Factors Determining Genotypic Variation in the Speed of Rice Germination

Rapid germination is important for both direct seeded rice in the field and for the production of germinated brown rice for healthy food. This study aims to evaluate genotypic differences in germination speed and identify characteristics that determine germination speed. Seven experiments were conducted to determine (i) the impact of dehulling on water absorption and germination, (ii) variety consistency in germination speed across crops grown in three years, and (iii) the effect of grain size. Germination speed in both paddy rice and dehulled brown rice was significantly correlated with grain moisture content at early stages of soaking, however significant interaction of genotype and grain type (paddy and brown rice) existed and varieties differed in their response to dehulling. Germination speed of grain from crops exposed to water deficit in the field was slightly slower than those with higher water supply. Sherpa/IRAT109 genotypes with smaller grain size tended to germinate faster than larger grain, however no significant effect of grain size existed among diversity set varieties. It was concluded that genotype ranking in germination speed was consistent across years and water availability conditions, and that barriers to water absorption in hull and pericarp were important determinants of germination speed. The existence of genotypic variation in germination speed has management implications for both field crop establishment and paddy germination in food processing

Effect of Early Harvest and Variety Difference on Grain Yield and Pasting Properties of Brown Rice

Green grains that are harvested before maturity and dehulled have been reported to have higher nutritional value than fully matured brown rice. Two years of aerobic field experiments were conducted to determine the effect of variety, early harvest and their interaction, on grain yield and pasting properties of brown rice. Eight varieties were grown under well-watered or water deficit conditions and harvested between 15–35 days after flowering (DAF). The maximum yield of green rice was obtained when crops were harvested between 20–25 DAF for well-watered condition and 15–20 DAF for water deficit condition. The paddy yield on these early harvest dates was on average 66% of mature paddy rice yield. Varieties were consistent in paddy yield at early harvest 20–25 DAF with correlation coefficient being 0.897 ** between the two years. Rapid visco-analysis (RVA) showed that developing grains had lower pasting viscosities than mature grains. However, the variety difference had a greater effect on pasting viscosities than the harvest time. Varieties were consistent in pasting characteristics between early and mature harvests, and between growing seasons. Water deficit reduced grain yield but did not significantly affect the pasting characteristics of flour gel, amylose and protein content. The RVA showed that final viscosity and setback viscosity in brown rice flour harvested at 15 DAF were only 84% and 76% of those in mature brown rice, indicating that developing grains were likely to produce softer cooked rice than mature grain. The results on differences in pasting characteristics between developing and mature grains provide more options in developing food products with desired gel properties

Fissured grain and head rice yield of crops harvested manually or by combine at different ripening stages in Cambodia

Combine has been well adopted by smallholders in lowlands of Cambodia and is contributing to the development of mechanized rice production for commercial purposes. Broken rice is a major issue for the commercial rice product, and fissured grain at harvest leads to broken rice and lowers head rice yield (HRY) during milling. Factors that determine grain fissures and broken rice were obtained from three studies: an on-farm study of fissured grain, a research station experiment of fissured grain and broken rice harvested at different ripening stages and a mill study of fissured and broken rice during drying and milling processes in Cambodia. There was significant variation in fissured rice percentage among 20 farms sampled, and the fissured grain was negatively correlated with grain moisture content at harvest. Time of harvesting was crucial, as delay in harvesting after 25\ua0days after flowering (DAF) often resulted in lower grain moisture content and higher fissured grain, which subsequently reduced HRY. However, the optimum time of harvesting varied across four seasons for crops harvested manually or by combine. In some years, crops harvested at 35 DAF had rather low per cent fissured grain with subsequently high HRY, this may have been associated with slightly lower temperatures. The mill study showed that fissured grain developed during the drying, storage and milling processes. It is concluded that while grain moisture content at the time of harvest may be used as an indication of subsequent HRY, the latter was more strongly related to fissured grain at harvest