, and cell wall synthesis-related genes are found. Additionally, we found a genomic region on chromosome 6 in the population that was associated with all quality traits and we identified favorable haplotypes. Furthermore, this region is linked to the gene that codes for a starch branching enzyme I, which is implicated in starch granule formation. In , we also found two putative QTL linked to , , and . Our study provides an insight into the genetic basis of rice grain chalkiness, yield after milling, and head rice, identifying favorable haplotypes and molecular markers for selection in breeding programs.

Genetic Dissection of qPCG1 for a Quantitative Trait Locus for Percentage of Chalky Grain in Rice (Oryza sativa L.).

Rice is a pivotal cereal crop that provides the staple food for more than half of the world’s population. Along with improvements in the standard of living, people not only pay attention to the grain yield but also to the grain quality. Chalkiness is one of the most important index of grain quality. In this study, qPCG1, a QTL for percentage of chalky grain, was mapped in an interval with a physical distance about 139 kb on chromosome 1 by residual heterozygous line (RHL) method. qPCG1 was incomplete dominant and the additive effect plays a major role and explained 6.8–21.9% of phenotypic variance within the heterogeneous region on chromosome 1. The effect of allele from Zhonghui9308 was decreasing the percentage of chalky grains (PCG). Microscope observation results indicated that there are great differences in the shape, structure and arrangement of starch granule between the chalky part and transparent part. Analysis of starch physicochemical properties showed that the total starch content, amylose content and chain length distribution of amylopectin changed while the protein contents were not apparently affected with the changed chalkiness. qPCG1 had little influence on main agronomic traits and it might be useful in rice breeding for it did not bring negative effect on grain yield while reducing the chalkiness.

Validation and Fine Mapping a Multifunction Region qPCG10/qDC10 Conferring Chalkiness and Grain Shape of Rice

Chalkiness and grain shape are two important appearance traits of milled rice (Oryza sativa L.), and grain shape is generally considered to greatly affect chalkiness of endosperm. This study was conducted to validate and fine map an important multifunction region located on the long arm of rice chromosome 10, qPCG10/qDC10, conferring grain shape and chalkiness that has not been well characterized. The quantitative trait loci validations were first performed using BC2F2 and BC2F2:3 populations derived from indica maternal line Teqing and recurrent paternal line IR24. Plants with overlapping heterozygous segments in the interval of RM3773 to RM6673 were selected from the BC4F2 population to develop near‐isogenic lines for fine mapping of qPCG10/qDC10. Using two‐way ANOVA of phenotypic variance among three genotype groups in each near‐isogenic line set, qPCG10/qDC10 was delimited to a 93.4‐kb region flanked by RM25828 and RM3123 and showed significant effects on grain width, grain length, 1000‐grain weight, percentage of chalky grain, and degree of chalkiness. We speculated that the multifunction region may harbor a novel gene causing chalkiness and grain shape. The present study will facilitate the cloning of qPCG10/qDC10 and the exploration of the molecular mechanisms underlying rice grain chalkiness.

Physiological and genotype-specific factors associated with grain quality changes in rice exposed to high ozone

Rising tropospheric ozone concentrations in Asia affect the yield and quality of rice. This study investigated ozone-induced changes in rice grain quality in contrasting rice genotypes, and explored the associated physiological processes during the reproductive growth phase. The ozone sensitive variety Nipponbare and a breeding line (L81) containing two tolerance QTLs in Nipponbare background were exposed to 100 ppb ozone (8 h per day) or control conditions throughout their growth. Ozone affected grain chalkiness and protein concentration and composition. The percentage of chalky grains was significantly increased in Nipponbare but not in L81. Physiological measurements suggested that grain chalkiness was associated with a drop in foliar carbohydrate and nitrogen levels during grain filling, which was less pronounced in the tolerant L81. Grain total protein concentration was significantly increased in the ozone treatment, although the albumin fraction (water soluble protein) decreased. The increase in protein was more pronounced in L81, due to increases in the glutelin fraction in this genotype. Amino acids responded differently to the ozone treatment. Three essential amino acids (leucine, methionine and threonine) showed significant increases, while seven showed significant treatment by genotype interactions, mostly due to more positive responses in L81. The trend of increased grain protein was in contrast to foliar nitrogen levels, which were negatively affected by ozone. A negative correlation between grain protein and foliar nitrogen in ozone stress indicated that higher grain protein cannot be explained by a concentration effect in all tissues due to lower biomass production. Rather, ozone exposure affected the nitrogen distribution, as indicated by altered foliar activity of the enzymes involved in nitrogen metabolism, such as glutamine synthetase and glutamine-2-oxoglutarate aminotransferase. Our results demonstrate differential responses of grain quality to ozone due to the presence of tolerance QTL, and partly explain the underlying physiological processes.

