Mechanism of deleyed development on young panicle in sorghum varieties

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1. Greenhouse experiment were conducted to clarify the interactions of temperature and photoperiod. From the results for Ryuujinwase (photosensitive variety), the minimum duration of panicle initiation (emergence to young panicle initiation stage) was observed by 22-24ﾟC in long daylength (16hrs) condition.2. The period of panicle initiation was varied with diurnal temperatur change conditions (24(]SY.+-。[)0-24(]SY.+-。[)6ﾟC), and there was high correlation coefficient between the duration of panicle initiation and effective accumulate temperature (critical temperature ; 22ﾟC).3. From the results of short daylength treatments (12hrs ; 3,6 and 9 days) before panicle initiation time in field conditions using some varieties, the durations of BVP (basic vegitative phase) of varieties were estimated ranging from 3 to 9 days, and the durations of BVP were reduced by hifh temperature. And also, the durations of PSP (Photo sensitive phase) were estimeted ranging 3-6 days, and the durations of PSP were increased at temperature above 22-24ﾟC.4. This study confirmes the necessity to divide the entire pre-initiation period into the two phases for accurate estimation model for heading time in sorghum varieties. Futher studies are needed to elucidate the phenomon in some photo-sensitive cultivars of the deleyed heating by high temperatures.