![]() In addition, the new high-density plantings have made these diseases much more expensive in their impact. Replacing orchards means replanting on previously used sites, so replant disease is more of a problem now than it used to be. Most of the modern, new high-quality varieties are more susceptible to fireblight than is Red Delicious, a variety they are replacing. Since the breeding work began, the problems of fireblight and replant disease have gotten worse, not better. That focus apparently also gave a significant level of resistance to replant disease, of which Phytopthora can be one element. Gennaro Fazio.Īlso part of the breeding program was a focus on Phytopthora, which causes root and crown rot. Terence Robinson, and USDA plant geneticist Dr. The rootstock breeding program includes teams led by plant pathologist Aldwinckle, horticulturist Dr. Now, work at Cornell is looking at ways to make G.41 easier to propagate in the nurseries. “The goal was to make rootstocks that would help growers, and they didn’t want suckers and burr knots,” he said. It turns out, he said, that the characteristics that discourage burr knots and suckers also make those rootstocks harder to propagate. ![]() But the breeders also wanted to avoid other problems-like excessive sucker production and burr knots. It was, he said, the first rootstock breeding program to focus on fireblight resistance as a top priority. “Supplies of G.41 are still not adequate to meet demand, and it will be a couple more years before they are.”Īldwinckle was one of the original researchers who began working on rootstock breeding at Cornell 40 years ago. “We’re making a considerable effort to get supplies pumped up,” Aldwinckle said. Right now, G.41 is in short supply because nurseries have trouble propagating it in stoolbeds. “The only guaranteed method of fireblight control is the use of resistant rootstocks,” he said. Budagovsky 9, as a rootstock, is also resistant to fireblight, but it is not as good horticulturally as G.41 or M.9, Dr. G.41, which is resistant to both diseases and the size of the medium-sized clones of M.9, could be the solution across the apple-production regions of North America, perhaps the world. ![]() Fireblight is an especially severe threat in the Midwest, Northeast, and Mid-Atlantic areas, and replant disease is a major headache in the Pacific Northwest. Malling 9 dwarfs trees to the size that growers want, but the rootstock is susceptible to fireblight infection and to replant disease. Within the next two years, Cornell University plant pathologist Herb Aldwinckle hopes scientists and the tree fruit nurseries will have solved the problems of propagating Cornell’s Geneva 41 rootstock-because, he thinks, that rootstock, and maybe others, is the answer to the problems of Malling 9. ![]()
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