Varietal Variation in Photoperiodic Response, Chilling Requirement and Narrow-Sense Earliness and their Relation to Heading Time in Wheat (Triticum aestivum L.)

Abstract

Heading time in the field of fall-sown common wheat varieties and three heading traits, i.e. photoperiodic response, chilling requirement and narrow-sense earliness, were examined, using 158 local wheat varieties collected from various countries. And their relationship was analyzed for investigating how these traits interacted to control heading time in the field. Wide varietal variation was observed in each heading trait as well as in heading time Itself. Correlation coefficient between narrow-sense earliness and two measures of photoperiodic response, which was calculated as the difference in or as the ratio of growth period under long-day and short-day conditions, was higher in the former (r = .724) than In the latter (r=.588). The existence of such difference (P0.05) indicated that photoperiodic response measured as the difference partly depended on narrow-sense earliness, and that photoperiodic response should be measured as the ratio. Though simple correlation coefficient calculated between heading time and chilling requirement was positive and statistically significant, partial correlation coefficient was statlstically insignificant. In addition, almost whole variation in heading time was covered by varieties belonging to only one chilling requirement class, that is, O days. These facts clearly indicated that chilling requirement was not important for the control of heading time, but for the adaptation to winter coldness. On the other hand, partial correlation coefficients of photoperiodic response and narrow-sense earliness on heading time were statistically significant (P0.01), indicating that both traits took part in controlling heading time. It was also concluded that narrow-sense earliness was as important as photoperiodic response, though this trait was formerly considered as minor factor for the control of heading time. And the mechanism to control heading time seemed to be different between these traits. Therefore narrow-sense earliness as well as photoperiodic response should be taken into account for the selection for heading time in wheat.