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POSTERS: Host resistance screening

Phlox species have varied susceptibility to powdery mildew isolates from the Eastern United States
Coralie Farinas - The Ohio State University. Pablo Jourdan- Ohio State University, Francesca Peduto Hand- The Ohio State University, Margery Daughtrey- Cornell University, Pierce Paul- The Ohio State University

Growers, landscapers, and homeowners alike face challenges growing the native ornamental plant Phlox because of its susceptibility to powdery mildew (PM) caused by the fungi Golovinomyces magnicellulatus and Podosphaera sp. To fight off the disease, many economically and environmentally expensive fungicides are frequently used. In this study, we collected 15 powdery mildew isolates throughout the Eastern U.S. and used them to carry out resistance screening of perennial Phlox germplasm using a recently developed in vitro assay. Separate groups of micropropagated plantlets of P. paniculata, P. amoena, P. subulata, and P. glaberrima were inoculated with 18-day-old colonies of each PM isolate. Disease incidence and severity were assessed every four days for a month, and spore production was quantified one month after inoculation. Additionally, we used a Multilocus Sequence Typing analysis to assess the genetic diversity of our PM isolates. Primers targeting five housekeeping genes (tef-1a, csI, ITS, H3, tub2) were designed from Whole Genome Sequencing of G. magnicellulatus strain FPH2017.1. To date, phylogenetic analysis by the Maximum Likelihood method using the H3 and ITS loci showed a certain degree of genetic diversity in the collected isolates. Moreover, we found that the tested Phlox species varied in susceptibility to PM isolates. Phlox paniculata ‘Dunbar Creek’ showed resistance across isolates, which is consistent with its observed performance in the landscape.