抄録
This experiment was made on the strength requisite for detaching rice grain from its pedicel or rachilla using unbonded gauge type transducer (UT 1kg) and automatic null balancing recorder. Materials were 48 cultural varieties of paddy rice taking any three ears of each at about 50 days after heading. Results were as follows. 1. The ratio of the breaking tensile strength, i. e. force strains along the direction of pedicel, to the breaking bending strength, i. e. force strains perpendicular to the pedicel, was from 1:2 to 1:8. The ratio was high in easily shedding varieties and low in persistent varieties. 2. Highly positive correlation (0.969) was obtained between the breaking tensile strength and the breaking bending strength. From the result, it is thought that the hardness of grain shedding is expressed sufficiently only by the mean value of the breaking tensile strength. 3. The breaking tensile strength of a grain was stronger in lower portion than in upper portion in a ear. Accordingly, average breaking tensile strength of a number of grains on each primary rachilla was somewhat stronger in that of lower portion than in that of upper portion in a ear. However, relationship between the strength of a grain shedding and earliness of the flower open was not observed. Average breaking tensile strength of a number of grains in upper three primary rachillas was nearly the same with that of all grains in the ear. 4. Degree of grain shedding character have been usually classified into 6 classes for convenience, i. e. persistent, little persistent, medium, little easily shedding, easily shedding and most easily shedding, respectively. The breaking tensile strength of rice verieties in this experiment belongs to each groups were as follows: persistent; 235-160 g, little persistent; 210-155 g, medium; 210-150 g, little easily shedding; 150-90 g, easily shedding; 170-90 g and most easily shedding; 115-75 g, respectively.
