Phytophthora Management in Walnuts
Phytophthora crown and root rot is a serious cause of tree loss for most tree crops, including walnuts.Greg Brown is a research Plant pathologist with USDA ARS based at UC Davis
“For quite a few years we've been part of a team that's working on development of new Walnut rootstocks for resistance to soil born pathogens and my lab’s part is the resistance to Phytophthora in walnut rootstocks,” Explained Browne
Browne noted that there's been some good progress over the last decade. “In particular we've found that Juglans microcarpa is a valuable source of resistance to Phytophthora and some other pathogens too,” he said. “With the Phytophthora, we've found hybrids of Juglans microcarpa with Juglans regia, so it's different than our usual paradox hybrid rootstock. The microcarpa is different because Juglans hindsii is the usual maternal parent for Paradox rootstock.”
“The microcarpa hybrid is highly resistant to Phythopthora cinnamomi, at least the many clones that we've tested so far,” Browne said. “And so we've field-validated that resistance to Phythopthora cinnamomi in walnut, and that rootstock called RX1 is actually available in the trade now.”