Studies on the agricultural characteristics and suitability for sake brewing of rice varieties bred in Hokkaido, Japan

As of 2012, the rice varieties for sake brewing in Hokkaido are used for approximately 50% of the rice used for sake brewing in the sake breweries in Hokkaido, and these varieties are used even in the sake breweries south of Tohoku prefecture. However, the suitability for sake brewing of rice in Hokkaido has not been evaluated as much as that of ‘Yamadanishiki’, which is known to be highly suitable for sake brewing, and was cultivated in Hyogo prefecture. The cultivation area of rice suitable for sake brewing in Hokkaido is approximately 300 ha, which is less than 0.3% of that of the paddy rice in Hokkaido. It is necessary to raise the evaluation level of the suitability for sake brewing of the rice varieties in Hokkaido and to increase the demand and cultivation area of rice varieties for sake brewing in Hokkaido. In this study, I revealed the positive and negative characteristics of the rice varieties for sake brewing bred in Hokkaido in comparison with those cultivated in Hyogo prefecture, to improve the agricultural characteristics and parameters of sake brewing apitude of rice varieties for sake brewing. In addition, I examined the regional and varietal differences in agricultural characteristics and parameters of sake brewing apitude of rice varieties for sake brewing in Hokkaido. I then analyzed the year-by-year variation of the agricultural characteristics and parameters of sake brewing apitude of the rice varieties for sake brewing, and also the related climatic conditions. Finally, I discussed whether the cultivation and breeding methods used to improve the agricultural characteristics of table rice in Hokkaido can be used to improve the agricultural characteristics and parameters of sake brewing apitude of rice varieties for sake brewing in Hokkaido.1. Comparison of the agricultural characteristics and parameters of sake brewing apitude of rice varieties for sake brewing cultivated in Hokkaido with those of rice varieties cultivated in Hyogo prefecture. The rice varieties for sake brewing, ‘Suisei’, ‘Ginpuu’ and ‘Kitashizuku’, cultivated in Hokkaido had smaller number of grains per head and lighter 1000 grain weight than those cultivated in Hyogo prefecture, ‘Yamadanishiki’, ‘Gohyakumangoku’ and ‘Hyogokitanishiki’, but had higher brown rice yield due to larger panicle number /square m and total spikelet number /square m. In addition, the varieties in Hokkaido showed lower lodging rate due to shorter culm length and superior brown rice quality due to lower white-belly rate and the lower cracked grain rate which elevates the polishing rate necessary to produce high quality sake such as ‘Daiginjo’. On the other hand, the disadvantage of the Hokkaido varieties compared with Hyogo varieties was lighter 1000 grain weight, lower 20-minutes water absorption rate, lower steamed rice water absorption rate, and the higher crude protein content of grains. The higher crude protein content of rice for sake brewing in Hokkaido compared with that in Hyogo prefecture was considered to have been caused by the higher application rate of nitrogen fertilizer. Therefore, in order to improve the suitability for sake brewing of rice in Hokkaido, it is necessary to increase the 1000 grain weight, 20-minutes water absorption rate and steamed rice water absorption rate, and to decrease the crude protein content of grain. 2. Regional and varietal differences in agricultural characteristics and parameters of sake brewing apitude of rice varieties for sake brewing bred in Hokkaido. The brown rice yield was higher in Hokkaido varieties for sake brewing ‘Ginpuu’ and ‘Suisei’ than in table rice varieties ‘Yumepirika’ and ‘Nanatsuboshsi’ cultivated in two regions of Hokkaido, Iwamizawa and Pippu, due to heavier 1000 grain weight, and it was lower in ‘Ginpuu’ than in ‘Suisei’ due to higher sterility rate and lighter 1000 grain weight. The crude protein content of table rice cultivated in Iwamizawa was higher than that cultivated in Pippu, and the protein content of ‘Ginpuu’ was higher that of ‘Suisei’. However, the regional difference (between Iwamizawa and Pippu) was larger than the varietal difference (between ‘Ginpuu’ and ‘Suisei’). Therefore, the selection of cultivation region and varieties are important to reduce the protein content of rice for sake brewing, as in table rice. The 20-minutes water absorption rate was higher in ‘Ginpuu’ than in ‘Suisei’ due to higher occurrence rate of white core rice. The steamed water absorption rate of rice did not significantly vary with the cultivation region or variety. The lodging resistance, brown rice yield and brown rice quality of the two Hokkaido rice varieties for sake brewing were superior to those of either of ‘Yamanishiki’ from Hyogo prefecture. However, the 1000 grain weight, crude protein content, 20-minutes water absorption rate and steamed water absorption rate of the two rice varieties for sake brewing in Hokkaido were inferior to those of ‘Yamadanishiki’. Therefore, it is