2019 ASHS Annual Conference

Throughout the U.S., stone fruit and nut crops (peach in South Carolina, Georgia, and California; cherry in Michigan; almond in California) are under threat from Armillaria root rot (ARR), for which there are no long-term control or mitigation strategies. ARR is the main factor in mature orchard decline, and the causal fungi are comprised of multiple Armillaria species, which infect and reside in the root system and kill trees long before they reach their maximum productivity. There is one commercially available rootstock with resistance to ARR for peach (MP29), but it is not widely accepted by growers. Furthermore, ARR resistant rootstock development is hampered by the difficulties associated with inconsistent infection, time and other complexities in the greenhouse and field hotspots, respectively. To make advancements toward our understanding of resistance mechanisms expressed in the MP29 rootstock, we developed an even population of MP29 clonal propagates and a population of Prunus persica susceptible controls (GF305) and co-cultivated them with Armillaria mellea for a period of 12 weeks. We observed rapid canopy decline after 3 weeks in the inoculated GF305 genotype; while MP29 showed no signs of decline. Furthermore, the GF305 inoculated lines were completely dead at 8 weeks, while MP29 persisted well beyond 12 weeks, suggesting validation of resistance to heavy pathogen pressure in the in vitro system. To develop an understanding of the genetic mechanisms endowing resistance to ARR, we sequenced complete transcriptomes of both the GF305 and MP29 genotypes under inoculated and non-inoculated conditions. The in vitro co-culture system and gene expression analysis will be presented.