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Journal of Food Quality
Volume 2018, Article ID 5134569, 12 pages
Research Article

Quality and Grain Yield Attributes of Rwandan Rice (Oryza sativa L.) Cultivars Grown in a Biotron Applying Two NPK Levels

1Department of Plant Breeding, Swedish University of Agricultural Sciences, P.O. Box 101, 23053 Alnarp, Sweden
2College of Agriculture, Animal Sciences and Veterinary Medicine, University of Rwanda, P.O. Box 210, Ruhengeri, Rwanda

Correspondence should be addressed to Alphonsine Mukamuhirwa; es.uls@awrihumakum.enisnohpla

Received 28 February 2018; Accepted 20 May 2018; Published 24 June 2018

Academic Editor: Eduardo Puértolas

Copyright © 2018 Alphonsine Mukamuhirwa et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


High-yielding rice cultivars with good processing quality and rich in nutrition suitable to a changing climate are of particular importance for future rice-based food production. Here, seven Rwandan rice cultivars were grown in a climate chamber of the biotron facility at the Swedish University of Agricultural Sciences, to be evaluated for their grain yield, nutritional composition, and dough mixing properties. Two different levels of inorganic fertilizer were applied weekly from the seedling stage until flowering. Significant differences for grain yield and quality attributes were found between cultivars. Jyambere showed significantly the highest yield while Ingwizabukungu, Nemeyubutaka, and Jyambere were high in mineral elements content. Ndamirabahinzi and Mpembuke had the highest levels of TPC and TAC. Generally, the lower fertilizer dose resulted in a better performance of the cultivars for both yield and quality attributes. Significantly higher content of Fe, Ca, and Ba was found in grains from the moderate fertilizer dose, whereas K, Na, P, S, Zn, Cd, and Pb increased in grains from the higher fertilizer dose. The cultivar Ndamirabahinzi showed less variability of evaluated characters across fertilizer doses. The results from this study may be used for rice breeding of cultivars with high yield and good grain quality.

1. Introduction

Rice (Oryza sativa L.) is one among the leading cereal staple foods together with wheat and maize [1]. Grain yield has been steadily increasing since the 1940s due to breeding efforts focusing on high-yielding cultivars and on improvements in crop husbandry [2, 3]. Quality of rice is of increasing interest. Four traits are recognised as the most important for rice quality: grain appearance, milling properties, eating and cooking qualities (ECQs), and nutritional composition [4]. Grain appearance refers to length, width, and chalkiness of grains. ECQs are mainly influenced by starch, amylose content, gel consistency, and gelatinization temperature [5]. However, protein content and composition in the rice grain also contribute to ECQs, besides being an important part of the nutritional composition of the grain [69]. Furthermore, the storage protein content and composition determine the flour quality and its dough mixing properties, for example, the dough development time, peak time, peak height, and loaf volume [1012]. Phytochemical compounds such as phenolic acids, flavonoids, and tannins are potential antioxidants. Polyphenols contribute to plant protection and have human health promoting properties, including being anticarcinogenic and having antimicrobial effects, and also they are known for their reduction of cardiovascular diseases [13, 14]. Correlations have been reported among content of specific mineral elements and ECQs for rice [15]. Until now, physical appearance and ECQs, both contributing to the commercial value of the product through consumer evaluations, have received a higher attention as compared to other quality traits [16].

Quality traits vary largely among rice cultivars, thereby indicating the presence of a strong genetic component in their determination [1720]. Rice grain quality traits are also influenced by environmental factors such as the soil status, fertilizer applications, and climate variations [21]. Nitrogen applications appear to be positively correlated with protein content [2224], while negatively with amylose content [9]. Potassium fertilization increases grain protein content without affecting gelatinization temperature and amylose content [25]. Significant genotype × environment interactions have been noted for protein content [25], heavy metals [26], and mineral elements [27].

The increasing world population calls for an enhanced food production, but adverse environmental and climate conditions may lead to great difficulties in achieving this goal. Hence, there is an increasing need to breed nutritional, high-yielding, and high-quality genotypes, adapted to stressful environments of various types. For success, relationships among traits such as grain yield, quality, nutrient content, and stress adaptation must be studied in detail. Previous research investigated the relationship between morphological traits and grain quality [27], between mineral elements and other quality traits [28, 29], 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.

2. Material and Methods

2.1. 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 rice cultivars have been released by the Agricultural Research Institute of Rwanda (ISAR), now known as the Rwanda Agricultural Board (RAB). The cultivar Zong geng commonly called “Kigoli” was introduced from China in the 1960s [31], while Intsindagirabigega was introduced in 2002 from WARDA (currently, Africa Rice Centre) and released in 2004. The remaining cultivars were released in 2010. The cultivars were selected because they were the most cultivated in Rwanda and their medium water requirements were as described by ISAR [32].

Table 1: Characteristics of 7 Rwandan rice cultivars (ISAR 2010).
2.2. 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. The day/night temperature was set to 30°C and 25°C, respectively, according to Wopereis [33], with 11 hours of light and 13 hours of darkness [34, 35]. Light intensity of 350 PAR µmol·s−1 was chosen following Hubbart et al. [36]. The atmospheric relative humidity was 70% according to Hirai et al. [37].

