Cereal Chem. 82(6):645-648Important rice grain quality characteristics such as percentage of chalky rice kernels are affected by both high and low night temperatures and by different day and day/night temperature combinations. High nighttime temperatures have also been suspected of reducing rice milling quality including head rice yields. Experiments to confirm or refute this have not been reported. A controlled climate experiment was conducted. Conditions in the chambers were identical except between 2400 and 0500 hours (midnight and 5 am). For those times, two temperature treatments were imposed: 1) 18°C (low temperature treatment) and 2) 24°C (high temperature treatment). Two cultivars were tested: LaGrue and Cypress. The high temperature treatment reduced head rice yields compared with the low temperature treatment. Grain widths were reduced for the high temperature treatment compared with the low temperature treatment. There was no effect of temperature on grain length or thickness. Amylopectin chain lengths 13-24 were increased by the high temperature treatment by ≈1%. Future research will focus on determining whether genetic variability exists among cultivars in their head rice yield response to high temperatures. After identifying a source of resistance to high temperature effects, this characteristic can be incorporated into rice cultivars. In addition, ways to reduce this effect, including biotechnological remedies, have the potential for increasing rice yield and quality.

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Cereal Chem. 83(3):275-283Long-grain rice cultivars Francis and Wells and hybrid XL8 Clearfield were harvested from two locations at three harvest moisture contents (HMC) in 2003. The rough rice was dried, fractionated into thin, medium, and thick fractions, and milled. Physicochemical properties of unfractionated and fractionated samples were determined. The effects of HMC and location on thickness distributions were investigated and the weightedaverage physicochemical properties of the thickness fractions were compared with those of unfractionated rice. Generally, the growing location and HMC affected kernel thickness distributions, green kernel content, fissured kernel content, and head rice yield (HRY). As kernel thickness within samples increased, amylose content increased and the protein content and α-amylase activity decreased. Thick fractions had greater peak viscosities than medium and thin fractions. The thin, medium, and thick fraction physicochemical property weighted averages provided good predictions of most unfractionated rice sample properties. However, this approach was not entirely accurate for predicting HRY, milled rice total lipid content, and bulk density.

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