Agriculture Reference
In-Depth Information
(a)
Fig. 3.6.
Pollination control in onion breeding.
(a) Onion umbels massed for cross-pollination within
an insect-proof pollination 'cage' with nylon mesh
walls. (b) Umbel enclosed by cellophane bags
containing blowflies to ensure self-pollination
(photographs courtesy of Warwick HRI).
(b)
bulbs are: (i) uniformity of bulb size, shape, colour and date of maturity; (ii)
high yield; (iii) appropriate maturity date; (iv) disease and pest resistance; (v)
bolting resistance; (vi) intact attractive skins; (vii) thin necks; (viii) single-
centred bulbs (freedom from double and split bulbs); and (ix) firm flesh. To
achieve many of these, the cultivar must be well adapted to the climate,
principally the day-lengths and temperatures of the season and locality in
which it is grown. In addition, bulbs for long storage need innately long
dormancy (see Chapter 7), hard flesh, tough skins and, for most markets,
pungency. Fresh bulb types should be mild-flavoured, sweet and crisp-fleshed
and, here, single centres with large, concentric rings are particularly
important. Dehydrators should have high dry-matter content, white flesh and
skin, and low reducing sugar content. Also, spherical rather than flat bulbs are
desirable for dehydrators, since this facilitates mechanical trimming of necks
and roots with little loss of bulb flesh.
Examples of the more 'cosmetic' factors that tend to be culturally con-
ditioned are the northern European preference for round, brown- or yellow-
skinned bulbs, contrasting with the Japanese preference for flatter bulbs. Such
preferences can change; for example, red onions are now popular in the UK,
whereas in the 1980s such bulbs were rarely seen there. Since preferences vary
with markets it is not possible to define fully the characteristics of an 'ideal
onion'.
Messiaen
et al
. (1993) describe the objectives of garlic selection as: (i)
smooth, round bulbs without visible defects; (ii) an even distribution of clove
size within the bulb; (iii) a low proportion of double or multiple cloves; and (iv)
