AbstractStem apices of 78 sugarcane varieties were examined microscopically to determine the precise date of flower initiation during the 1967 and 1969 flowering periods at Gurabo Substation, P.R. A stage method for measuring floral initiation was developed and adopted. It was found that flower initiation or the formation of flower primordial is not simultaneous among all varieties of sugarcane. Initiation time was found to vary from September 1 to September 30. The model day-length for floral initiation in Puerto Rico (latitude 18° N.) appears to be 12 hours, 7 to 17 minutes. Both time of initiation and speed of inflorescence growth and development was found to be related to the time of flowering. The time required for the development and elongation of inflorescences was from 7 to 10 weeks in 90 percent of the varieties. The time of initiation in respective varieties is fairly constant from one year to the next. This indicates that flower initiation in sugarcane is determined primarily by photoperiod. However, as indicated in these studies, both low temperature and moisture stress were regarded as important factors in delaying the time of flower initiation. Moisture stress during 1967 appeared to be the predominant factor causing significant delay in the time of tassel emergence among the majority of varieties studied.
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