Relation of Number of Spikelets per Panicle to the Characteristics of Shoot and the Size around Growing Point at Panicle Initiation Stage in Rice Varieties

Abstract

The relationships between number of spikelets per panicle and the characters of shoot and the size around growing point at panicle initiation stage were studied with the rice varieties bearing much different number of spikelets from 1989 to 1991 in a paddy field, aiming to clarify the mechanism of varietal difference in number of spikelets per panicle. The number of spikelets per primary rachis branch, internode diameter (especially the first internode from top) and panicle length had positive linear relationships to number of spikelets per panicle on main stem in each year. These relationships of number of spikelets per panicle on main stem to number of spikelets per primary rachis branch and the first internode diameter were well applicable to all tillers, irrespective of varieties and years. The diameter of young panicle base in panicle initiation stage, assumed to be the size around growing point, on main stem was positively related to number of spikelets per panicle and the first internode diameter closely. Number of spikelets per panicle is assumed to be the same when diameter of young panicle base is the same in all varieties studied, even though the varieties have less endogenous gibberellins. Therefore, it is concluded that diameter of growing point at panicle initiation stage plays a very important role in determination of the number of differentiated spikelets per panicle through number of spikelets per primary rachis branch, and causes varietal difference in number of spikelets per panicle.