Agriculture Reference
In-Depth Information
Reproductive Biology
Inflorescence and Bunch Development
After the early differentiation of some 25-50 leaves, the development of which is
dependent on cultivar and environmental conditions, the apical growing point at the
base of the pseudostem ceases to produce leaves and starts to develop an inflores-
cence. The transformation of this process is neither externally visible nor are there
any other characteristic signs of flower initiation. The nature of the flowering stimu-
lus is unknown and probably not related to temperature or photoperiod, although
the latter factor may play some role (Turner and Fortescue
2012
). The trigger for
flower initiation could be hormonally induced with gibberellic acid (GA
3
) involved
in the process, but this hypothesis still has to be tested and verified. The anatomical
and morphological changes occurring during flower initiation in banana, as well as
other pertinent aspects related to the reproductive biology, have been summarised
by Robinson and Galán Saúco (
2010
).
Flower initiation starts when the apical meristem rises into a dome that shows in-
tense mitotic activity. This activity immediately ceases when the leaves are replaced
by flower bracts; the first to emerge are the female bracts and later the male bracts.
All bracts enclose axillary, crescent-shaped meristematic “cushion” from which the
flowers differentiate. There is not clear morphological distinction between male
and female flowers until the inflorescence is about 120 mm long and some 1.5 m
from the base of the pseudostem. The inflorescence, a complex spike, consists of a
stout peduncle on which the flowers are arranged in nodal clusters with each node
comprising normally two rows of flowers set on transverse cushions, and subtended
by a bract that protects the young flowers. The flowers are grouped in clusters with
their bracts born spirally but do not completely encircle the peduncle. There may be
from 5 to 18 basal (proximal) nodes bearing female flowers. By contrast the upper
(distal) nodes contain male flowers and remain tightly enclosed in bracts that form
a conical structure called the 'bell'. In between both flower types are some nodes
containing hermaphrodite flowers with short ovaries that, as in the case of the male
flowers, do not develop into edible fruits and, in most cultivars, abscise at an early
stage after flower emergence.
The developing flower stalk (peduncle) rises inside the pseudostem until it forc-
es the inflorescence to emerge through the top or 'neck' of the plant, the latter being
formed by the petioles of the last few leaves to emerge. At the moment of flower
initiation, 10-12 leaves are still inside the pseudostem and emerge progressively at
the neck while the inflorescence moves upwards. At emergence the inflorescence
is initially erect but quickly points downwards due to its own weight and the con-
tinued growth of the peduncle. After emergence, the bracts, that cover the double-
layered female nodes (commonly called 'hands') and tightly packed fruit, rise and
remain exposed. In banana (
Musa
AAA) cultivars the bracts roll back at their tips
and progressively dry out and drop off during early bunch development. The bracts
and flowers in their axils open in proximal to distal sequence while the peduncle
continues elongating from the meristems ending in the male bell. Within a few
