Abstract:

The temperature of rice grain-filling stage is the primary ecologic factor for rice qualities. Yangdao6 (indica rice) and Wuyujing3 (japonica rice) were used to study the effects of higher temperatures in different filling stage on rice qualities and characteristic values of Rapidvisco-analyzer with climatic cabinets. The temperature treatments were as follows: higher temperature (30℃) in whole grain-filling stage (A); higher temperature in early grain-filling stage (GFS) and optimum temperature (23℃) in later GFS stage (B); optimum temperature in early GFS and higher temperature in later GFS(C); optimum temperature in whole GFS (D,CK) (Table 1). The results showed that, different cultivars had different responses to various temperature treatments, and so did the various indexes of rice qualities. With high temperature in GFS, rice grain chalkness rate and grain chalkness were increased, while the brow rice rate, the milled rice rate and the head rice rate decreased significantly (Table 2); the effects of GFS temperature on rice AC value were various with cultivars, under high temperature treatments, Yangdao 6’s AC value were increased, while Wuyujing3’s AC value decreased (Fig.1). Under high temperature treatments, both cultivars performed higher protein content (Fig.2), higher Gelatinization temperature, Final viscosity, Consistency and Setback, lower Peak viscosity, Hot viscosity, and Breakdown (Table 3). Compared with D treatment, the rice qualities were affected by a treatment mostly, moderately by B treatment, while least by C treatment. The rice quality indexes under A and B treatments were various greatly with those under C and D treatment; while those under A treatment were various slightly with those under B treatment, and so did those under C treatment with D treatment. It can be concluded that: the period from heading to the 20 days later is the vital stage for whole rice quality in response to higher temperature, which affects rice qualities decisively; while the effect of the temperature in the later stage (beyond 20 days from heading) is slight. And the effect of higher temperature on some parameters of quality differs with cultivar, even though higher temperature degrades whole rice quality in general.

Key words: Rice(Oryza sativa), Rice quality, Higher temperature, Rapidvisco-analyzer