Abstract
We evaluated a method for testing the spiral growth of seminal roots in order to increase the seedling establishment rate of direct-seeded rice on the soil surface in flooded paddy fields. For the morphological observation of seminal roots, we used 1/2 MS medium supplemented with 10g/l sucrose and 2g/l gellan gum, and placed sterilized dehulled rice seeds on the medium. When ion exchange water was poured onto the medium (3cm depth), varietal differences in the frequency of the spiral root type were observed. Since seminal roots penetrated easily into the gellan gum medium at a low concentration, we used 0.25g/l gellan gum medlum and attempted to parametrize the spiral growth of seminal roots (Fig.1). Value of α/β was assumed to represent the degree of spiral growth of seminal roots. The α/β value (average within lcm of seminal root length) was closely related to the seedling establishment rate in paddy fields (r=0.967, P<0.OO1). Thereafter, to determine the measuring points, we projected the α/β value on a fixed point with linear interpolation and extrapolation. The α/β value for 9mm of semlnal root length on a fixed point showed the highest positive correlation with the seedling establishment rate (r=0.941, P<0.O1). Consequently, it was considered that the use of gellan gum medium at a low concentration was effective for the development of on in vitro testing method to increase the establishment rate of direct-seeded rice on the soil surface in flooded paddy fields.
