Diversity in flower morphology of the single-type tuberose (Agave amica (Medik.) Thiede & Govaerts)

Tuberose [Agave amica (Medik.) Thiede & Govaerts] is a tropical bulb grown commercially for its sweet-scented flowers and highly valued essential oil. In this study, the floral morphologies of 18 tuberose genotypes were studied to understand their diversity and compatibility (for selfing and crossing) so that prerequisites for parental selection can be established. The genotypes—all of which had single florets—varied significantly in terms of floret length, floret diameter, tepal thickness, number of tepals, and stamen length. The flowers opened in the evening, and anther dehiscence occurred within 20–30 min of anthesis. The styles showed three distinct morphological types in terms of the relative positions of the stigma and the upper or lower ends of the stamen, as follows: L-morph, for long styles, if the stigma was located above the upper end of the stamen; S-morph, for short styles, if the stigma was below the lower end of the stamen; and I-morph, for style of intermediate length, if the stigma was positioned somewhere in between the upper and lower ends of the stamen. Stigma receptivity increased gradually, whereas pollen viability declined slowly from the 1st to the 4th day of anthesis. Self-compatibility, self-incompatibility, and sterility were confirmed via autogamy, geitonogamy, and controlled pollination. In ‘Arka Prajwal’, the pollen tube entered the ovule 24 h after pollination and the female gametophyte developed up to 5 days after pollination. However, the embryo sac began to degenerate from the 7th day of pollination and the pods were shed, which confirmed the sterility of the ovule. This comprehensive study of floral morphology is expected to provide useful insights for breeding tuberoses of superior flower quality and improved yield of the essential oil.