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Cereal Chem. 89(3):168-175Elevated nighttime air temperatures (NTATs) occurring during critical grain-filling stages affected rice physicochemical properties, which impacted functional quality. Six cultivars were grown at multiple field locations from northern to southern Arkansas during 2007 to 2010. Nighttime temperatures were recorded throughout production at each of the locations, and 95th percentiles of NTATs were calculated for each cultivar's reproductive (R) stages. Amylose content and crude protein content decreased linearly, whereas total lipid content increased linearly, with increasing NTATs occurring during the grain-filling stages (R6-R8). Effects of NTAT on proximate composition influenced functional properties. Peak viscosities increased linearly as NTAT increased, whereas setback viscosities decreased. Setback viscosities were linearly correlated to NTATs for medium-grain cultivars, but correlations were quadratic for the long-grain cultivars. Gelatinization temperatures increased linearly with increasing NTAT. The R stages in which correlations were strongest varied by cultivar and by property, hypothesized to result from differences in kernel development patterns among cultivars. These findings have significant implications for rice production scientists and processors, in that understanding the effects of NTAT on physicochemical and functional properties may help explain and reduce quality variation.Recent studies in both controlled-temperature and field-scale environments have established that elevated nighttime air temperatures (NTATs) occurring during critical grain-filling stages affect rice kernel development, resulting in reduced yield, increased kernel chalkiness, and reduced milling quality (Peng et al 2004; Cooper et al 2006, 2008; Ambardekar et al 2011; Lanning et al 2011). Other studies have shown that the chemical makeup of starch is affected by elevated NTAT, as evidenced by decreased amylose content (AC) and changes in ratios of long-to shortchain amylopectin (Counce et al 2005; Cooper et al 2008). Several hypotheses have been presented to explain the effects of NTAT stress, including reduced substrate supply to the endosperm, initiating slow starch granule growth and irregular granular organization (Fitzgerald and Resurreccion 2009) and disruption of enzymatic activity responsible for starch formation (Counce et al 2005).Although the underlying mechanisms that tie the effects of NTAT to the structural and functional changes of starch are not clearly established, these findings are critical to rice end-use applications, because functional properties of milled rice, which directly impact cooking and sensory quality, are primarily determined by starch physicochemical properties.AC of a given rice strain is determined by the expression of two alleles of a polymorphic waxy gene, Wx a and Wx b , which regulate amylose synthesis by controlling the activities of grain-bound starch synthase (GBSS) enzymes (Counce et al 2005). Suzuki et al (2003) reported that mutations to Wx a and Wx b a...

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