Grain quality and nutrition of japonica rice

Background

At present, amylose estimation and gel consistency and gelatinization temperature are considered routine screening parameters in breeding programs to capture cooking quality. To be able to make a distinction in textural and cooking quality properties between several high-quality Japonica varieties, other parameters, such as starch quality, instrumental texture, and viscoelastic properties, must be linked with the routine parameters through a holistic modeling and underpin the influence of these parameters on textural characteristics and acceptability of each predicted cooking and eating quality groups or ideotypes. Establishing this cooking and eating quality (CEQ) properties together with milling, chalk and appearance qualities for several benchmarks of Japonica high-quality lines and establishing screening protocols are important for TRRC.  Similarly, while many breeding programs have selected low amylose in Japonica and intermediate amylose in Indica species, the low amylose content is linked to a very high glycemic index (GI). Hence, there is a need to make systematic efforts to screen the Japonica germplasm, which could possess low GI properties with acceptable texture and position these donors for future low GI breeding programs.

Accomplishments

Output 1: Establishment of ISO17025 grain quality protocols with good heritability

• Successfully added grain quality evaluation services to the GQNSL's scope of ISO/IEC 17025 accredited test parameters after the Philippine Accreditation Bureau granted the IRRI-Grain Quality and Nutrition Services Laboratory (GQNSL) ISO/IEC 17025 accreditation in 2010 for testing rice grains, plants, and soil. Routine rice quality testing for physical and milling qualities as well as cooking and eating quality traits is one of these services. To determine heritability, these standard quality checks were applied to Japonica rice types provided by TRRC.

Output 2: Understanding the phenotypic variation and genetic diversity of Japonica for grain quality attributes

• Profiled for a group of 423 Japonica rice varieties for the physical, milling and CEQ quality traits. The subpopulations of this Japonica line are admixed Japonica (79), temperate Japonica (130), and tropical Japonica (214). 

• Identified cooked and raw grain length, width, and shape-associated genetic variants through Single nucleotide polymorphisms (SNP-based) genome-wide association study. Significant associations with raw grain width were observed on chromosomes 3 and 11, while for cooked grain width only chromosome 5 peak was identified.

• Detected a significant SNP (CT; effect = 0.58, log10(p) = 9.83) in the intronic region of the gene E3 ubiquitin ligase (LOC Os10g35920), a novel area for cooked grain shape, such as GSc10.1, from chromosome 10 utilizing the single locus genome-wide association research approach. 

Output 3: Models developed to identify premium quality based on cooking and eating quality and linking with texture

• Developed comprehensive cooking and eating quality models to classify rice varieties of all subspecies into seven different cooking and eating quality classes. Results applied to Japonica germplasm showed that distinct CEQ classes were predicted with 75.43% accuracy.  In this particular set of Japonica varieties, 60 lines that would match the textural quality of Koshihikari (class E) and 40 lines that matched the quality class of Waxy Rice (class D) were identified. These two classes are distinct from other types as it has low amylose content and is sticky in texture when cooked. 

Output 4: Establishing the method for estimating the glycemic index values of rice in Japonica germplasm

• Investigated the use of amylolysis, starch indices, and starch fractions as factors for GI prediction in order to build an in vitro approach for GI screening in rice. This study showed that in vivo GI is significant to very strongly connected with resistant starch (RS), amylose (AM1, DP>1000, and AM2, 121DP1000), and short-chain amylopectin (SCAP, particularly SCAP of DP 25-36). While whole grains, a modified in vitro amylolysis procedure, a reduced sample need, and lower enzyme activity were used to evaluate starch hydrolysis and glucose area under curve, greater correlations were seen even after 180 minutes.