Going Back to the Source for a Heartier Apple Tree

This material shows potential for helping breed trees that bear popular, domestic apples while standing up to destructive diseases and fungi, according to Agricultural Research Service (ARS) scientists. The genetic material was gathered during U.S. Department of Agriculture (USDA) sponsored excursions to Asia and Europe aimed at expanding the known genetic diversity of apples.

Horticulturist Phil Forsline and plant geneticist Gennaro Fazio of ARS' Plant Genetics Research Unit have used the material to raise orchards of the exotic apples near their laboratory in Geneva, N.Y. And, with colleagues in ARS and Cornell University, they've documented with astonishment the disease resistance of many of these trees and the domestic species they've bred with them.

Forsline went on seven of the collecting trips, including four to central Asia. The trips resulted in at least a doubling of the known genetic diversity of apple trees, according to Forsline. The scientists returned with 949 apple tree accessions from central Asia alone. Other excursions were to China, the Caucasus region including Russia and Turkey, and Germany.

Fazio and Forsline are most impressed with the material collected in Kazakhstan, especially accessions of Malus sieversii, an important forerunner of the domestic apple. This is logical, given that Kazakhstan is a likely ancestral origin of familiar domestic apples (Malus x domestica) such as Red Delicious, Golden Delicious and McIntosh.

According to Forsline, the Kazak trees showed significant resistance to apple scab—-the most important fungal disease of apples—as well as to fire blight. They were highly resistant against Phytophthora cactorum, which causes collar rot, and Rhizoctonia solani, an agent of apple replant disease, according to Fazio. Both researchers found genes in the Kazak apples that allow them to adapt to mountainous, near-desert, and cold and dry regions.