2.2.1. Soil Potting and Sowing

Pots with the size 6 × 10 × 12 cm were filled with soil. The soil composition was (g·m−3) 180, 90, 195, 260, 1000, 2000, 6, 3.5, 2.5, 1.5, 0.5, and 3 for N, P, K, Mg, S, Ca, Fe, Mn, Cu, Zn, B, and Mo, respectively. 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.

2.2.2. 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. [38]. Universal blue water-soluble fertilizer 18-11-18 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. The fertilizer solution was applied at two different doses, and each plant was given either 0.127 g·plant−1 (0.023 g·N, moderate dose) or 0.255 g·plant−1 (0.046 g·N, high dose).

2.3. Grain Yield Attributes

The number of tillers plant−1, number of fertile tillers plant−1, spike length, and number of spikelets spike−1 were measured at harvesting time following the rice standard evaluation system [39]. The grains were threshed by hand, and grain yield plant−1 was measured using a precision balance.

2.4. Nutritional Content of Rice Grains
2.4.1. Sample Preparation

Rice grains harvested per cultivar and per fertilizer dose were pooled and stored at −20°C. Samples were freeze-dried for 48 hours. Dry samples were grinded to fine flour using IKA- WERKE grinder type A10 (Skafte MedLab, Germany). The flour was kept at −20°C until further analyses.

2.4.2. Determination of Mineral Elements and Heavy Metal Content

A mixture of 500 mg lyophilised flour sample and 10 ml of HNO3 in two replicates was combusted at 185°C for 17 minutes. The volume of cooled mixture was adjusted to 100 ml by adding water. The analyses of minerals and heavy metal content were made using an ICP-OES, Optima 8300, and PerkinElmer [40] at Lund University following methods described in [41, 42].

2.4.3. Total Phenolic Content

Total phenolic content was determined following Singleton et al. [43] with minor modifications. Total phenolic compounds were extracted from lyophilised flour sample in triplicate using 70% ethanol, 1% HCl, and sonication for 1 hour. The extract was centrifuged at 8000 g·min−1 for 10 min, and the supernatant was recuperated into a new tube. Sixty-microliters of extract and 60 µl of Folin–Ciocalteu reagent were added to 250 µl of water. The samples were left to react for 6 min before adding 600 µl of 7% Na2CO3 per sample. The mixture was then left for 75 minutes at room temperature. The optic density was determined using a Thermo Scientific Multiskan Go spectrophotometer at 650 nm. Gallic acid was used as standard. Total phenolic content in rice samples was expressed as Gallic equivalent per 100 g of dry sample.

2.4.4. Determination of Total Antioxidant Capacity

The total antioxidant capacity was determined following the method of Pérez-Jiménez and Saura-Calixto [44] with slight modifications. 50 mg of flour was measured from each sample in triplicate. The extraction was done in two steps. In the first step, 1 ml of 50% methanol, pH 2, was added to the flour sample. The mixture was shaken at 1000 g·m−1 for 1 hour at room temperature and then centrifuged at 8000 g·min−1 for 10 minutes. The supernatant was recuperated in a new tube. 70% acetone was added to the pellet and then shaken and centrifuged as described above. The supernatant (second extract) was added to the first extract. For the assay, a reagent was prepared by mixing 300 mM acetate buffer (pH 3.6), 10 mM of 2,4,6-tripyridyl-s-triazine (TPTZ) in 40 mM HCl, and 20 mM FeCl3·6H2O in a 10 : 1 : 1 ratio. FeSO4 7H2O was used as standard solution. About 200 µl of fresh reagent was added to 20 µl of sample extract or standard solution in a 96-well plate. The plate was heated at 37°C for 30 minutes in a microwave oven, and the absorbance was measured using the Thermo Scientific Multiskan Go spectrophotometer at 593 nm. Total antioxidant capacity was expressed in µmol Fe2+ equivalent per gram of the sample’s dry weight.

2.4.5. 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. [45]. Proteins were extracted from rice sample flour in triplicates. Available proteins were first extracted in a buffer including 0.5% SDS + 0.05 M NaH2PO4 (pH 6.9). A mixture of 20 mg flour sample and 1.4 ml buffer was shaken at 2000 g·m−1 for 5 minutes and then centrifuged at 10000 g·m−1 for 30 minutes. The supernatant was transferred into a new vial. A total of 1.4 ml of buffer was added to the pellet remaining from the first extraction and SDS-non-extractable proteins were extracted by ultrasonication for 45 seconds and then centrifuged as described above. The second extract was transferred to a new different vial. The percentage of total polymeric proteins and polymeric proteins that are present in an unextractable form (%UPP) was determined according to Gupta et al. [46], and percentage solubility of rice flour proteins was calculated as proposed by Oszvald et al. [11].

2.5. Statistical Analysis

Statistical analysis was carried out using the Minitab 16 software. The analysis of variance was done by general linear model (GLM) analyses, whereas Tukey’s method was used for mean comparisons. In order to determine the relationships among characteristics as well as similarities and differences among analysed cultivars, principal components analysis was applied.

