2017 ASHS Annual Conference

Botrytis cinerea can infect approximately 200 species of plants, many important to the floriculture industry. During shipping and storage, unrooted cuttings are subject to high relative humidity, which is conducive for disease development, and drastic swings in temperature. Unrooted cuttings of four cultivars of Pelargonium × hortorum L.H. Bailey, ‘Americana Red’ (AR), ‘Patriot Bright Red’ (PBR), ‘Patriot Rose Pink’ (PRP), and ‘Tango Dark Red’ (TDR), were received from commercial suppliers and were either left untreated, or treated with 1.0 uL∙L of ethylene (ET) or 700 nL∙L of 1-methylcyclopropene (1-MCP). After 22 hours of incubation, cuttings from each treatment were either left dry or sprayed with a spore suspension of 2 x 10^6 spores per mL. After incubating for four days, in high humidity chambers, cuttings were rated for disease severity (BR). All cultivars increased in ET production over the four-day incubation. ‘Tango Dark Red’ (TDR), ‘Patriot Bright Red’ (PRP), ‘Patriot Bright Red’ (PBR), and ‘Americana Red’ (AR) produced an average of 1.12, 0.88, 0.62, 0.60 uL∙L of ET, respectively. However, depending on a treatment of ET or 1-MCP and whether inoculated or not, cultivars produced differing levels of ET. 1-MCP significantly increased ET production for most cultivars. Treating with ET had a weaker effect, but still increased ET production in some cultivars. 1-MCP did reduce or keep leaf yellowing at similar levels to the control, while ET significantly increased leaf yellowing in most cultivars. PRP was significantly the most susceptible to botrytis while AR and TDR often switched between ranking as the least susceptible. Treatments of 1-MCP or ET sometimes caused TDR to have as much disease as PBR. 1-MCP did significantly reduce botrytis ratings (BR) for all cultivars except the least susceptible AR when compared to controls. Treating cuttings with ET significantly increased BR in some cultivars. Cultivars of geranium do show varying levels of susceptibility to botrytis and act differently in correspondence to ET or 1-MCP. These gases do have a small effect on botrytis severity. However, correlations between cultivars’ susceptibility to botrytis and pretreatments of either ET anti-ethylene, 1-MCP, are not consistent leading us to believe that a cultivars’ sensitivity to ET may play a small role in disease severity.