A Shortened Wait to Discover If Apple Tree's
a Dwarf By Luis
November 4, 2003
Service scientists may have significantly reduced the time it takes to tell
if an apple tree will grow to be a dwarf and resist diseases. Through
genemapping, plant geneticist Genarro Fazio and plant biologist H. Todd
Holleran of the ARS Plant Genetic Resources
Unit in Geneva, N.Y., have discovered the genetic inheritance of the
dwarfing characteristic in apple tree roots, also known as rootstocks.
The discovery can help researchers find molecular markers that
can help identify dwarf varieties, as well as positive and negative traits
within those varieties, early in their development. Currently, a tree must grow
for about 12 years before growers can tell whether it's a dwarf. In all, the
entire process of evaluating rootstocks for tree size and disease resistance
takes about 30 years per tree.
According to Fazio, the ability to read genetic markers may cut
these evaluation times in half. In addition, further understanding of the
workings of the genetic inheritance gene may make it possible to transfer the
knowledge to other tree fruit systems. Fazio is director of the Geneva lab's
apple rootstock breeding project.
Dwarf varieties of apple trees have become popular among growers
during the past 25 years. While normal-sized trees commonly grow to a height of
20 to30 feet, dwarf varieties grow only 10 to 12 feet tall. Their yield and
fruit size are the same as from full-sized trees, but growers can plant about
seven times as many trees per acre. Dwarfs are also easier to spray for bugs
and to prune and harvest.
In all, apples are a $1.5 billion-a-year industry. They are
grown commercially in 35 states.