3. Results and Discussion

3.1. 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.

3.1.1. 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: Ingwizabukungu being high in Fe, Mg, P, and Zn, Jyambere being high in Ca, Fe, K, Mg, P, and S, and Nemeyubutaka being high in Fe, Mg, Mn, P, and Zn. 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).

Table 2: Mean mineral element content (mg·kg−1 dry weight) (102) in Rwandan rice cultivars.
3.1.2. 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 Co), while 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).

Table 3: Heavy metal content (mg·kg−1 dry weight) (10) in Rwandan rice cultivars.
3.1.3. Bioactive Compounds in Grains

Mean values for total phenolic content (TPC) and total antioxidant capacity (TAC), for each of the cultivars, and at each of the fertilizer doses are available in the supplementary data (Table S3). Significant differences were observed between cultivars for TPC and TAC (Table 4). A strong positive correlation () was found between TPC and TAC. The cultivar Ndamirabahinzi had the highest TPC and TAC.

Table 4: Total phenolic content (TPC) and total antioxidant capacity (TAC) in Rwandan rice cultivars.
3.1.4. Amount and Size Distribution of Polymeric and Monomeric Protein

Figure 1 shows representative SE-HPLC chromatograms from the cultivar Mpembuke, which are subdivided into five fractions based on retention time. Protein fractions eluting fast (elution time < 17 minutes; peak 1, 2, and 3) were designated as high molecular weight proteins while those with slow elution (elution time > 17 minutes; peak 4 and 5) were designated as low molecular weight proteins. Mean values for the different analysed protein fractions (see Materials and Methods for description), for each of the cultivars, and at each of the fertilizer doses are available in the supplementary data (Table S4). Significant differences were found among the cultivars for solubility, %UPP, and total extractable proteins, whereas percentage of polymeric proteins was not found to differ significantly (Table 5). High protein solubility was recorded for Jyambere and Mpembuke, while Ingwizabukungu, Ndamirabahinzi, and Nemeyubutaka showed high %UPP. In all cultivars, the percentage of total extractable proteins was higher for the slow-eluting fraction (peak 4 and 5). This suggests that the largest proportion (>50%) of proteins in these cultivars is of low molecular weight.

Figure 1: The SE-HPLC profile of the protein content in Mpembuke grain: first extraction (a) and second extraction (b). P1–P5 shows the different peaks referred to in Table 6 and in the text.
Table 5: Amount and size distribution of polymeric and monomeric protein in Rwandan rice cultivars.
3.1.5. 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). Significant differences were recorded among the cultivars for all characters except fertile tillers plant−1 (Table 6). The cultivar “Jyambere” had the highest yield among the cultivars and also showed a high number of tillers plant−1 and fertile tillers, long spikes, and the highest number of spikelets spike−1. The cultivar “Zong geng” had tall plants (139 cm on average) but a low number of tillers plant−1. Significant differences in characters were also observed between the two fertilizer doses, except for the number of tillers plant−1 and spike length (Table 6). The high fertilizer dose (0.255 g·plant−1) resulted in taller plants as compared to the low fertilizer dose (0.127 g·plant−1). A higher number of productive tillers plant−1, higher number of spikelets spike−1, and higher grain yield were noted at the moderate dose. Extrapolated to yield ha−1, the grain yield varied between 5.2 for Mpembuke and Ingwizabukungu and 14.5 t·ha −1 for Jyambere. 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.

Table 6: Yield and yield component variation between rice cultivars and fertilizer doses.
3.1.6. Principal Components Analysis between Grain Yield, Its Components, and Nutritional Content

The PCA showed that PC1 (explaining 32% of the variation) values increased and PC2 (explaining 19.9% of the variation) values decreased with the increased fertilizer dose for all evaluated cultivars (Figure 2), with the largest change for Jyambere and the least change for Ndamirabahinzi. 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).

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. First principal component explained 32% of the variation while the second principal component explained 19.9% of the variation.
3.2. 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: a group of bioactive compound-rich cultivars formed by Ndamirabahinzi and Mpembuke, while Ingwizabukungu, Jyambere, and Nemeyubutaka were more preeminent in mineral elements. The cultivar Ingwizabukungu, Ndamirabahinzi, and Nemeyubutaka exhibited high %UPP, thus indicating high dough mixing strength.

The most mineral dense cultivars Ingwizabukungu, Jyambere, and Nemeyubutaka showed mineral levels similar to or higher than those reported by previous research [4850]. Despite the relatively high mineral content in these cultivars, the content of Ca, Zn, and Fe in 100 g DW rice was below the content recommended as daily intake [51]. Mineral content in rice cultivars of the present study correlated positively with heavy metal content in these cultivars, meaning that mineral dense cultivars were also the most heavy metal dense cultivars. However, none of the evaluated cultivars showed levels above the maximum tolerable limit for humans [52]. Furthermore, the content of heavy metals in the rice grains was similar to/or lower than contents reported by previous research [25, 5355].

