Rachelle Ward

SNP in starch biosynthesis genes associated with nutritional and functional properties of rice

Starch is a major component of human diets. The relative contribution of variation in the genes of starch biosynthesis to the nutritional and functional properties of the rice was evaluated in a rice breeding population. Sequencing 18 genes involved in starch synthesis in a population of 233 rice breeding lines discovered 66 functional SNPs in exonic regions. Five genes, AGPS2b, Isoamylase1, SPHOL, SSIIb and SSIVb showed no polymorphism. Association analysis found 31 of the SNP were associated with differences in pasting and cooking quality properties of the rice lines. Two genes appear to be the major loci controlling traits under human selection in rice, GBSSI (waxy gene) and SSIIa. GBSSI influenced amylose content and retrogradation. Other genes contributing to retrogradation were GPT1, SSI, BEI and SSIIIa. SSIIa explained much of the variation in cooking characteristics. Other genes had relatively small effects.

The Diffusion of Moisture in Paddy During Hydration and Dehydration Processes

Hydration and dehydration behavior and the effective diffusivity of paddy during the process of parboiling were studied. Hydration of three different paddy samples (Sherpa low and high head rice yield and Reiziq) were performed below (60°C) and above (90°C) the gelatinization temperature. The hydration period ranged from 5 to 300 minutes at 60°C and 5 to 90 minutes at 90°C. All of the paddy samples showed different hydration behavior below and above the gelatinization temperature, discerned with two different stages at 60°C and three stages at 90°C. Dehydration was carried out at 40°C just after hydration (without tempering the kernel), which mostly took place at the falling rate period. The hydration and dehydration pattern was not different between the high HRY and low HRY paddy, indicating a limited contribution of microfissures to the diffusion rate in the paddy. Five commonly used semi-empirical models were used to predict the hydration and dehydration behavior of paddy and, among them, the Page model was found to be the most suitable. The effective diffusivity during hydration was dependent on the temperature of hydration, which was 1.83 × 10−11 to 2.11 × 10−11 m2/s at 60°C and 6.68 × 10−11 to 7.94 × 10−11 m2/s at 90°C. The effective diffusivity during dehydration depended on the soaking temperature and period of soaking; it was lower for high-temperature-hydrated samples than low-temperature-hydrated samples. The study concluded that the mass water diffusivity was not affected by the microfissures within the paddy kernel, and the hydration pattern was strongly dependent on whether the temperature was above or below the gelatinization temperature.

Wild Oryza grain physico-chemical properties

Of the 22 species within the Oryza genus, only two, O. sativa and O. glaberrima, have been domesticated. Although food security is supported by accessing wild Oryza resources for new genes and alleles which enhance plant performance, wild Oryza grain properties have not been extensively studied. Evaluation of the grain physico-chemical properties of eight wild Oryza species found amylose content, amylopectin structure and cooking properties fell within a narrow range relative to cultivated rice. The amylopectin of the wild species had a lower proportion of short branch chains (DP 6–14) relative to cultivated rice and were all of high apparent amylose content and gelatinization temperature. The grain of the wild species did not elongate to the same extent as the cultivated rice and had lower viscosity parameters. These results highlight how significant physio-chemical changes have been made by human selection in the domestication of rice, especially japonica rice. The wild species may be useful for improving the nutritional value of rice and other cereal crops.