Variation of flower opening and closing times in F1 and F2 hybrids of daylily (Hemerocallis fulva; Hemerocallidaceae) and nightlily (H. citrina)

In flowering plants, pollination success is strongly dependent on the timing of when flowers start to bloom and when they start to close. To elucidate the genetic mechanism influencing the timing of flower opening and closing, we obtained F1 and F2 hybrids of Hemerocallis fulva (a diurnally blooming species, pollinated by swallowtail butterflies) and H. citrina (a nocturnally blooming species, pollinated by nocturnal hawkmoths) and observed their flowering behavior from blooming to closing with the use of digital cameras. For flower opening times, F1 hybrids were highly variable, and F2 hybrids showed a bimodal distribution of flower opening times with peaks in both the morning and evening. The ratio of morning flowering and evening flowering among F2 hybrids did not deviate from 1:1. For the start to close time, both F1 and F2 hybrids were similar in showing the major peak in the evening. The ratio of evening closing and morning closing among F2 hybrids did not deviate from 3:1. These results suggest that the time of flower opening and the start of closing are regulated by different major genes.