Abstract
Giant-embryo rice cultivar ‘Koshiguruma’ which has been recently developed and released in the Niigata Prefecture, has the merit of producing a large amount of GABA, but has a defect of lower rate and non-uniformity of seedling emergence. The lower rate of seedling emergence and poor establishment of root mat in a seedling box did not ensure the better stand of seedlings, when they were transplanted to a paddy field with a transplanting machine. We examined the methods for increasing the rate of seedling emergence and the tensile strength of seedling mat of ‘Koshiguruma’. The seeds of ‘Koshiguruma’ germinated at a slower rate than those of ‘Koshihikari’ used as a control cultivar, but the final germination percentage was 98% equivalent to that of ‘Koshihikari’. However, the rate of seedling emergence of ‘Koshiguruma’ was 67% in the seedbed-soil, which was significantly lower than 98% in ‘Koshihikari’. Disinfectant application to the soil or heat-budding method did not recover the seedling emergence. On the other hand, the pool raising method of seedlings increased the plant height, root length and tensile strength of seedling mat in ‘Koshiguruma’. Seeds of 300g per nursery box were needed for establishment of seedling emergence of ‘Koshiguruma’ in soil and for sufficient tensile strength of the seedling mat, which was twice the standard sowing rate. Even by this improved method the vacant hills after machine transplanting was 9.3%, which was 4 times higher than that of ‘Koshihikari’. Such a high rate of vacant hills may be due to the floating on water surface of non-germinating seeds coexisting with germinated seeds. Further investigation on raising method will be needed to reduce vacant hills for establishment of ‘Koshiguruma’ by machine transplanting.
