Studies on the Physical Characteristics of Rice Seedlings : II. The varietal difference on physical characteristics of rice seeflings

Abstract

To obtain the information on varietal difference, physical characteristics were measured with the seedlings of fifteen rice varieties (including two upland and two glutinous varieties), grown at two seeding rates for different periods. 1. Varietal difference was significant in most of the physical characters tested (i.e. buckling moment, section modulus, buckling stress, buckling index, deflection ratio, and plant height). Significant correlation coefficients were found between the degree of lodging resistance and some of physical characters of seedling (i.e. section modulus, buckling index, and plant height). This means that seedlings of varieties highly resistant to lodging are mostly short in plant height, thick in basal section, elect in plant type, and possess the high resistance to buckling. Varieties of high resistance to lodging are also prefarable and recommended for mechanical transplanting. 2. Seedlings of glutinous rice varieties and upland rice varieties possess specific physical characteristics. In comparison with lowland nonwaxy rice, buckling moment is bigger due to bigger section modulus, buckling index and deflection ratio are higher. All of these characters are considered unfavourable for mechanical transplanting. 3. Physical characteristics of seedlings grown under high planting density or for a longer period were closely related to those grown under low planting density or for a shorter period, respectively. This suggests that the physical characteristics of seedlings are hardly affected by the changes of planting density and growing period. 4. With reference to the results mentioned above, the authors are led to expectation of the possibility of successful breeding of rice varieties suited for mechanical transplanting