Effect of age at initiation of short-day treatment on earliness to flower in three Stylosanthes guianensis genotypes

Abstract

The number of days from planting to flowering and number of short-day (9 h) cycles to flowering of three Stylosanthes guianensis genotypes were evaluated on seedlings grown for 0, 4, 8, 12, or 16 weeks under natural (approximately 12 h) photoperiod before the start of the short-day treatment. Untreated controls grown continuously under the natural photoperiod were included. All genotypes responded to short-day treatment, flowering earlier than the controls. Differences among genotypes in number of days to flower and in number of short-day cycles to flower under each treatment were found. The number of short-day cycles to flower decreased with increasing age at the start of the short-day treatment, indicating an initial, non-receptive juvenile period. The duration of the juvenile period differed with genotype and was prolonged under short photoperiod. Differences among genotypes in the duration of the juvenile period were not related to differences in growth rate as measured by main stem length. The plant age at the start of short-day treatment that resulted in minimum time to flower ranged among genotypes from 4-1 2 weeks. Initial plant growth under long, non-inductive photoperiod at photosynthetic light intensity with subsequent short-day treatment should decrease time to flower for short-day types of S. guianensis, resulting in a decrease in generation time of glasshouse-grown plants.