Open-Top Chambers with Solar-Heated Air Introduction Tunnels for the High-Temperature Treatment of Paddy Fields

The quality of rice grain has been deteriorating as a result of the high temperature during the ripening stage caused by global warming. Easy and effective methods of high-temperature treatment are essential for the analysis of high-temperature tolerance and to screen for tolerant strains. We have improved the open-top chamber (OTC) by adding a solar-heated air introduction tunnel (SAT). The air is warmed by solar radiation as it passes through the tunnel and then flows into the OTC. The increase in temperature in the OTC-SAT was powered by solar radiation. Thereby, the temperature in OTC-SAT rose during the day according to the distance from the air intake (the nearer, the higher). A more uniform increase in temperature of approximately 1.2°C in the daytime was achieved by attaching a sloping wall and funnel-shaped air exhaust tunnel to the OTC-SAT to improve the air flow. The area of the high-temperature treatment was easily increased by increasing the width of the OTC-SAT; this finding might be useful for screening a large number of strains. The increase in the percentage of chalky grains by the use of OTC-SAT was similar to that obtained with the other treatment methods; the OTC-SAT will thus be useful for investigating high-temperature tolerance during the ripening stage, particularly in areas where the wind direction is stable. The use of an OTC with a funnel-shaped tunnel on both the air entrance and the air exit sides might be useful in areas where the wind direction is often reversed.

Effect of Drying on Physical Qualities and Sensory Evaluation of Herbal Germinated Brown Rice by Hot Air: Turmeric and Roselle

The object of this project was to study the effect of drying temperature on physical quality and sensory evaluation of germinated brown rice soaking with tumeric and roselle. The drying was run under the conditions of drying temperatures of 80-100°C and air velocity of 7.3 m/s. Initial moisture content of brown rice samples was of 54-55% dry-basis and was dried until the final moisture content reached to 20-25% dry-basis. After drying, the rice was tempered and then was ventilated by ambient air until its moisture content reached to 14-15% dry-basis. The experiment showed that highest drying rate is incident at 100°C. For physical qualities analysis, the results showed that the drying air temperature does not affect to head rice yield, fissured kernels, chalky grain and color (L*, a*, b* CIE-lab unit) of herbal germinated brown rice. In addition, herbal germinated brown rice drying can maintain low percentage of chalky grain compared to commercial brown rice. The soaking solution was not affect to drying rate. Finally, the sensory evaluation showed that the herbal germinated brown rice dried with all drying conditions was acceptable taste (&gt;5).

Quantitative Trait Loci for Grain Chalkiness and Endosperm Transparency Detected in Three Recombinant Inbred Line Populations of Indica Rice

Quantitative trait loci (QTL) for percentage of chalky grain, degree of chalkiness, and endosperm transparency were detected using 3 recombinant inbred line populations derived from crosses between parental lines of commercial three-line hybrids of indica rice. Two of the populations showed great variations on heading date, and the other had a short range of heading date variation. A total of 40 QTLs were detected and fell into 15 regions of 10 chromosomes, of which 5 regions were detected for 1 or more same traits over different populations, 2 were detected for different traits in different populations, 3 were detected for 2 or all the 3 traits in a single population, and 5 were detected for a single trait in a single population. Most of these QTLs have been reported previously, but a region located on the long arm of chromosome 10 showing significant effects in all the 3 populations has not been reported before. It was shown that a number of gene cloned, including the Wx and Alk for the physiochemical property of rice grain, and GW2, GS3 and GW5 for grain weight and grain size, could have played important roles for the genetic control of grain chalkiness in rice, but there are many more QTLs exerting stable effects for rice chalkiness over different genetic backgrounds. It is worth paying more attentions to these regions which harbor QTL such as the qPCG5.2/qDC5.2/qET5.2 and qPCG10/qDC10/qET10 detected in our study. Our results also showed that the use of segregating populations having high-uniform heading date could greatly increase the efficiency of the identification of QTL responsible for traits that are subjected to great environmental influence.

