Nursery method for mechanical transplanting of giant-embryo rice cultivar 'Haiminori' [Japanese]

摘要

Factors adversely affecting seedling emergence and establishment of giant-embryo cultivar 'Haiminori' were studied and a nursery method for mechanical transplanting was developed. In 'Haiminori', the germination rate was 96.7%, but a low seedling emergence rate (69.2%) and low establishment rate (33.0%) were sometimes recorded. This suggested that 'Haiminori' was inferior in seedling growth after germination. The low seedling emergence rate and establishment rate were attributed to a high malformation rate (50.2%) and large amount of sugar exudation from the seeds during germination. However, threshing damage to the large embryos affected neither the seedling emergence rate nor establishment rate. Neither seedling emergence rate nor establishment rate of 'Haiminori' were improved by changing imbibition and greening temperature, harvest time, nursery media, and sowing rate. Seedling height in chaff mats was higher than in soil. In the chaff mats, the tensile strength of the seedling mats was 0.46 N, twice as strong as 0.23 N in soil. A sufficient number of seedlings was obtained at a sowing rate of 270 g per nursery box. In conclusion, 'Haiminori' was inferior in seedling growth after germination, which was mainly attributed to a high malformation rate and large amount of sugar exudation from the seeds. Seedling mats suitable for mechanical transplanting were obtained with the chaff mats and at a sowing rate of 270 g per nursery box.