In the present study, variation in phytochemical compounds was measured as content of TPC and TAC, being examples of quick and cheap methods being able to characterize such variations. To understand the full variation in phytochemicals in the evaluated rice cultivars, more sophisticated and expensive HPLC methods are a requirement. Our study confirmed the existence of a strong positive relation between phenolic compounds and antioxidant capacity, also reported by other researches [56, 57]. Bergman and Goffman [58] argued that phenolic compounds are the main factors of the antioxidant activity of rice grains. In fact, the chemical structure of both polyphenols [59] and their metal chelation potential [60] makes them powerful antioxidants. Moreover, some phenolic compounds play a role in stimulating antioxidant enzymes [61] or inducing antioxidant protein synthesis [62]. Shao et al. [63] hypothesized that the strong correlation between bioactive compounds may result from pleiotropy or genetic linkage between these traits. Phenolic compounds have been reported to play a role in plant defence and to have human health promoting benefits such as prevention of cardiovascular diseases and cancer [64]. The high content of TPC and TAC in the cultivar Ndamirabahinzi makes this cultivar a good candidate to be used in breeding for increased content of bioactive compounds in rice.

Rwandan cultivars exhibited a high proportion of low molecular weight proteins which is attributable to the evaluation of whole rice grain in this study. According to Van der Borght et al. [65], the fast eluting fraction contains α- and β-glutelin subunits, which are contributing to the mixing properties of the rice flour. The studied cultivars showed variation in solubility of the proteins and in the content of %UPP indicating differences in processing properties of the cultivars [11]. The slower eluting fraction in the SE-HPLC-based method is known to contain monomeric albumins, globulins, and prolamins, also being more soluble than the glutelin proteins [11]. The glutelins and prolamins are present in the endosperm of the rice seed while the albumins and globulins are dominating in the aleurone and the embryo, and as the latter are also richer in lysine, they are more nutritionally valuable than the glutelins and prolamins [66]. However, the aleurone and the embryo are removed by polishing. Thus, brown rice has the advantage over white rice for available nutrients in the grain especially those located in the aleurone and the embryo [67].

The moderate fertilizer dose was optimal for combining opportunities to produce high-grain yield and of nutritional quality for all cultivars, although the effect was more pronounced in some cultivars. Yu et al. [68] observed that grain content of N, P, and K increased with an increasing nitrogen supply up to 270 kg·hm−2 but decreased above this dose. Furthermore, excessive nitrogen fertilization was associated with a reduction in antioxidant capacity in wheat grains [69]. Nguyen and Niemeyer [70] reported a reduction of phenolic acids content and antioxidant capacity in basil at a high rate of nitrogen fertilizer. An increase in total phenolic content was observed with an increased dose of K fertilization but not with an increased dose of N fertilizer in Ziziphus jujube and apricot fruit [71, 72].

In the present study, the rice cultivation was carried out in a biotron, and despite mimicking the Rwandan climate, it is well known that results from a biotron are not fully comparable with those that will be obtained by field cultivation. Controlled growth in a climate chamber differs towards field cultivations in, for example, space in the soil for the roots, soil microbiota, and in abiotic and biotic stresses available in the field not present in the climate chamber. However, the present study presents the first characterization of Rwandan rice cultivars and their combined variation in grain yield components and nutritional quality. Thus, the results from this study may serve as a basis for selection and breeding of rice cultivars for increasing both grain yield and nutritional quality, and for further field selections within the material.

4. Conclusion

Potential uses in rice breeding for different purposes and end-uses varied among Rwandan rice cultivars. Generally, the low fertilizer dose was favourable for production of the majority of the rice cultivars in the biotron. Ndamirabahinzi may be included in crossbreeding for high phenolic content and antioxidant capacity, whereas Jyambere, Nemeyubutaka and Ingwizabukungu may be considered for the combined improvement of mineral element content and grain yield. Special care should be taken, however, to increase micronutrient content such as Zn and Fe in Rwandan rice cultivars.

Data Availability

The authors will make the raw data available upon request, which should be addressed to the corresponding author.

Conflicts of Interest

The authors have no conflicts of interest to declare.


Lund University is recognised for its collaboration in analysing mineral elements and heavy metals. The authors’ sincere gratitude goes to Maria Luisa Prieto-Linde (SLU) for her technical assistance. This research was funded by the Swedish International Development Cooperation Agency (SIDA) through research program cooperation between University of Rwanda and SLU.

