() Relationship of Rice Grain Amylose, Gelatinization Temperature and Pasting The different sensory qualities of cooked rice could meet the .. needs to be matched for them to be successful and to be widely adopted. The purpose of this research was to assess the variation in grain quality traits . and broken rice site for successful exploitation of desirable traits refers to the. Abstract. Rice grain quality improvement has become very crucial for most breeding programs. around the world. Grain quality is a complex trait which comprises milling, appearance . has a direct in uence on marketability and success of commercial varieties. Cooking .. ences the relationship between PV and AAC .
The high linkage disequilibrium expected in rice lines and cultivars facilitates the detection of marker-trait associations for implementing marker assisted selection, and the mining of alleles related to important traits in germplasm.
It is already being successfully applied for identifying genes related to human diseases. Research in humans has turned to association analysis, since linkage analysis has not been successful in the fine-scale mapping of disease loci, due to the impossibility of undertaking controlled-breeding crosses Flint-Garcia et al. Unlike humans, in most plant species, the identification of those genomic regions which contribute to important characteristics has been mostly achieved through linkage analysis within segregating populations, the result of crosses between genitors with contrasting phenotypes and genotypes Buntjer et al.
In breeding and pre-breeding programs, QTL detection is an important tool for the identification of favorable alleles and for identifying and validating molecular assisted selection MAS. The identification of genomic regions related to quantitative traits in plants was largely achieved through QTL mapping Skot et al.
However, there are some inherent limitations to QTL analysis. First, in linkage studies, the segregating population usually presents only two segregating alleles per locus, which means that in any given cross, the sampled genetic diversity may be limited.
In addition, the potential use of the genetic diversity available in species is restricted Peleman and van der Voort, Another disadvantage as regards the substantiation of a low number of traits per cross, is through the difficulty in identifying parents with contrasting genotypes and phenotypes for all those traits of interest Buntjer et al. Furthermore, the high resolution desired for MAS or cloning candidate genes requires developing large segregating populations, possibly difficult in some species Skot et al.
According to Zondervan and Cardonthe main purpose in linkage analysis, as in association mapping, is the detection of correlations between phenotypic variation and genotypes through linkage disequilibrium. However, association analysis has the advantage of contemplating all the meiotic and recombination events that may occur in the evaluated population Ferreira and Grattapaglia, Furthermore, this form is highly dependent on the extent of linkage disequilibrium LDa higher degree implying the use of less markers per chromosome, without the loss of genetic resolution for marker assisted selection MAS Rostoks et al.
As rice is a self-pollinating species, it is expected to present high linkage disequilibrium Flint-Garcia et al. In addition, the recent bottlenecks encountered since the beginning of rice breeding have given rise to high linkage disequilibrium blocks, thereby facilitating association studies Patron et al. One of the great advantages of association mapping lies in the fact that no mapping population needs to be developed, as the sampling of non-related individuals represents a series of advantages towards developing and validating MAS in breeding programs Jannink et al.
Such a strategy, unlike traditional linkage analysis, facilitates the search for functional variation in a much broader germplasm context Zhu et al. Thus, experimental populations may constitute a representative sample of a larger population for which inferences are sought Breseghello and Sorrels, b.
In panels with highly divergent individuals and assumed random mating, only polymorphisms with extremely tight linkage to a locus with desirable phenotypic effects are likely to be significantly associated with a given trait Remington et al.
Furthermore, association analysis can benefit by including data collected over years of experimental analysis with genotypes of breeding programs, with the additional possibility of analyzing several traits simultaneously. Improving grain yield and quality are important challenges in rice breeding, thus priorities for the international market Fan et al. Although quality assumes many aspects and is highly related to preference in diverse cultures, its characteristics are mainly defined by milling properties, grain size and shape, cooking and eating characteristics, and nutritional qualities He et al.
According to He et al. The aims of this work were to analyze and identify the association of simple sequence repeat SSR markers with yield and grain quality traits in a panel of accessions from the Embrapa Rice Core Collection ERiCCrepresented by breeding material from Brazil and other countries.
