Agriculture Reference
In-Depth Information
PROPAGATION
Probably most fruits sold and consumed a few centuries ago would have
been rated as poor in quality by present standards. Fruit size, colour, fl avour,
appearance and postharvest handling have dramatically improved, while the
levels of defects, disease and pest damage have declined, especially in the last
half-century. Commercial production a few centuries ago, when most people
lived in rural areas, was based upon backyard or small orchard production,
frequently of plant material that had received limited selection. Initially, the
seed from a selection of the best type was planted, which frequently did not
ensure the maintenance of the desired selected characters, though it is an
easy approach. Large orchards cannot rely on highly variable plant material if
they want high yield and consistent fruit quality. Higher quality was achieved
by selecting superior wild trees or chance seedlings, and these genotypes were
propagated, often as vegetative materials. The use of vegetative material meant
that the genetic characteristics of these desired plants were retained and led
to the creation of varieties or cultivars. At the same time, especially in the
temperate zones, growers, nurserymen and hobbyists were fi nding new types
of plants that arose either as chance seedlings or as mutations, which they
selected and evaluated. Later, fruit-growing specialists and entire institutions
started breeding programmes that initially consisted of sowing numerous
seeds to see if some of the seedlings were better than their parents. In many
cases, nurseries or growers found mutants that were superior or had a special
characteristic. Superior plants known to exist elsewhere were asexually
propagated. Examples include the 'Fuerte' avocado, which was brought to
California as scions from Mexico; the 'Washington' navel orange, discovered
as a mutation in Brazil and its buds taken to the USA, where it was popularized
and later spread all over the world; the 'Smooth Cayenne' pineapple, discovered
in South America and taken to Hawaii; and the 'Solo' type of papaya,
discovered in Barbados and also taken to Hawaii. Many tropical fruit breeding
programmes that use modern techniques, such as mutation induction and
hybridization, to obtain superior varieties exist around the world.
Propagation of new selected cultivars is more sophisticated and relies
mainly on asexually propagating certifi ed varieties. The pineapple canning
industry relies especially on selection out of the 'Smooth Cayenne' variety,
while the pineapple fresh fruit export industry is dominated by the 'Smooth
Cayenne' low-acid hybrids. Five or six major mango varieties are the backbone
of the export trade, and the avocado varieties in international trade are 'Hass'
and 'Fuerte'. The international trade in bananas is based on one variety,
'Grand Nain', in the Cavendish group.
Many fruit trees need a rootstock that is adapted to adverse soil conditions
and has resistance to certain diseases, nematodes and insects. The rootstock
can also be required to attain a certain plant vigour, to achieve this the variety