Supplementary Materials

This supplementary material presents the “raw” data as mean values of each of the characters analysed to allow interested readers the opportunity to compare data in between fertilizer levels for each of the cultivars separately. (Supplementary Materials)


  1. D. Saikia and S. C. Deka, “Cereals: from staple food to nutraceuticals,” International Food Research Journal, vol. 18, pp. 21–30, 2011. View at Google Scholar
  2. S. Peng, K. G. Cassman, S. Virmani, J. Sheehy, and G. Khush, “Yield potential trends of tropical rice since the release of IR8 and the challenge of increasing rice yield potential,” Crop Science, vol. 39, pp. 1552–1559, 1999. View at Publisher · View at Google Scholar
  3. E. P. Guimarães, “Rice breeding,” in Handbook of Plant Breeding: Cereals, M. J. Carena, Ed., pp. 99–126, Springer Sciences Publishing, Berlin, Germany, 2009. View at Google Scholar
  4. P. He, S. G. Li, Q. Qian et al., “Genetic analysis of rice grain quality,” Theorical Applied Genetics, vol. 98, no. 3, pp. 502–508, 1999. View at Publisher · View at Google Scholar · View at Scopus
  5. Y. He, Y. Han, L. Jiang, C. Xu, J. Lu, and M. Xu, “Functional analysis of starch synthesis genes in determining rice eating and cooking qualities,” Molecular Breeding, vol. 18, no. 4, pp. 277–290, 2006. View at Publisher · View at Google Scholar · View at Scopus
  6. V. Derycke, W. S. Veraverbeke, G. E. Vandeputte, W. DeMan, R. C. Hoseney, and J. A. Delcour, “Impact of proteins on pasting and cooking properties of non-parboiled and parboiled rice,” Cereal Chemistry, vol. 82, pp. 468–474, 2005. View at Publisher · View at Google Scholar · View at Scopus
  7. T. Yu, W. Jiang, T. Ham et al., “Comparison of grain quality traits between japonica rice cultivars from Korea and Yunnan Province of China,” Journal of Crop Science and Biotechnology, vol. 11, no. 2, pp. 135–140, 2008. View at Google Scholar
  8. N. Singh, N. Pal, G. Mahajan, S. Singh, and K. Shevkani, “Rice grain and starch properties: effects of nitrogen fertilizer application,” Carbohydrate Polymers, vol. 86, no. 1, pp. 219–225, 2011. View at Publisher · View at Google Scholar · View at Scopus
  9. B. Peng, H. Kong, Y. Li et al., “OsAAP6 functions as an important regulator of grain protein content and nutritional quality in rice,” Nature Communications, vol. 5, no. 1, p. 4847, 2014. View at Publisher · View at Google Scholar · View at Scopus
  10. E. Johansson, M. L. Prieto-Linde, and J. Ö. Jönsson, “Effects of wheat cultivar and nitrogen application on storage protein composition and breadmaking quality,” Cereal Chemistry, vol. 78, no. 1, pp. 19–25, 2000. View at Google Scholar
  11. M. E. Oszvald, S. Tömösközi, O. Larroque, E. Keresztényi, L. Tamás, and F. Békés, “Characterization of rice storage proteins by SE-HPLC and micro z-arm mixer,” Journal of Cereal Science, vol. 48, no. 1, pp. 68–76, 2008. View at Publisher · View at Google Scholar · View at Scopus
  12. M. Wang, A. R. Tweed, and G. Carson, “How dough mixing properties affect bread-making performance,” in Proceedings of AACC International Annual Meeting, Honolulu, Hawaii, USA, September 2008.
  13. A. Bhattacharya, P. Sood, and V. Citovsky, “The roles of plant phenolics in defence and communication during Agrobacterium and Rhizobium infection,” Molecular Plant Pathology, vol. 11, no. 5, pp. 705–719, 2010. View at Google Scholar
  14. A. K. Dutta, P. S. Gope, S. Banik, S. Makhnoon, M. A. Siddiquee, and Y. Kabir, “Antioxidant properties of ten high yielding rice varieties of Bangladesh,” Asian Pacific Journal of Tropical Biomedicine, vol. 12, pp. 99–103, 2012. View at Google Scholar
  15. S. L. Jiang, J. G. Wu, Y. Feng, X. E. Yang, and C. H. Shi, “Correlation analysis of mineral element contents and quality traits in milled rice (Oryza sativa L.),” Journal of Agricultural Food Chemistry, vol. 55, no. 23, pp. 9608–9613, 2007. View at Publisher · View at Google Scholar · View at Scopus
  16. Y. Yu, R. A. Wing, and J. Li, “Grain quality,” in Genetics and Genomics of Rice, Plant Genetics and Genomics: Crops and Models, Q. Zhang and R. A. Wing, Eds., vol. 5, pp. 237–254, 2013. View at Google Scholar
  17. E. Adu-Kwarteng, W. O. Ellis, I. Oduro, and J. T. Manful, “Rice grain quality: a comparison of local varieties with new varieties under study in Ghana,” Food Control, vol. 14, no. 7, pp. 507–514, 2003. View at Publisher · View at Google Scholar · View at Scopus
  18. F. M. Anjum, I. Pasha, M. A. Bugti, and M. S. Butt, “Mineral composition of different rice varieties and their milling fractions,” Journal of Agricultural Science, vol. 44, no. 2, pp. 332–336, 2007. View at Google Scholar