Each accession was evaluated in a four-plant bulk, the total genomic DNA being extracted as described by Brondani et al. Data were taken from the two middle rows and the 4 central meters of each. Previous research investigated the relationship between morphological traits and grain quality [ 27 ], between mineral elements and other quality traits [ 2829 ], and between grain yield and physiological grain traits [ 30 ]. However, a full understanding of the possibility to produce high-yielding rice of good quality at stressful conditions, in particular drought, is still lacking.
The aim of this study was to characterize the variation in grain yield and its components and nutritional composition in a selection of Rwandan rice cultivars. The second aim of this study was therefore to understand the interplay between grain yield components and nutritional quality traits in these cultivars, thereby creating the basis for the breeding of high yielding and nutritionally beneficial cultivars for rice production in Rwanda.
Material and Methods 2. Plant Material Production characteristics for the seven rice cultivars used in this study, obtained from the College of Agriculture, Animal Science and Veterinary Medicine of the University of Rwanda, are presented in Table 1.
The remaining cultivars were released in The cultivars were selected because they were the most cultivated in Rwanda and their medium water requirements were as described by ISAR [ 32 ].
Growing Conditions in the Climate Chamber and Experimental Setup To allow proper comparison of characters among the rice cultivars, the impact of environmental effects was minimized through cultivation in a controlled environment.
Rice plants were grown in a climate chamber in the biotron facility of the Swedish University of Agricultural Sciences at Alnarp, Sweden. Pots were placed into big plastic trays capable to hold water. Potted soil was gently sprinkled with tap water before sowing. Two seeds per pot were directly sown into the wet soil at 1 to 2 cm depth.
After emergence, the seedlings were trimmed to one seedling per pot. The soil was regularly watered with tap water from soil surface until the seedlings were three weeks old. After three weeks, water was regularly added into the plastic trays, and plant roots had access to water through holes in the bottom of the pots. Fertilizer Application The plastic trays were arranged into two compartments, one for moderate fertilizer dose and the other for high fertilizer dose.
Each compartment contained five replicates per cultivar. The quantity of nitrogen to be applied per plant was calculated based on the fertilizer rate recommended by Manzoor et al. Universal blue water-soluble fertilizer NPK was used as the source of nutrients.
Fertilizer solution was gently sprinkled on the soil surface. The fertilization started three weeks after sowing and was weekly applied until flowering.
International Rice Research Institute - IRRI - Grain Quality and Nutrition Center
The fertilizer solution was applied at two different doses, and each plant was given either 0. Nutritional Content of Rice Grains 2. Samples were freeze-dried for 48 hours. The volume of cooled mixture was adjusted to ml by adding water. Total Phenolic Content Total phenolic content was determined following Singleton et al.
The mixture was then left for 75 minutes at room temperature. The optic density was determined using a Thermo Scientific Multiskan Go spectrophotometer at nm. Gallic acid was used as standard. Total phenolic content in rice samples was expressed as Gallic equivalent per g of dry sample.
The extraction was done in two steps. The supernatant was recuperated in a new tube. The supernatant second extract was added to the first extract. For the assay, a reagent was prepared by mixing mM acetate buffer pH 3. FeSO4 7H2O was used as standard solution. Amount and Size Distribution of Polymeric and Monomeric Protein Amount and size distribution of polymeric and monomeric proteins was evaluated by size-exclusion high-performance liquid chromatography SE-HPLC according to Johansson et al.
Proteins were extracted from rice sample flour in triplicates. Available proteins were first extracted in a buffer including 0.
Journal of Food Quality
A mixture of 20 mg flour sample and 1. The supernatant was transferred into a new vial. A total of 1. The second extract was transferred to a new different vial. Statistical Analysis Statistical analysis was carried out using the Minitab 16 software.
