**6. Conclusion**

Genetics has advanced people's understanding of rice grain quality. The identification of the genes controlling the different quality traits has certainly helped breeders in improving rice varieties, especially with the capacity to deliver those outcomes using genome-wide genotyping tools. In the case of AC, GT, and GC, knowledge of the genetic factors has already translated into molecular markers; these tools are being applied in breeding programs with a caveat: the genetics of the extreme classes of GT and GC are now understood; for programs aimed at targeting for the intermediate phenotype, the gene(s) have yet to be identified. For AC, the SNPs coding for all classes are likely to be known; but there are other factors that contribute to pasting properties. The genetics behind these other factors have yet to be fully understood.

Waxy rice varieties do not have amylose and thus could not be grouped into quality classes based on this property. Within the waxy class, rice varieties are very diverse and new approaches in characterising and classifying them are being developed. The RVA is a promising tool for screening eating and cooking properties of waxy rice and in defining the quality classes. However, since the viscosity curves within each amylose class are different, it is important to understand how the other factors affecting pasting properties interact with AC.

The challenge now is to find new genes for rice quality beyond AC, GC, and GT. Development of high-throughput genotyping technologies is progressing at a hectic pace. The progress, then, of finding novel sensory quality genes hinges on the pace of development of phenotyping tools that target traits that rice consumers find difficult to characterise.

#### **7. Acknowledgment**

300 Genetic Diversity in Plants

Though useful in predicting quality, AC, GT, and GC do not paint the whole picture of rice quality. Varieties identical in these three traits may be grouped into one quality class based on these parameters but consumers easily distinguish a premium variety from a lower quality one (Champagne et al., 2010). This could lead to low rates of adoption of newly developed improved varieties by farmers. Unfortunately, consumers are rarely able to describe the difference when they eat supposedly identical rice varieties (based on AC, GT, and GC if applicable). Hence, the next steps in discovering genes for sensory quality include finding descriptors for the sensory experience and developing phenotyping tools that can be used to quantify these descriptors. Once the phenotype is known, association mapping can begin, using appropriate populations. Such an approach will then lead to the delivery of

An example of the value and need for phenotyping tools is the trait of aroma. Aroma is easy to define as present or absent in cooked rice. It was therefore possible to develop a phenotyping tool, in this case gas chromatography (Bergman et al., 2000), and then use mapping populations, genome-wide genotyping and sequencing of candidate loci to find genes and allelic variation (Kovach et al., 2009). Unfortunately, other sensory properties of rice are more abstruse because they are not as easily described by consumers. To find adjectives for these other sensory properties, descriptive sensory profiling is employed; a trained sensory panel assesses food for aroma, texture, and flavour (Champagne et al., 2010). Comparisons by a trained panel between similar varieties (in terms of AC, GT) but classed as premium and second-best showed that slickness, roughness, and springiness were textural attributes that separated the two classes while sweet taste, popcorn flavour, and metallic mouthfeel were the flavour attributes (Champagne et al., 2010). Without phenotyping tools, these traits could not be associated with genetic loci. Thus, discovering

novel sensory quality genes goes in tandem with developing phenotyping tools.

Genetics has advanced people's understanding of rice grain quality. The identification of the genes controlling the different quality traits has certainly helped breeders in improving rice varieties, especially with the capacity to deliver those outcomes using genome-wide genotyping tools. In the case of AC, GT, and GC, knowledge of the genetic factors has already translated into molecular markers; these tools are being applied in breeding programs with a caveat: the genetics of the extreme classes of GT and GC are now understood; for programs aimed at targeting for the intermediate phenotype, the gene(s) have yet to be identified. For AC, the SNPs coding for all classes are likely to be known; but there are other factors that contribute to pasting properties. The genetics behind these other

Waxy rice varieties do not have amylose and thus could not be grouped into quality classes based on this property. Within the waxy class, rice varieties are very diverse and new approaches in characterising and classifying them are being developed. The RVA is a promising tool for screening eating and cooking properties of waxy rice and in defining the quality classes. However, since the viscosity curves within each amylose class are different, it is important to understand how the other factors affecting pasting properties

**5. Future directions** 

**6. Conclusion** 

interact with AC.

factors have yet to be fully understood.

validated genotyping tools to breeding programs.

The authors thank the people who provided rice materials mentioned in Section 2 of this chapter: Dr Kent McKenzie (California Cooperative Research Centre) for the very-low amylose mutants, Dr Wu Dianxin (Zhezhiang University) for RS111, Dr Park (Korean Rural Development Administration) for Ilpumbyeo and Goami 2, and the Genetic Resources Centre (IRRI) for the set of diverse waxy varieties.

The authors also thank the quality evaluation team of the GQNC for providing rice quality phenotyping data of diverse rice samples.

The authors appreciate the financial assistance extended by the Rural Industries Research and Development Corporation.

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