Agriculture Reference
In-Depth Information
(see Fig. 4.38), then there are examples of one or a few bulbs forming on
partially elongated scapes and finally there are fully emerged inflorescences
carrying numerous bulbils that have developed by suppressing the developing
florets (see Fig. 2.18e, f, g and Fig. 4.41) or after deliberately removing the
florets. It seems likely that generations of selection for bulbs, which constitute
an easily harvested and stored source of food and an easily cultivated
propagule, have favoured bulbing in garlic and shallots to the extent that
flowering and seed production is eliminated in some strains, and in other
cultivars flowering can be induced only by a very precise sequence of
environments each specific to a particular phase of floral development
(Kamenetsky
et al.
, 2004; Esnault
et al.
, 2005).
There seems to be fine balance between the path of inflorescence develop-
ment and bulb development, with warmer temperatures tending to favour the
latter, although this depends on the stage of inflorescence development, as after
the stage of floret development warm conditions can favour rapid progress to
anthesis and seed ripening. What constitutes a long photoperiod and low
temperature will vary with cultivar and the climate to which it is adapted, so
we can only describe trends in bulbing and flowering responses to these
variables. The absolute values of photoperiod and temperature needed to
progress flowering or bulbing at a particular stage of development will be
specific to a particular cv. and similar for other cvs adapted to the same or
similar region.
In view of these similarities in the control of flowering and bulbing and the
easy switching between the two developmental paths, it is interesting to
consider how this connection evolved. It seems likely that bulbing can give a
plant a better chance of survival if climatic conditions deteriorate such that
flowering will not result in seed production. It also allows slow-growing plants
like alliums to reach a size large enough for flowering in environments with a
short growing season. Is it possible that bulbing evolved as a deviant or
diverted flowering response? Do the same genes control the similar responses to
environment of both developmental paths?
