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A Shortened Wait to Discover If Apple Tree's a Dwarf

By Luis Pons
November 4, 2003

Agricultural Research 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.

You can read more about this research in the November issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's primary scientific research agency.