  19. V. Vidal, B. Pons, J. Brunnschweiler, S. Handschin, X. Rouau, and C. Mestres, “Cooking behavior of rice in relation to kernel physicochemical and structural properties,” Journal of Agricultural and Food Chemistry, vol. 55, no. 2, pp. 336–346, 2007. View at Publisher · View at Google Scholar · View at Scopus
  20. Y. Chen, M. Wang, and P. B. F. Ouwerker, “Molecular and environmental factors determining grain quality in rice,” Food Energy Security, vol. 1, no. 2, pp. 111–132, 2012. View at Publisher · View at Google Scholar · View at Scopus
  21. R. M. Patrick and F. H. Hoskins, “Protein and amino acid content of rice as affected by application of nitrogen fertilizer,” Cereal Chemistry, vol. 51, no. 5, pp. 84–95, 1974. View at Google Scholar
  22. C. M. Perez, B. O. Juliano, S. P. Liboon, J. M. Alcantara, and K. G. Cassman, “Effects of late nitrogen fertilizer application on head rice yield, protein content, and grain quality of rice,” Cereal Chemistry, vol. 73, no. 5, pp. 556–560, 1996. View at Google Scholar
  23. T. M. Todorov, “Rice yield and its biological value of protein fertilized with an increased rate of mineral fertilizers,” Cahiers Options Méditerranéennes, vol. 15, pp. 65–70, 1996. View at Google Scholar
  24. M. A. Bahmaniar and G. A. Ranjbar, “Response of rice (Oryza sativa L.) cooking quality properties to nitrogen and potassium application,” Pakistan Journal of Biological Sciences, vol. 10, no. 11, pp. 1880–1884, 2007. View at Publisher · View at Google Scholar
  25. W. Cheng, G. Zhang, H. Yao, W. Wu, and M. Xu, “Genotypic and environmental variation in cadmium, chromium, arsenic, nickel, and lead concentrations in rice grains,” Journal of Zhejiang University Science B, vol. 7, no. 7, pp. 565–571, 2006. View at Publisher · View at Google Scholar · View at Scopus
  26. Y. Huang, C. Tong, F. Xu, Y. Chen, C. Zhang, and J. Bao, “Variation in mineral elements in grains of 20 brown rice accessions in two environments,” Food Chemistry, vol. 192, pp. 873–878, 2016. View at Publisher · View at Google Scholar · View at Scopus
  27. S. D. Koutroubas, F. Mazzini, B. Pons, and D. A. Ntanos, “Grain quality variation and relationships with morpho-physiological traits in rice (Oryza sativa L.) genetic resources in Europe,” Field Crops Research, vol. 86, no. 2, pp. 115–130, 2004. View at Publisher · View at Google Scholar · View at Scopus
  28. Y. W. Zeng, S. Q. Shen, L. X. Wang et al., “Correlation of plant morphological and grain quality traits with mineral element contents in Yunnan rice,” Rice Science, vol. 12, no. 2, pp. 101–106, 2005. View at Google Scholar
  29. P. Ngamdee, U. Wichai, and S. Jiamyangyuen, “Correlation between phytochemical and mineral contents and antioxidant activity of black glutinous rice bran, and its potential chemopreventive property,” Food Technology and Biotechnology, vol. 54, no. 3, pp. 282–289, 2016. View at Publisher · View at Google Scholar · View at Scopus
  30. Q. Xu, W. Chen, and Z. Xu, “Relationship between grain yield and quality in rice germplasm grown across different growing areas,” Breeding Science, vol. 65, pp. 3226–3232, 2015. View at Publisher · View at Google Scholar · View at Scopus
  31. Promar, Agriculture, Forestry and Fisheries of Rwanda. Fact-Finding Survey for the Support of Aid to Developing Countries (Fiscal Year 2011 Research Project), Ministry of Agriculture, Forestry and Fisheries, Tokyo, Japan, 2012.
  32. ISAR, Description of New Rice Varieties Introduced in Rwanda, Rwanda Agricultural Research Institute, Kigali, Rwanda, 2010.
  33. M. C. S. Wopereis, T. Defoer, P. Idinoba, S. Diack, and M. J. Dugué, Participatory Learning and Action Research (PLAR) for Integrated Rice Management (IRM) in Inland Valleys of Sub-Saharan Africa: Technical Manual, vol. 128, WARDA Training Series, Africa Rice Center, Cotonou, Benin, 2008.
  34. R. Best, Some Aspects of Photoperiodism in Rice (Oryza sativa L.), Elsevier, Amsterdam, Netherlands, 1961.
  35. B. S. Vergara and T. T. Chang, The Flowering Response of the Rice Plant to Photoperiod, IRRI, Manila, Philippines, 4th edition, 1985.
  36. S. Hubbart, S. Peng, P. Horton, Y. Chen, and E. H. Murchie, “Trends in leaf photosynthesis in historical rice varieties developed in the Philippines since 1966,” Journal of Experimental Botany, vol. 58, no. 12, pp. 3429–3438, 2007. View at Publisher · View at Google Scholar · View at Scopus
