Inflorescence and Flower Development in Musa velutina H. Wendl. & Drude (Musaceae), with a Consideration of Developmental Variability, Restricted Phyllotactic Direction, and Hand Initiation

Abstract

Premise of research. Inflorescence and flower structure in the Musaceae is unique in the Zingiberales. The inflorescence lacks the obvious cincinnus structure that characterizes the order, and the flowers are unisexual. Previous studies were conducted using cultivated varieties and were carried out with sectioned material, which does not permit accurate developmental descriptions. Developmental study of a wild species with modern methods addresses these shortcomings and provides more accurate descriptions. Methodology. Young inflorescences and flowers were collected from botanical gardens in Hawaii and Australia and critical-point dried for observation with a scanning electron microscope. Pivotal results. All shoots and inflorescences have sinistrorse (left-handed) phyllotaxy, and the sequence of flower initiation is usually correlated with this pattern. Initiation begins on the cathodic side of the hand (opposite the direction of phyllotactic rise) and progresses anodically (in the direction of phyllotactic rise). Within this general pattern, the sequence of flower initiation is variable, even within the same inflorescence. Five patterns of initiation are reported, with additional variation within each pattern. Both male and female flowers have similar early developmental patterns but diverge at the time of petal/inner androecial formation. In male flowers the anterior side of the flower develops slightly ahead of the posterior, while in female flowers the posterior side develops slightly ahead of the anterior. While consistently present in the material analyzed here, these differences are not apparent at the time of gynoecial initiation or in the mature flowers. Conclusions. The banana inflorescence is another example of how higher-level phyllotactic patterns can influence the sequence of organ initiation at lower levels. Despite variability in the sequence of flower initiation in a hand, the best interpretation of the hand remains a cincinnus. Variability in inflorescence and floral development is rarely reported and may be more common than currently supposed.

Overcoming the fertility crisis in bananas (Musa spp.)

“…In the early stage of inflorescence development, the female and male flowers are morphologically almost indistinguishable, with gynoecial (pistils) and androecial (stamens) parts of the flower developing in both, although with subtle differences in the pattern and the size of organ development (Kirchoff, 2017). Ultimately, however, whether the mature flower is female or male is not due to small differences in the pattern of organogenesis but rather is concerned with the size and fertility of the gynoecium and androecium in the flowers (Kirchoff, 2017).…”

“…In the early stage of inflorescence development, the female and male flowers are morphologically almost indistinguishable, with gynoecial (pistils) and androecial (stamens) parts of the flower developing in both, although with subtle differences in the pattern and the size of organ development (Kirchoff, 2017). Ultimately, however, whether the mature flower is female or male is not due to small differences in the pattern of organogenesis but rather is concerned with the size and fertility of the gynoecium and androecium in the flowers (Kirchoff, 2017). By the time the developing inflorescence is about halfway up the pseudostem, the ovaries of female flowers have become longer than those of the male allowing female flowers to be distinguished from male Figure 1 Key pre-and post-fertilization processes in reproductive biology, leading to success or failure in producing a seedling.…”

“…Musaceae are grouped taxonomically within the Zingiberales by their androecium, which is described as non-petaloid with 5-6 stamens (Simmonds, 1962). Typically, the male flower of Musa species has five polliniferous stamens (Kirchoff, 1992), three in an outer stamen whorl and two in the inner whorl around the gynoecium, with the posterior stamen of the inner whorl absent (Kirchoff, 2017). The filaments are free and stiff, and the anthers are bilobed and tetrasporangiate.…”

“…For a further detailed discussion on reproductive biology in Musa, see Fortescue and Turner (2011); for detailed anatomical studies of floral organogenesis in M. velutina, M. ornata and the triploid edible cultivar 'Go Sai Yung', see Kirchoff (1992) and Kirchoff (2017). For a functional approach to bunch formation including the occurrence of hermaphrodite flowers, see Turner and Gibbs (2018).…”

“…Pollination and subsequent fertilization of the ovules in the fruit are crucial processes in producing viable seeds. Knowledge of reproductive biology and breeding systems of bananas has progressed considerably although in-depth studies on flower development are limited to only a few banana cultivars (Fortescue and Turner, 2011) or Musa species (Kirchoff, 2017). Understanding the specific morphological, physiological and environmental factors surrounding the processes responsible for effective pollination, fertilization and viable seed production as well as identifying and overcoming possible barriers to these processes are essential for successful banana breeding.…”