Agriculture Reference
In-Depth Information
Dormancy in Japanese cultivars of Chinese chive is triggered by exposure to
photoperiods of 14 h or less for 30 days. Subsequent exposure to long periods at
low temperature breaks the dormancy and permits regrowth as temperatures
increase (Saito, 1990).
Chinese chives require long photoperiods in order to bolt. The critical
photoperiods needed are longer for Japanese cultivars than for strains from
southern Asia (Saito, 1990). Many cvs will not flower in the first year after
sowing, indicating that a period of cool induction may be needed after the
plants have reached a critical size.
All the edible alliums grown from seed are similar in having slow germination
and emergence rates and low relative growth rates in comparison with other
crop species. This, along with their erect, narrow leaves, makes them vulnerable
to suppression by faster-growing weeds over a long period of early growth (see
Chapter 5, 'Effects of weed competition'). If they are planted as bulbs (sets or
cloves) rather than seeds, the larger propagule makes for easier and faster crop
establishment.
In those species that can form bulbs and inflorescences there are striking
similarities in the environmental control of these two developmental pathways.
Long photoperiods stimulate bulbing, the later stages of flowering when the
scape is elongating and sometimes the earlier stage of inflorescence initiation.
Light spectral quality as characterized by red:far-red (R:FR) ratio modifies the
photoperiodic effectiveness of light in stimulating bulbing. The lower the R:FR in
an inductive photoperiod the faster the bulbing, and the minimum photoperiod
for bulb induction increases as R:FR increases. Direct R:FR effects on flowering
have not been reported, but high plant densities, which cause low R:FR under
the leaf canopy, can increase flowering (percentage of plants bolting) (Bosch-
Serra and Domingo-Olivé, 1999), indicating there may be a promotive effect of
low R:FR on inflorescence induction or scape elongation.
With stored bulbs, and sometimes growing plants, a period of cool
temperatures (5-13°C) can accelerate subsequent bulbing. Extended periods
at such temperatures are necessary for inflorescence induction (i.e. for
vernalization). Periods of warm temperature (25-35°C) applied to bulbs of
onion, shallot and
A.
wakegi
immediately after cool treatment nullify bulbing
acceleration. Extended periods at such temperatures reverse inflorescence
induction and have a devernalizing effect (see Fig. 4.39). Examples where
flowering has diverted into bulbing are seen at many points along the route of
inflorescence development (see Fig. 4.35; Kamenetsky
et al.
, 2004). First, there
are the withered young inflorescences seemingly squashed by an adjacent bulb
