Opposite response groups of short-day plants to the spectral composition of the main light period and to end-of-day red or far-red irradiations

Two response groups were found among short-day plants grown in blue green-houses having a high or low far-red admixture. In one group flowering was promoted by low far-red and delayed by high far-red; the other group reacted in an opposite manner. In plants grown under 8-hr day and 16-hr night regimes, flowering in the low far-red group was promoted by red and inhibited by far-red illumination preceding the 16-hr nights; in the high far-red group flowering was promoted by far-red and inhibited by red illumination preceding the dark periods. In both groups flowering was inhibited by red light applied in the middle of the dark period.