Breeding of a new giant embryo rice cultivar "Koiazusa" with high tolerance to cool temperature

"Koiazusa" is a new rice cultivar with a giant, nonglutinous embryo developed at the National Agricultural Research Center for Tohoku Region, NARO, registered as Paddy Rice "Norin 407" by the Ministry of Agriculture, Forestry and Fisheries (MAFF) in 2005. It was selected from the progenies of a cross Hokkai269/Ouu316 carried out in 1989. The maturity is almost same as "Akitakomachi" and is classified as early group in Tohoku region. Compared to "Akitakomachi," the culm height is shorter, and lodging resistance is stronger. The grain shape of the brown rice is a slightly more round, and the 1000 grain weight is slightly less. In terms of embryo size, the length is about 1.3 times longer and the weight is about 1.9 times more than that of "Akitakomachi." The grain yield is almost same as that of "Akitakomachi." It has true resistance genes to blast, "Pia, Pik", while the field resistance to leaf and panicle blasts are weak. Cool weather tolerance at its reproductive stage is very high and seed dormancy is easy to overcome. Grain quality is poor because luster is inferior. As for the eating quality, the milled rice is clearly inferior to "Akitakomachi," but the pre-germinated brown rice is only slightly inferior to "Akitakomachi." The Gamma-aminobutyric acid (GABA) content in the grain is high and that of the pre-germinated brown rice is about 1.6-1.8 times as high as that of the usual varieties. It can be expected as an emergent high-GABA brown rice for processing. "Koiazusa" can be adapted to Tohoku district and other areas where "Akitakomachi" can be grown. Its cultivation requires sowing about 1.5 times the normal amount of seeds, since the emergence of its seedlings is inferior to that of common varieties.