Agriculture Reference
In-Depth Information
Because of the widespread intercrossing and breeding of new cultivars
that is continuously occurring, there is little point in drawing up formal
classification schemes for grouping varieties. Each country or region tends to
have its traditional varieties, so any discussion of specific cultivars is inevitably
highly selective. Here, a few particular cultivars which have been important in
breeding or world trade will be discussed to illustrate some important types of
onion and to show the background to their development.
In the USA three broad classes of fresh-market onions are produced. The
southernmost states produce the autumn-sown, early, sweet cultivars, the
development of which has been discussed above. In the western mountain states
cv. 'Sweet Spanish' and similar types are sown in late winter to produce large, mild,
sweet bulbs in August and September. These types can be stored for several
months. In the north and north-east of the USA long-day cultivars are grown,
which are hard, pungent and long-keeping. Dehydrated onions are also an
important product in the USA and both the long-day cv. 'Southport White Globe'
and the short-day cv. 'White Creole' were developed to have the white skins, white
flesh and high dry matter content that are ideal for dehydration and processing to
produce onion flakes and powder (Jones and Mann, 1963). The California-bred cv.
'Southport White Globe' is grown for processing in many other parts of the world
including Spain, New Zealand and Argentina (Bosch-Serra and Currah, 2002). In
the USA hybrid cultivars are increasingly used, but open-pollinated, non-hybrid
varieties persist, particularly where transplants are grown e.g. southern Texas.
The obvious advantages of hybrids to seed companies are that they keep control of
the parent lines and varieties do not breed true from farmer-saved seed.
In north-western Europe the dominant cultivars are mainly similar to, and
developed from, the old Dutch Rijnsburger type. Their bulbs are globe-shaped,
yellow- to brown-skinned, firm, pungent and long-storing. In recent years F
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hybrids have constituted an increasing proportion of this type of onion. Of the
cultivars of spring-sown bulb onion listed by the National Institute of
Agricultural Botany (NIAB) in the UK, five out of 17 were hybrids in 1982,
whereas in 1992, 19 out of 21 were hybrids (NIAB, 1982, 1992).
Spanish onions have long been renowned as an export crop to northern
Europe. The firm-fleshed, round, long-storing 'Grano' type onions are harvested
in July and August and produce a high-quality crop. Many cultivars which have
become important in other parts of the world derive, at least in part, from this
type, including the remarkably long-storing cv. 'Pukekohe Long Keeper' of New
Zealand (Grant and Carter, 1986) and its Australian derivative, cv. 'Creamgold'.
The main types of onion suitable for growing in temperate and
Mediterranean climates were tabulated by country within each continent by
Bosch-Serra and Currah (2002). This list names particular cultivars of each
type and highlights features which are important for the markets served, e.g.
bulb shape, colour, storability, etc. These authors also include a table, based on
the work of Tarakanov, which describes similar features for cultivars grown in
Russia and territory of the former USSR.
