Effects of Growing Temperature and Nitrogen Supply on Grain Chalkiness in Rice

Grain chalkiness or white patches in rice kernel is a major problem in almost all types of rice, as it lowers the mill-out yield and consumer acceptance. Adverse environmental conditions, particularly higher temperatures during grain filling have been reported to enhance chalkiness. In this study, the effects of two different nitrogen (N) levels and temperature regimes, on the extent of chalk (%) were tested. Interestingly, chalkiness was higher in the high N grown plants, which was further exacerbated by higher temperatures. Thus, in plants grown with higher N with more seed set, the supply and/or synthesis of carbohydrates is the limiting factor that is further impaired at higher temperatures and results in increased proportion of chalky grains. Results from the SEM analysis of starch packaging in endosperm of these grain samples, in relation to chalkiness, are discussed.