Agriculture Reference
In-Depth Information
light to give a R:FR underneath of 2.73 as opposed to 1.22 under clear film or
1.28 in the open, the plants under the FR film did not bulb (see Fig. 4.45).
Bulbs planted in the autumn were only slightly delayed in bulbing under
FR filters, whereas summer plantings were strongly inhibited from bulbing
(Yamazaki,
et al.
, 1998). Subsequent experiments (Yamazaki
et al.
, 2002)
showed that cool-temperature storage (5°C rather than 25°C for 70 days) of
summer-planted bulbs lessened the bulb-inhibiting effect of high R:FR. This
suggests that the cool temperatures following autumn planting decrease the
inhibition of bulbing by high R:FR, as well as decreasing the photoperiod
needed for bulb induction. Plastic film tunnels that increase R:FR can usefully
extend the period of green leaf production in summer-planted
A.
wakegi
by
preventing bulbing (Yamazaki
et al.
, 2000).
Bulb development in
A.
wakegi
is associated with an increase in abscisic
acid (ABA) concentration in the bulb tissue and a decrease in the water
potential and solute potential in the bulb scales (see Fig. 4.46). During bulb
storage ABA concentration and depth of dormancy, as measured by days to
bulb sprouting after planting on moist vermiculite, decrease in parallel from
bulb harvest in late May until planting in early October (see Fig. 4.46).
When fluoridine, an inhibitor of ABA synthesis, was applied to plants
during bulb formation, the resulting lower ABA content was correlated with
faster sprouting (Yamazaki
et al.
, 1999a). Therefore the depth of dormancy
correlates with ABA concentration in the bulb. However, the decrease in ABA
concentration induced by fluoridine did not prevent bulbing, suggesting that
ABA does not itself induce bulbing.
Cultivars differ in bulb dormancy. Cv. 'Ginoza' accumulates ABA during
bulb formation but does not become dormant. On planting in moist conditions
Fig. 4.45.
The prevention of bulbing in
Allium
wakegi
by increasing the red:far-
red ratio (RFR) of light. Plants grown under plastic film with much reduced
transmission of far-red wavelengths (left), plants bulbing under clear plastic film
(centre) and plants bulbing when grown without a film cover (right) (from Yamazaki
et al
., 2000. Courtesy of
Journal of the Japanese Society for Horticultural Science
).
