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POSTERS: Host resistance screening

Susceptibility of geranium and snapdragon cultivars to Pythium irregulare
Nicole Lukasko - Michigan State University. Mary Hausbeck- Michigan State University, Blair Harlan- Michigan State University

The U.S. floriculture industry was valued at $4.4 billion in 2015, with Michigan as a top producer. Pythium root rot affects many economically important plants, including popular annuals such as geranium and snapdragon. Disease symptoms include stunted growth, delayed flowering, and plant death. To reduce fungicide reliance, twelve cultivars each of geranium and snapdragon were evaluated for root rot susceptibility in a greenhouse study. Seedlings were transplanted into millet infested with Pythium irregulare. Plant health and height were compared to non-inoculated (control) plants. ‘Maverick White’ and ‘Horizon White’ geraniums were the most susceptible; height of inoculated plants was reduced by 81% and 80%, respectively, and received poor health ratings. In contrast, inoculated ‘Tornado White’ geraniums were 17% smaller than the control and were rated highly for plant health. Other inoculated geranium cultivars were 37% to 77% the size of the control plants. ‘Bells White’ snapdragons were reduced in size by 47% when inoculated with P. irregulare compared to the control and had the lowest health rating. ‘Floral Showers White’ snapdragon was slightly reduced in size (3%) when inoculated compared to the control. All other inoculated snapdragon cultivars ranged in size from 63%-88% of the control plants. Choosing cultivars that are less susceptible to P. irregulare can be used in an integrated management program that also includes sanitation and other strategies.