Abstract
Early maturity has been one of the major breeding objectives in wheat (Triticum aestivum L.) in the south-western part of Japan, because this trait is desirable for double cropping with summer crops such as rice, and for avoiding pre-harvest sprouting which often occurs in the rainy season. However, early maturing cul-tivars usually belong to the spring type which is ptone to frost damage in early sprin.g because of the earliness in ear primordia initiation and stem elongation. The relationship between ear primordia initiation, young Panicle length, stem elongation and heading traits, i.e. vernalization requirement, photoperiodic response and narrow-sense earliness, was assessed for 32 cultivars and lines. Date of the beginninb" of stem elongation, which was defined as the time when the main stem length reached 20 mm, and young panicle length at that time were estimated using an, exponential curve based on the records made at an interval of two weeks.