Effects of Growth Duration on Grain Yield and Quality in Rice (Oryza sativa L.)

It is important to clear the relationships of growth duration with rice yield and quality in determining the breeding ob-jectives and cultivation strategies. In this paper, plants of japonica rice varieties Ning 111 and Chunjiang 302 with different growth durations resulted from short-day treatment were used to investigate the changes of yield and rice quality. The results showed that, the growth duration of more than 152 d had little effect on yield, but when less than 152 d, there was a significant positive correlation between growth duration and yield or dry matter accumulation; the smallest length and width of rice, as well as the lowest protein content and setback of amylum were observed in the treatments G2 or G3, which had moderate growth dura-tion of 131–132 d, the growth duration more than or less than 131–132 d would both increase the values of these rice quality indi-ces; amylose content also showed a similar trend, and the minimum value in two species all appeared in treatment G3 (132 d or 137 d), while for breakdown of amylum, the trend was just opposite. The percentage of chalky grains, chalkiness and gelatiniza-tion temperature in two varieties rose with shortening growth duration; the effects of growth duration on milling quality were gen-erally lower.

Effects of Nitrogen Nutrition on Grain Quality in Upland Rice Zhonghan 3 and Paddy Rice Yangjing 9538 under Different Cultivation Methods

Upland rice and dry-cultivated paddy rice have been attracted more and more attention because of limited water re- sources in China. Researches on interaction between water and nitrogen supplies for crop resistance to drought stress has become a hot topic in crop physiology. However, the information linking to the effect of nitrogen nutrition on grain quality of upland rice and paddy rice under different cultivation methods is unavailable. The objective of this study was to evaluate the difference be- tween upland rice and paddy rice and interaction between cultivation methods and N levels. One upland rice cultivar Zhonghan 3 (japonica) and one paddy rice cultivar Yangjing 9538 (japonica) were grown under either moist cultivation (MC, control) or bare dry-cultivation (DC) conditions, with three N levels, low amount of nitrogen (LN, 100 kg ha-1), normal amount of nitrogen (NN, 100 kg ha-1), and high amount of nitrogen (HN, 300 kg ha-1). The results showed that, compared with NN, the grain yield under HN was lower for both upland and paddy rice under DC and for paddy rice under MC, whereas it was higher for upland rice under MC. Under both DC and MC, the percentage of chalky grains and the chalkiness of upland rice were increased under NN and reduced under HN. With the increase in N levels, amylose content was reduced and protein content was increased for both upland and paddy rice. However, the percentage of chalky grains and the chalkiness of paddy rice was decreased under DC and increased under MC. Breakdown viscosity was the highest and setback viscosity was the lowest for upland rice under NN and for paddy rice under LN. The bare dry cultivation can improve appearance quality and nutrient quality for upland rice. There was no significant difference in other rice quality indices between upland rice and paddy rice under DC. Compared with paddy rice, upland rice showed better nutrient quality and poor appearance quality and cooking quality. The correlation coefficient between cooking and nutrient quality and leaf nitrogen content was smaller for upland rice than for paddy rice. The results suggest that the response to cultivation methods and nitrogen levels varies largely between upland rice and paddy rice. The approaches to increase grain yield and grain quality for both paddy and upland rice were discussed.

Effects of Nitrogen Nutrition on Grain Quality in Upland Rice Zhonghan 3 and Paddy Rice Yangjing 9538 Under Different Cultivation Methods

For evaluating the differences between upland and paddy rice ( Oryza sativa L.) as well as interaction between cultivation methods and nitrogen (N) levels, the upland rice cultivar Zhonghan 3 ( japonica) and the paddy rice cultivar Yangjing 9538 ( japonica) were planted in moist cultivation (MC) and bare dry-cultivation (DC). Each cultivar had 3 N-application treatments (100 kg −1 for low N, 200 kg −1 for normal N, and 300 kg −1 for high N) in MC and DC conditions. Compared with normal N treatment, HN reduced grain yield for both cultivars under DC and for the paddy rice cultivar under MC; whereas, it promoted the yield of upland rice under MC. With the increase of N application rate, the percentage of chalky grain and the chalkiness of upland rice increased under DC, however, the 2 indices were the largest in the normal N treatment and the smallest in the high N treatment under MC; for paddy rice, the percentage of chalky grains and the chalkiness showed a declined trend under DC but an in increased trend under MC. Under both MC and DC, the protein content enhanced in both upland and paddy rice when more N was applied, whereas the amylose content declined. The highest breakdown viscosity and the lowest setback viscosity were observed in upland rice treated with normal N and in paddy rice treated with low N. Compared with MC, DC improved the appearance quality and the nutrient quality of upland rice, and there was no significant variations in other quality indices between upland and paddy rice. The upland rice had better nutrient quality but poorer appearance and cooking qualities than paddy rice. The cooking and nutrient qualities showed lower correlations to the leaf N content in upland rice than paddy rice. These results suggest that the response of upland rice to cultivation method and N level is in great difference to that of paddy rice.

