NATURAL FLOWER INITIATION IN SPATHIPHYLLUM: INFLUENCE OF DAY LENGTH AND LIGHT INTENSITY

Over a period of approximately 3 years, 10 standard greenhouse cultures of Spathiphyllum ‘Alfa’ were set up in order to determine the influence of altering climatic conditions in different seasons on the flowering process. In every culture, the start of flower initiation of ‘Alfa’ was accompanied with non-elevated day temperatures (20-24°C), short(ening) photoperiod (<12h), dropping or low light intensities; resulting in light sums between 1.5 - 5.4 mol x m^-2 x day^-1. In a growth room experiment the influence of photoperiod (16h and 8h) and light intensity (110 and 55 μmol x m^-2 x s^-1) was further investigated. This experimental set up resulted in 3 different light sums: 6.3/3.2/1.6 mol x m^-2 x day^-1. The daily light sum of 3.2 mol x m^-2 was given both under short and long day. Flower initiation was hastened by short day (facultative requirement) but the effect of photoperiod was influenced by light intensity. Probably this interaction between photoperiod and light intensity was mediated through the obtained light sum. Photoperiod had no significant effect on vegetative growth, which was only influenced by the light sum. The treatment with the highest light sum (LD –110 μmol x m^-2 x s^-1) resulted in a more abundant vegetative growth, which counteracted the generative development and delayed the start of flower initiation. The direct effect of light sum on vegetative growth resulted also in an indirect effect on generative development of ‘Alfa’.

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