6. Amylose contne of rice varieties in northern Japan

Kazuyoshi Takeda-Institute for Agricultural and Biological Sciences Okayama University, Kurashiki, 710 AND Tadao Sasaki-Hokkaido Central Agricultural Experiment Station, Iwamizawa, 069-03, Japan.


Rice starch consists of amylose and amylopectin, and the stickiness of cooked rice largely depends on the amylose content. In Japan, rice with relatively low amylose (below 18%) is preferred. However, rice produced in Hokkaido generally contains more amylose than those produced in southern Japan. Recently, it was learned that the amylose content of rice endosperm was influenced by the temperature during the ripening period (Okuno 1985). To determine the extent of changes in amylose content, 11 rice varieties grown in Hokkaido were grown at Iwamizawa (central Hokkaido, ca. 20-30 degrees in the ripening period) and at Kurashiki (southwestern Honsu, ca. 25-35 degrees) in the 1985 season. The same varieties were also grown in phototrons in which two temperature ranges, 13-23 degrees and 23-33 degrees were maintained throughout the ripening period.

The varieties headed at Iwamizawa in early August, and Kurashiki in late July. The mean amylose contents for all varieties were 20.3% at Iwamizawa, 17.0% at Kurashiki, 21.9% in the phytotron maintained at 13-25 degrees and 18.7% at 23- 33 degrees, and showed a strong correlation (r=0.95, P<0.05) with temperature. It was estimated that a one-degree rise of temperature in ripening period would result in a decrease of 0.365% in amylose content. Varietal means ranged from 18.3% in the variety Shimahikari (a high quality variety produced at Hokkaido) to 21.1% in the variety Tomoyutaka. An analysis of variance of the data showed that both the variety and the environment had a highly significant effect on amylose content, when tested against the interaction (Table 1 Analysis of variance for amylose content). In terms of components of variance, the temperature effect was about 5 times as large as the varietal effect which was 0.909% in standard deviation. The variety-temperature interaction was small within the range of varieites and temperature conditions used in the experiment.


Table 1. Analysis of variance for amylose content




Reference

Okuno, K., 1985. Environmental control of gene expression in mutants of rice. RGN 2: 65-66.