In order to determine the relationships among characteristics as well as similarities and differences among analysed cultivars, principal components analysis was applied. Results and Discussion 3. Results Two of the cultivars, that is, Intsindagirabigega and Zong geng, failed to flower at the higher fertilizer dose and did not produce grains for nutritional analysis.
Therefore, data from the cultivation at moderate fertilizer dose of Intsindagirabigega and Zong geng are included in tables to contribute with options for comparison.
Mineral Content Mean values for each of the minerals analysed, for each of the cultivars, and at each of the fertilizer doses are available in the supplementary data Table S1.
Significant differences were found among both cultivars and between plants grown at different fertilizer doses for mineral content and composition Table 2. Three cultivars were shown in this study to be more mineral dense than the other evaluated cultivars: The moderate fertilizer dose resulted in higher contents of Fe, Ca, and Ba in rice grains than the high fertilizer dose, while contents of Zn, K, P, Na, and S were significantly higher in grains of plants fertilized with the high dose Table 2.
Heavy Metal Content Mean values for each of the heavy metals analysed, for each of the cultivars, and at each of the fertilizer doses are available in the supplementary data Table S2.
Significant differences were recorded among cultivars and fertilizer doses for heavy metal content in the grains Table 3. Low contents of heavy metals were found in the cultivars Mpembuke especially of Cd and Cr and Ndamirabahinzi especially of As and Cowhile high contents were found in the cultivars Ingwizabukungu Co and Cr and Jyambere As and Cd.
The high fertilizer dose resulted in higher contents of Cd and Pb in the rice grains than the moderate fertilizer dose Table 3. Bioactive Compounds in Grains Mean values for total phenolic content TPC and total antioxidant capacity TACfor each of the cultivars, and at each of the fertilizer doses are available in the supplementary data Table S3.
Mean values for the different analysed protein fractions see Materials and Methods for descriptionfor each of the cultivars, and at each of the fertilizer doses are available in the supplementary data Table S4. In all cultivars, the percentage of total extractable proteins was higher for the slow-eluting fraction peak 4 and 5. P1—P5 shows the different peaks referred to in Table 6 and in the text.
Amount and size distribution of polymeric and monomeric protein in Rwandan rice cultivars. Yield-Related Traits and Grain Yield Mean values for yield and related traits, for each of the cultivars, and at each of the fertilizer doses are available in the supplementary data Table S5.
The high fertilizer dose 0. However, the results in the biotron may largely differ from the grain yield in the field because there are many environmental factors interacting with the treatments under studies and may cause great yield variations in the field.
Association mapping for yield and grain quality traits in rice (Oryza sativa L.)
Yield and yield component variation between rice cultivars and fertilizer doses. Thus, the cultivar Ndamirabahinzi showed the highest stability for all evaluated characters combined over the fertilizer doses applied. Furthermore, the high values of yield components including grain yield and Fe attributed to the cultivar Jyambere Tables 2 and 3 could mainly be annotated to the moderate fertilizer dose these parameters are found with positive PC2 values, as is Jyambere with the moderate fertilizer dose.
Similarly, the high values of Ca, K, Na, P, S, and Cd of the same cultivar Tables 3 and 4 could mainly be annotated to the high fertilizer dose Figure 2.
The cultivars Ingwizabukungu and Nemeyubutaka with moderate fertilizer dose were shown by the PCA to combine in the best way high yield with high Fe and Zn content, although showing low levels of bioactive components Figure 2. Loading a and score b plot from principal components analysis of grain yield, its components, mineral elements, total phenolic content, total antioxidant capacity, polymeric protein, protein solubility, and UPP.
Discussion To our knowledge, our study is the first to characterize the Rwandan rice cultivars for the combination of their grain yield attributes their nutritional value of minerals and bioactive compounds as well as their dough mixing properties.
So far, efforts in rice production in Rwanda have been focused on improving the productivity level and postharvest processing [ 47 ]. This study clearly grouped Rwandan-grown cultivars into two nutritionally distinct clusters: