Abstract
In cereal crops uniformity of heading time of the tillers within a variety, or synchrony of heading, is necessary for simultaneous ripening. On the other hand, to avoid the environmental stress at anthesis, excessive synchrony of heading is not desirable. Thus, a proper level of synchrony in a variety ought to be achieved by breeding. In this study synchrony of heading in 60 Japanese rice varieties (Table 1) has been analysed in relation to their earliness and panicle number. However some of the very early varieties, designated as 'VE' in Table 1, were excluded from statistical analysis, because those main culms showed unexpectedly early heading in comparison with the other tillers in respective plants (Figure 2). Four or eight plants of each variety, grown in pots were placed in a glasshouse, and synchrony of heading was evaluated with these materials. Five plants of each variety were also grown in a paddy field to investigate their agronomic traits. Regression coefflcient of heading date of each tiller on the order of heading, which had been deflned as the synchrony index by PARODA (1971) was not a suitable indicator of the synchrony of heading when the number of panicles showed significant variations (Table 3). Therefore, synchrony of heading was expressed by the standard deviation of heading date of individual tillers within each plant.
