Control of Growth and Reproduction in Cultivated and Wild Rice by Light Quality and Dark Period

Abstract

One cultivated and two wild rice varieties have been subjected to variation in photoperiod and light quality by daily exposure of the seedlings at the four-leaf stage to 8 h of natural daylight followed by white incandescent, red, green or blue light for 2,4 or 8 h in a temperature and humidity-controlled growth chamber. In some cases far-red irradiation was applied after white or red for 1 and 2 h. The treatments caused marked differences in growth and reproduction between the cultivated and wild rices. The cultivar Dudkalmi showed extensive tillering after far-red exposure. Earliest flowering was observed with a 16-h dark period both in the cultivated and wild rices. Failure of flowering with and 8-h day and 8-h artificial light of different wavelengths could be overcome by red or far-red of 1-h duration. The light quality interacted differently with the dark period in the acceleration of flowering in the three varieties. In another experiment the effects of interruption of the dark period by a light period of 2 h after from 4–12 h of darkness in a 24-h cycle were studied in the two wild rice varieties. Light of different wavelengths interposed in the dark period caused variation in tiller number and stem length in comparison to an uninterrupted dark period of 16 h. The effect at the beginning of the dark period was earlier flowering; flowering was delayed by interruption at 4 h and inhibited after 8 h but accelerated after a 10- to 12-h dark period. The results are discussed in the light of the significance of the dark period and light quality in regulating hormone balance and phytochrome reactions.