QTL Mapping and QTL × Environment Interactions of Milling Quality and Percentage of Chalky Grain in Upland Rice Introgression Lines under Upland and Lowland Environments

Milling quality and percentage of chalky grain of rice(Oryza sativa L.) are important traits to producers and consumers.The objectives of this study were to characterize the response of brown rice(BR),milled rice(MR),head milled rice(HMR),and percentage of chalky grain(PCG) to upland water stress and to identify QTLs for the traits.A set of 271 introgression lines(ILs)(BC5F3),carrying segments from upland cultivar IRAT109 in the background of lowland rice cultivar Yuefu,were used,and data were collected under upland and lowland environments.Great changes were detected between upland and lowland conditions in head milled rice and percentage of chalky grain,but relative stability in brown rice and milled rice.Head milled rice increased and percentage of chalky grain significantly decreased under upland condition.A total of ten additive QTLs and two pairs of digenic epistatic interactions QTLs for BR,MR,HMR,and PCG were detected on chromosomes 3,4,7,8,and 9.The contribution of single QTL ranged from 1.81% to 17.49%,three QTLs(qMR9,qHMR7,qHMR9) and one pairs of digenic epistatic interactions(qHMR3-qHMR9) accounted for above 10% of the phenotypic variation.Six QTLs were no significant QTL×Environment interaction effects,seven QTLs were the same with those from previous reports,and two genomic intervals,RM1112-RM1272 on chromosome 4 and RM1189-RM410 on chromosome 9,were cluster regions of the QTLs.These co-localized QTLs and common QTLs will facilitate marker-assisted selection for grain quality traits in rice breeding.

Relationship Between Root Chemical Signals and Grain Quality of Rice

This study was designed to elucidate the relationship between root chemical signals and the quality of rice. Various rice genotypes were used. Zeatin (Z) + zeatin riboside (ZR), abscisic acid (ABA), 1-aminocylopropane -1-carboxylic acid (ACC), and organic acids in roots during grain filling and the appearance quality, cooking/eating quality were investigated. The correlations among them were analyzed. The results showed that Z + ZR concentrations in the roots at mid- and late-grain-filling stages were significantly and positively correlated with the gel consistency and alkali spreading value ( r = 0.72 * – 0.90 **), whereas negatively correlated with the amylose content ( r = −0.68 * – −0.78 **). ABA concentrations in roots at mid-grain-filling stage were significantly and negatively correlated with the gel consistency and alkali spreading value ( r = −0.90 ** – −0.91 **), and positively correlated with the amylose content ( r = 0.87 **). ACC concentrations in root exudates at mid-grain-filling stage were very significantly correlated with the percentage of chalky grains and chalkiness ( r = 0.97 ** − 0.98 **), and those at late-grain-filling stage were significantly correlated with chalkiness and chalky size ( r = 0.69 * −0.96 **). The more the malic acid and succinic acid exuded from roots for a cultivar, the greater the breakdown values and the smaller the setback values in the starch profile, and the results were reversed for a cultivar with more tartaric acid and citric acid exuded from roots during the grain-filling period. The cultivar with more lactic acid in exudates had smaller gel consistency and alkali spreading values, but had greater amylose content. When roots were treated with exogenous ZR, ABA, and ACC during grain filling, effects of the chemicals on the rice quality were consistent with the relationships of the endogenous hormones (Z + ZR, ABA, and ACC) with the quality indexes. Using rape cake as organic fertilizer can increase the concentrations of malic acid and succinic acids exuded from roots as well as the breakdown value in starch profile and reduce the setback value. The results suggest that root chemical signals play important roles in the formation of rice quality, and rice quality could be improved through regulating the signals.