Agriculture Reference
In-Depth Information
Cultivated hybrids of
Allium cepa
A number of onion types are hybrids between
A. cepa
and
A. fistulosum
,
including the 'top onion' (also termed 'tree onion', 'Egyptian onion' or
'Catawissa onion'), which produces small bulbs (termed 'bulbils' or 'top-sets')
instead of flowers on the inflorescence (see Fig. 4.41). These have been termed
Allium
proliferum
(Fritsch and Friesen, 2002). The bulbils sometimes sprout
on the inflorescence, and both dormant and sprouting inflorescence shoots
may be eaten and are also used to propagate the plant. Top onions are a home
garden crop that used to be popular for early spring green onion production in
the USA (Jones and Mann, 1963). They are also grown as home garden crops
in Europe and north-eastern Asia (Fritsch and Friesen, 2002). They are seed
sterile, and molecular methods have confirmed their hybrid parentage (Klaas
and Friesen, 2002).
The Wakegi onion (
Allium
wakegi
) is a diploid hybrid (chromosome
number 16) between
A. fistulosum
and a shallot-type
A. cepa
. It has been grown
for centuries in Japan and China as a green salad onion crop (Inden and
Asahira, 1990). It produces slender leaves 60-70 cm long and it divides freely
to form many side shoots (tillers). Unlike true
A. fistulosum
, it forms bulbs in long
day-lengths and it becomes dormant in summer. It is not very cold hardy and is
grown in the warmer regions of Japan. Molecular and chromosomal studies
have confirmed the hybrid parentage. The DNA of the chloroplasts from
Japanese material hybridized with
A. fistulosum
complementary DNA, indicat-
ing that the cytoplasm derived from Japanese bunching onion, and therefore
this species was the maternal parent. However, in different lines from Indonesia,
analysis of chloroplast DNA indicated that both shallot and bunching onion
were maternal parents, indicating multiple origins for this type of hybrid.
Hybridization between a common onion type and
A. fistulosum
gave rise to
the variety 'Beltsville Bunching', which is grown as a green bunching onion,
and which has the resistance to pink root disease characteristic of
A. fistulosum
.
Hybrids involving shallots and
A. fistulosum
have produced the non-bulbing
'Louisiana Evergreen' and the bulbing, shallot-like 'Delta Giant', both of which
are pink root resistant (see Chapter 5).
A more slender hybrid species (
Allium
cornutum
) - known as 'Pran' in
Kashmir and shown to be identical with the Croatian cultivar 'Ljutica' - is a
triploid in which
A. cepa
is the donor of two sets of chromosomes, but the origin
of the third set remains unclear. It is quite widely distributed as a garden crop
in Tibet, Jammu, Europe and Canada (Fritsch and Friesen, 2002).
Edible alliums of lesser or local importance
Many wild species of alliums are used by local inhabitants, particularly in the
republics of central Asia, western China and southern Siberia, and the list of such
