Agriculture Reference
In-Depth Information
Growth and bulbing
The growth pattern of garlic is similar to that of onions grown from sets. Many
of the physiological responses of garlic to environment are also similar to those
of onion. Takagi (1990) reviewed the physiology of garlic, and papers by Mann
and his colleagues (Mann, 1952; Mann and Lewis, 1956; Mann and Minges,
1958) describe extensive physiological and agronomic trials on garlic in
California, the state that accounts for most of US production. This account is
based primarily on these sources.
Where garlic is a major crop it is planted in the autumn or early winter and
grown through to bulb harvest in the early summer. In California, planting dates
range from September to March depending on location, variety and desired
maturity date, but the common planting dates are October-November for cv.
'California Early' and November-January for cv. 'California Late'. Garlic is
extremely hardy and can withstand considerable frost, but in areas with severe
winters it must be planted in spring. In California the crop produces leaves and
increases in height until May-June, reaching a maximum 10-12 visible leaves
per plant and a height of 75-90 cm. Bulbing commences in late April, first with
some swelling of the bases of the leaf blades and then with the swelling of the first-
formed (outermost) cloves. Cloves continue to initiate in the axils of the inner
foliage leaves (see Fig. 2.11) as bulbing progresses. A maximum of about 20
cloves per plant is typical of California garlic at harvest. Bulbing ratios increase
from about 1.2 in vegetative plants to 5 or more when the plants mature.
Physiological studies under controlled conditions using Japanese strains
that normally bolt and produce multi-cloved bulbs in the field have shown that
a garlic clove may develop along several paths, depending on the sequence of
environmental conditions to which it is exposed, its genotype and its size
(Takagi, 1990). In certain conditions neither bulbing nor flowering may occur,
and plants may make indefinite vegetative growth. Various degrees of bolting
can occur, ranging from a vestigial flower stalk within the bulb to a fully
developed flower stalk and umbel. In these strains, inflorescence induction
seems to be a prerequisite for the formation of normal, multi-cloved bulbs.
Extremely rapid bulbing results in a single clove at the shoot apex, with no
lateral buds forming before clove development and no inflorescence development.
Single-cloved bulbs tend to be produced by small plants grown from small cloves or
top-sets. If bulbs are stored at 2-4°C for 6 months or more, secondary bulb (clove)
initiation may occur at the shoot apex actually
within
the stored bulb, an extreme
that has also been observed in onion. The occurrence of all these developmental
routes is subject to the influence of temperatures in storage before planting and to
temperatures and photoperiods after planting.
Bulbing is stimulated by long photoperiods, warm temperatures and light
of low red:far-red ratio, just as with onion. But, at least in temperate varieties,