considered necessary to improve the 1000 grain weight and crude protein content by the same method as that for table rice varieties, and to improve the 20-minutes water absorption rate and steamed water absorption rate by using the data used for nationwide analysis of suitability for sake brewing of rice. 3. Influence of the climatic conditions on the agricultural characteristics and parameters of sake brewing apitude of rice varieties for sake brewing bred in Hokkaido. I analyzed the year-by-year variation of the agricultural characteristics of two rice varieties for sake brewing ‘Ginpuu’ and ‘Suisei’ and two table rice varieties ‘Yumepirika’ and ‘Nanatsuboshsi’ cultivated at Iwamizawa and Pippu in Hokkaido. I also analyzed the climatic conditions related to these characteristics, which are the daily highest temperature, lowest temperature, average temperature, and the solar radiation estimated from sunshine hours. The study period was a total of 80 days, consisting of eight successive 10-day periods before and after heading. The percentage sterility greatly varied with the year in all of the four varieties, and the variation was largest in ‘Ginpuu’ and smallest in ‘Suisei’. In 2009, the year of this study, cold damage was severe, and the percentage sterility was signnicantly different from that in other years. There was a negative signrncant correlation between the daily highest temperature from 20 to 11 days before heading (-II period) and the percentage sterility. Because the -II period is the boot stage, the daily highest temperature at this stage was considered to influence the percentage sterility, and I consider this one of the reasons why the percentage sterility greatly varied with the year. The difference in the percentage sterility between 2009 and other years was largest in ‘Ginpuu’ and the smallest in ‘Suisei’. Cold tolerance at the boot stage was also lowest in ‘Ginpuu’ and largest in ‘Suisei’. Therefore, I consider that the varietal difference in cold tolerance brought about the difference in percentage sterility between 2009 and other years, and that this is the main reason for the varietal difference in the year- by-year difference of the percentage sterility. The year-by-year variation of the agricultural characteristics was smallest in 1000 grain weight. There was a positive signnicant correlation between the daily highest temperature during the -II period and the 1000 grain weight in all four varieties, and between the daily highest temperature from 11 to 20 days after heading (+II period) and 1000 grain weight, in the two rice varieties for sake brewing. The 1000 grain weight in 2009 was not greatly different from that in the other years, and I considered that this was one of the reasons why the year-by-year variation of the agricultural characteristic was smallest in 1000 grain weight. The year-by-year variation of the suitability for sake brewing was largest in white core rate followed by crude protein content. The variations in 20-minutes water absorption rate and steamed rice water absorption rate were relatively small. There was a negative significant correlation between the daily highest temperature in the – II period and the crude protein content in ‘Ginpuu’, and between the daily highest temperature in the + II period and 20-minutes water absorption rate in ‘Ginpuu’ and ‘Suisei’. Furthermore, there was a signrncant negative correlation between the daily highest temperature from 21 to 30 days after heading (+III period) and the steamed rice water absorption rate in ‘Suisei’. There was a significant positive correlation between the daily highest temperature in the - II period and white core rate in ‘Suisei’. From these results, in the year with high daily highest temperature during the -II, the 1000 grain weight was considered to increase in ‘Ginpuu’ and ‘Suisei’ and the crude protein content to decrease in ‘Ginpuu’. In the year with high daily highest temperature during the +II period, the 1000 grain weight was considered to increase and 20-minutes water absorption rate to decrease in ‘Ginpuu’ and ‘Suisei’. In the year with high daily highest temperature during the +III period, steamed water absorption rate was considered to decrease in ‘Suisei’. Information on the relationship between the daily highest temperature and the parameters of sake brewing apitude would be useful for sake breweries in districts other than Hokkaido, if they use the rice bred in Hokkaido. Furthermore, the deep water irrigation technology recommended for reducing the sterility of table rice was considered to increase the 1000 grain weight of ‘Ginpuu’ and ‘Suisei’, to reduce the crude protein content of ‘Ginpuu’ and to increase the white core rate in ‘Suisei’. The findings on the agricultural characteristics and parameters of sake brewing apitude of rice varieties for sake brewing bred in Hokkaido obtained in this study will contribute to the improvement of cultivation technology and stable production of high-quality rice for sake brewing in Hokkaido, and will be useful for breeding of the rice suitable for sake brewing in the future.