2018 ASHS Annual Conference

Armillaria root rot (ARR) disease is affecting stone fruit and nut crops throughout the U.S. and is the greatest threat to peach and cherry orchard sustainability in the southeastern U.S. and the Great Lakes Region, respectively. ARR has become a serious and widespread problem in the major tart and sweet cherry production regions of Michigan and is responsible for tens of millions of dollars in losses in historic peach production regions of Georgia and South Carolina. The causal soil-borne fungi, Armillaria spp., infect the root system, typically killing trees when they are reaching their maximum productivity, making orchards unprofitable, and the infected land unsuitable for continued stone fruit production. At present, there is no environmentally safe, clean management strategy for ARR in Prunus spp. tree fruits, and the few management options that are available are only marginally effective at best. The longer peach and cherry trees are cultivated at a single location, the more fungal inoculum in the form of infested root pieces builds up in the soil. Therefore, replant sites with a history of ARR are considered economically unfeasible for continued peach and cherry cultivation. At such locations, it is not uncommon for trees of only 3 and 4 years of age to succumb to ARR. Therefore, the most economical and potentially effective solution to combat Armillaria is through use of genetic resistance. To understand ARR tolerance/resistance in Prunus and uncover potential sources of tolerance/resistance that could be used in rootstock breeding, we used in vitro infection to screen 81 Prunus wild accessions from the National Clonal Germplasm Repository in Davis, CA. Preliminary results of the in vitro screen and root microscopy confirm tolerance to A. mellea in a few P. cerasifera accessions. Implications for breeding new resistant rootstocks via introgression of resistance genes from wild relatives into stone fruit-compatible rootstocks will be presented.