Effect of Light Condition and GA3 Application on Development of Axillary Buds during Cooling Treatment in Phalaenopsis.

Abstract

Effects of light exposure versus dark with and without GA3 application during a 20°C treatment on development of axillary buds in Phalaenopsis were investigated.In the light-20°C treatment, the days to spiking from beginning of temperature treatment were 21.3 days. No buds on plants held at 20°C in the dark spiked after 36 days but when transferred from the dark to the light, they spiked 18.6 days later. The application of GA3 in dark did not substitute for light to induce bud emergence. Consequently, we conclude that spiking of Phalaenopsis requires exposure to 20°C and also light.The axillary buds had 4 to 5 bract leaves before the 20 °C treatment was imposed, but no lateral bud existed within the bracts. After 21 days at 20 °C, spiking have already begun, and bract leaves thickened and elongated. Differntiation of a lateral bud also occurred between the apical meristem and the inner bract leaf. These responses failed to occur in the dark with or without GA3 application. This suggests that development and elongation of axillary buds do not occur under dark condition, the initial reaction for spiking requires light; and GA3 may not participate in the process.The sugar contents of the spiked plants in the light-20°C treatment increased, but those of the non-spiked plants in the dark decreased significantly, compared with those at the begining of treatments. However, there was little difference in the number of days to spiking from onset of light exposure between the treatments. Therefore, it seems that the suppression of spiking in the dark can not be attributed solely to the reduction in sugar contents.