Agriculture Reference
In-Depth Information
Apples at a Glance
Chilling requirements:
32 to 55°F (0 to 13°C) for 100 to 1,700 hours
from fall through late winter, depending on variety
Growing season:
Length differs according to variety: anywhere from
70 days to 180 days.
Soil pH and type:
Deep, well-drained soils with a pH between 6 and 7
Pollination:
Most varieties require cross-pollination; place a pollinizer
within 50 feet of tree.
Variety selection:
Match your site's characteristics with the variety's
chilling requirement, hardiness rating, and required growing season
length. Emphasize disease resistance.
Without becoming too technical, the odd number of chromosomes in apples
(× = 17) and the occurrence of four possible ploidy levels (the number of sets
of chromosomes) greatly complicate breeding efforts by tending to preserve
undesirable genes. Breeders call this process “enforced hybridity.” While the
genetic basis of the undesirable genes was unknown at the time, even an-
cient orchardists recognized the problem. Theophrastus noted that trees
grown from seed almost always produce inferior-quality fruit. As early as
5000
BCE
, fruit trees were being commercially grafted to preserve desirable
traits.
Despite the long history of cultivation and the existence of approximately
25 apple species, advances in apple breeding have been remarkably limited.
Although there are thousands of named apple varieties, they are derived
from a rather narrow genetic base and one that has not drawn much on
genes for pest and disease resistance. As a result, we have many beautiful,
