Effects of Night Breaks on Floral Initiation and Development in Saccharum1

Abstract

The effects of night breaks with light of different spectral compostion applied at various stages of floral development, starting before induction up to inflorescence emergence, were studied in Saccharum spontaneum L. and S. robustum L. clones. Night interruption treatments with incandescent light decreased % inflorescence emergence and delayed flowering when applied at all stages of development in S. spontaneum L. In both S. robustum L. and S. spontaneum L. clones, the degree of inhibition of flowering depended on the stages of development at which the night interruptions were applied; the early stages of differentiation of the inflorescence (initiation of inflorescence axis and branch primorda) were found to be the most sensitive. The spectral composition of the light used was also important; red, orange, and green light were generally the most inhibitory to inflorescence development, while blue, far‐red, and ultraviolet were not effective and similar to darkness. Attempts to reverse the inhibitory effect of red light by far‐red failed. Night breaks also had their maximum inhibitory effects when applied towards the end of the dark period and had minimum effects when applied at the middle of the dark period.