Genetic characteristics of circadian flowering rhythm in Hemerocallis

Abstract

An environmentally synchronized circadian clock is important for plant growth and developments. In the genus Hemerocallis, plants can be divided into diurnal (open between 3:00-15:00) and nocturnal (open between 15:00-3:00) flowering. The duration of each single flower is no more than 24 h. Hybrids obtained through crossing between diurnal and nocturnal flowers are fertile and show different daily flowering rhythms from their parents. Therefore, to enhance our understanding of daily circadian flowering rhythms in Hemerocallis, we studied inheritance by observing flowering processes among species, cultivars and F1 hybrids. Daily flowering rhythm was a relatively stable character that could be influenced through a breeding program. In F1 generations of crosses between daylilies and nightlilies, there was an obvious tendency toward nocturnal opening. Opening times showed a negatively skewed and leptokurtic distribution with a single peak. Closure times showed a normal distribution (peak times were 12:41–13:53, almost the mid-parent value). Variation increased when cultivars were used as parents, especially in closure times. Observations over 4 years showed subtle differences with a similar trend.Our results suggest that in Hemerocallis, opening is characterized by mixed major loci and polygenic inheritance, with dominant nocturnal opening. Closure was controlled by multiple genetic loci. Inheritance of opening and closure is controlled by different nuclear circadian clock genes and perhaps photoreceptor-binding motifs. By manipulating cultivar diversity, single flower duration could be prolonged effectively through hybridization. In addition, it was assumed that daily flowering rhythm was not a completely conserved character, and could be partly affected by environment.