1980), the BBCH system (Lancashire et al., 1991), andHaun (1973). Zadoks et al. (1974) is an adaptation of The large area of rice (Oryza sativa L.) production worldwide is Feekes' (1941) scale (with 23 subdivisions) but further critical to the well being of large numbers of the world's people. Yet delineated. The IRRI (1980) scale is a 10-point system for rice, the most important single plant species for human nutrition, there is not a widely used growth staging system. Despite good points Paul A. Counce, University of Arkansas, Rice Research and Extensionrather than an arbitrary number (e.g., 10, 11, 99, or Center,

Cereal Chem. 85(3):276-282Rice quality can vary inexplicably from one lot to another and from year to year. One cause could be the variable temperatures experienced during the nighttime hours of rice kernel development. During the fall of 2004, a controlled temperature study was conducted using large growth chambers, testing nighttime temperatures of 18, 22, 26, and 30°C from 12 a.m. until 5 a.m. throughout kernel development, using rice cultivars Cypress, LaGrue, XP710, XL8, M204, and Bengal. As nighttime temperature increased, head rice yields (HRY) significantly decreased for all cultivars except Cypress and Bengal, for which HRY did not vary among nighttime temperature treatments. Kernel mass did not vary among temperature treatments for any cultivar. Grain dimensions generally decreased as nighttime temperature increased. The number of chalky kernels increased with an increase in nighttime temperature for all cultivars but Cypress. The amylose content of Cypress and LaGrue was significantly lower at the nighttime temperature of 30°C, while total brown rice lipid and protein contents did not vary among temperature treatments for all cultivars.Rice is primarily consumed as an intact kernel and therefore production quality is largely measured by head rice yields (HRY), which is the mass percentage of rough rice kernels that remain as head rice (kernels that are ≥75% of a whole, milled kernel (USDA 2005). Broken rice is worth only 50-60% of the value of head rice, meaning that a reduction in HRY can have severe economic repercussions for rice producers. Therefore, maximizing HRY is a major concern. Producers can influence HRY by optimally choosing harvest dates to avoid kernel fissure formation due to rapid moisture adsorption in the field (Kunze 1977). Improper drying and storage procedures can also cause kernel fissuring that can reduce HRY (Daniels et al 1998).While HRY is determined in part by production practices, HRY can vary inexplicably from year to year and often from field to field, making it difficult for producers to predict yearly income and for processors to maintain a consistent end product. Moreover, in a given year, HRY can be uniform in one cultivar of rice and yet variable in another cultivar, leading to the suspicion that some cultivars are more resistant to quality variation. To achieve uniformity in the quality characteristics of rice, it is first necessary to have a clear understanding of the causes of these quality variations.Rice quality can be influenced by genetics and environmental conditions such as ambient temperature during rice plant development (Webb et al 1979). While rice genetics can be altered through breeding programs, environmental temperatures are difficult to predict and can only be manipulated to some extent with the choice of planting dates. Environmental temperature during kernel development may play an integral role in causing the observed, unexplained fluctuations in rice grain quality (Cooper et al 2006).Historical analyses have indicated that decreased yields were ...

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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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