  37. G. Hirai, T. Okumura, S. Takeuchi, O. Tanaka, H. Chujo, and N. Tanaka, “Studies on the effect of the relative humidity of the atmosphere on the growth and physiology of rice plants: effect of ambient humidity on the translocation of assimilated 13C in leaves,” Japan Journal of Crop Science, vol. 65, no. 3, pp. 460–464, 1996. View at Publisher · View at Google Scholar · View at Scopus
  38. Z. Manzoor, T. H. Awan, M. A. Zahid, and F. A. Faiz, “Response of rice crop (super basmati) to different nitrogen levels,” Journal of Animal and Plant Science, vol. 16, no. 1-2, pp. 52–55, 2006. View at Google Scholar
  39. IRRI, Standards Evaluation System for Rice, 2002,
  40. K. W. Barnes and E. Debrah, “Determination of nutrition labelling education act minerals in foods by inductively coupled plasma-optical emission spectroscopy,” Atomic Spectroscopy, vol. 18, pp. 41–54, 1997. View at Google Scholar
  41. A. Hussain, H. Larsson, R. Kuktaite, and E. Johansson, “Mineral composition of organically grown wheat genotypes: contribution to daily minerals intake,” International Journal of Environmental Research and Public Health, vol. 7, no. 9, pp. 3442–3456, 2010. View at Publisher · View at Google Scholar · View at Scopus
  42. A. Hussain, H. Larsson, R. Kuktaite, and E. Johansson, “Concentration of some heavy metals in organically grown primitive, old and modern wheat genotypes: Implications for human health,” Journal of Environmental Science and Health Part B, vol. 47, no. 8, pp. 751–758, 2012. View at Publisher · View at Google Scholar · View at Scopus
  43. V. L. Singleton, R. Orthofer, and R. M. Lamuela-Raventós, “Analysis of total phenols and other oxidation substrates and antioxidants by means of folin-ciocalteu reagent,” Methods in Enzymology, vol. 299, pp. 152–178, 1999. View at Publisher · View at Google Scholar · View at Scopus
  44. J. Pérez-Jiménez and F. Saura-Calixto, “Literature data may underestimate the actual antioxidant capacity of cereals,” Journal of Agricultural and Food Chemistry, vol. 50, no. 12, pp. 3122–3128, 2005. View at Google Scholar
  45. E. Johansson, H. Nilsson, H. Mazhar, J. Skerritt, F. MacRitchie, and G. Gunnar Svensson, “Seasonal effects on storage proteins and gluten strength in four Swedish wheat cultivars,” Journal of the Science of Food and Agriculture, vol. 82, pp. 1305–1311, 2002. View at Publisher · View at Google Scholar · View at Scopus
  46. R. B. Gupta, K. Khan, and F. MacRitchie, “Biochemical basis of flour properties in bread wheats. I. Effects of variation in the quantity and size distribution of polymeric protein,” Journal of Cereal Science, vol. 18, no. 1, pp. 23–41, 1993. View at Publisher · View at Google Scholar · View at Scopus
  47. MINAGRI (Ministry of Agriculture and Animal Resources), Enabling Self-Sufficiency and Competitiveness of Rwanda rice, 2010,
  48. S. L. Jiang, J. G. Wu, Y. N. B. Thang, Y. Feng, X. E. Yang, and C. H. Shi, “Genotypic variation of mineral elements contents in rice (Oryza sativa L.),” European Food Research and Technology, vol. 228, pp. 115–122, 2008. View at Publisher · View at Google Scholar · View at Scopus
  49. M. A. Shabbir, F. M. Anjum, T. Zahoor, and H. Nawaz, “Mineral and pasting characterization of indica rice varieties with different milling fractions,” International Journal of Agriculture and Biology, vol. 10, pp. 556–560, 2008. View at Google Scholar
  50. P. Ziarati and N. Azizi, “Chemical characteristics and mineral contents in whole rice grains, hulls, brown rice, bran and polished Ali Kazemi rice in Gilan Province–North of Iran,” MIJFAS Journal, vol. 2, no. 24, pp. 1203–1209, 2013. View at Google Scholar
  51. FAO/WHO, Vitamin and Mineral Requirements in Human Nutrition, Food and Agriculture Organization of the United Nations, Rome, Italy, 2nd edition, 2004.
  52. FAO/WHO, Codex Alimentarius Commission. Joint FAO/WHO Food Standards Programme Codex Committee on Contaminants in Foods, 5th Session, Food and Agriculture Organization of the United Nations, Rome, Italy, 2011.
  53. F. Zeng, Y. Mao, W. Cheng, F. Wu, and G. Zhang, “Genotypic and environmental variation in chromium, cadmium and lead concentrations in rice,” Environmental Pollution, vol. 153, no. 2, pp. 309–314, 2008. View at Publisher · View at Google Scholar · View at Scopus
  54. M. A. Rahman, M. M. Rahman, M. Suzie, S. M. Reichman, R. P. Lim, and R. Naidu, “Heavy metals in Australian grown and imported rice and vegetables on sale in Australia: Health hazard,” Ecotoxicology Environ Safety, vol. 100, pp. 53–60, 2014. View at Publisher · View at Google Scholar · View at Scopus
  55. M. Naseri, A. Vazirzadeh, R. Kazemi, and F. Zaheri, “Concentration of some heavy metals in rice types available in Shiraz market and human health risk assessment,” Food Chemistry, vol. 175, pp. 243–248, 2015. View at Publisher · View at Google Scholar · View at Scopus
