The Relationship between Germination Rate of Rice Seeds at Low Temperature and the Subsequent Early Growth of Seedlings : V. Germination and emergence of radicle at low temperature

The present studies were conducted to clarify the varietal differences of the radicle emergence under low temperature condition (15°C). The author used 46 new and old varieties which have been bred in Hokkaido and posses different degrees of germinability at low temperature. There were no seeds in which the radicle emergence of seminal roots preceded germination. The days from germination to the radicle emergence varied 2-4 days among all varieties and about 90% of the seeds commenced the radicle emergence at 6-8 days after germination. The plotted curves of the radicle emergence which began at 6-9 days and ended 12-14 days from seeding, closely resemble the plotted sigmoid curves in the germination at 15°C, although the initiation was delayed by 2-4days. Both the rooting coefficients and the number of days from germination to the radicle emergence indicated significant differences among varieties and the correlation coef ficients between both characters was highly significant showing r=-0.387. In contrast with this, a non-significant relation was recognized between the germination coeffients and the number of days from germination to the radicle emergence (r=-0.039). A partial correlation between the above characters was calculated by excluding thc effect of the germination coefficients and a highly significant value at a 0.1% level (r'=-0.919) was seen. It is assumed that the germination at low temperature are not always accompanied by the initiation of radicle emergence of seminal root which is controlled in such a way as to occur after the germination. Therefore it is possible that both characters are governed by different factors to some extent. Since a highly significant correlation existed between the germination and rooting coefficients (r=0.924), it seems to be of considerable importance that the varietal improvement promoting the germinability at low temperature may be effective for the selection of the high rooting ability which may lead to the breeding of a variety suitable for direct sowing floodcd paddy field in the cooler region.