  56. Y. Shen, L. Jin, P. Xiao, Y. Lu, and J. Bao, “Total phenolics, flavonoids, antioxidant capacity in rice grain and their relations to grain color, size and weight,” Journal of Cereal Science, vol. 49, no. 1, pp. 106–111, 2009. View at Publisher · View at Google Scholar · View at Scopus
  57. H. Y. Chi, C. H. Lee, K. H. Kim, S. L. Kim, and I. M. Chung, “Analysis of phenolic compounds and antioxidant activity with H4IIE cells of three different rice grain varieties,” European Food Research Technology, vol. 225, no. 5, pp. 887–893, 2007. View at Publisher · View at Google Scholar · View at Scopus
  58. C. J. Bergman and F. D. Goffman, “Rice kernel phenolic content and its relationship with antiradical efficiency,” Journal of the Science of Food and Agriculture, vol. 84, no. 10, pp. 1235–1240, 2004. View at Publisher · View at Google Scholar · View at Scopus
  59. C. Rice-Evans, N. J. Miller, and G. Paganga, “Structure antioxidant activity relationships of flavonoids and phenolic acids,” Free Radical Biology and Medicine, vol. 20, no. 3, pp. 933–956, 1996. View at Publisher · View at Google Scholar · View at Scopus
  60. B. Halliwell, “Dietary polyphenols: good, bad, or indifferent for your health?” Cardiovascular Research, vol. 73, no. 2, pp. 341–347, 2007. View at Publisher · View at Google Scholar · View at Scopus
  61. A. Chiang, H. Wu, H. Yeh, C. Chu, H. Lin, and W. Lee, “Antioxidant effects of black rice extract through the induction of superoxide dismutase and catalase activities,” Lipids, vol. 41, pp. 797–803, 2006. View at Publisher · View at Google Scholar · View at Scopus
  62. M. J. Chung, P. A. Walker, and C. Hogstrand, “Dietary phenolic antioxidants, caffeic acid and trolox protect rainbow trout gill cells from nitric oxide-induced apoptosis,” Aquatic Toxicology, vol. 80, no. 4, pp. 321–328, 2006. View at Publisher · View at Google Scholar · View at Scopus
  63. Y. Shao, F. Tang, Y. Huang et al., “Analysis of genotype × environment interactions for polyphenols and antioxidant capacity of rice by association mapping,” Journal of Agricultural and Food Chemistry, vol. 62, no. 23, pp. 5361–5368, 2014. View at Publisher · View at Google Scholar · View at Scopus
  64. A. J. Parr and G. P. Bolwell, “Phenols in the plant and in man. The potential for possible nutritional enhancement of the diet by modifying the phenols content or profile,” Journal of the Science of Food and Agriculture, vol. 80, no. 7, pp. 985–1012, 2000. View at Publisher · View at Google Scholar
  65. A. Van der Borght, G. E. Vandeputte, V. Derycke, K. Brijs, G. Daenen, and J. A. Delcour, “Extractability and chromatographic separation of rice endosperm proteins,” Journal of Cereal Science, vol. 44, no. 1, pp. 68–74, 2006. View at Publisher · View at Google Scholar · View at Scopus
  66. V. Silano, H. C. Bansul, and A. Bozzini, Improvement of Nutritional Quality of Food Crops: A State of the Art report, FAO Plant Production and Protection Paper 34, Rome, Italy, 1981.
  67. FAO, Rice in Human Nutrition, 1994,
  68. Q. G. Yu, J. Ye, S. Yang et al., “Effects of nitrogen application level on rice nutrient uptake and ammonia volatilization,” Rice Science, vol. 20, no. 2, pp. 139–147, 2013. View at Publisher · View at Google Scholar · View at Scopus
  69. L. Kong, Y. Xie, L. Hu, J. Si, and Z. Wang, “Excessive nitrogen application dampens antioxidant capacity and grain filling in wheat as revealed by metabolic and physiological analyses,” Scientific Reports, vol. 7, p. 43363, 2017. View at Publisher · View at Google Scholar · View at Scopus
  70. P. M. Nguyen and E. D. Niemeyer, “Effects of nitrogen fertilization on the phenolic composition and antioxidant properties of basil (Ocimum basilicum L.),” Journal of Agricultural and Food Chemistry, vol. 56, no. 18, pp. 8685–8691, 2008. View at Publisher · View at Google Scholar · View at Scopus
  71. C. S. Wu, Q. H. Gao, R. K. Kjelgren, X. D. Guo, and M. Wang, “Yields, phenolic profiles and antioxidant activities of Ziziphus jujube mill. in response to different fertilization treatments,” Molecules, vol. 18, no. 10, pp. 12029–12040, 2013. View at Publisher · View at Google Scholar · View at Scopus
  72. M. Radi, M. Mahrouz, A. Jaouad, and M. Amiot, “Influence of mineral fertilization (NPK) on the quality of apricot fruit (cv. Canino). The effect of the mode of nitrogen supply,” Agronomie, vol. 23, no. 8, pp. 737–745, 2003. View at Publisher · View at Google Scholar · View at Scopus