2018 ASHS Annual Conference

Botrytis cinerea causes the decaying of cut rose flowers in both production and post-harvest environments leading to economic losses. Commercial growers typically address this problem with weekly preventative fungicide applications. However, Botrytis has the ability to quickly develop resistance to single-site. This study was performed to evaluate the fungicide resistance in a commercial cut rose crop over time. Six commercial shipments of Rose ‘Orange Crush’ were received from the same greenhouse harvested over a period on several months. Upon arrival, the roses were incubated for seven days in chambers maintained at 22 ^oC and 100% humidity. When sporulation occurred after the incubation time, Botrytis conidia were collected and placed on media containing discriminatory doses of fungicides to distinguish between resistant and sensitive isolates, then incubated at 22 ^oC in the darkness for 4 d. Resistance was determined based on an observational assessment of the mycelial growth in the media for each fungicide. A total of eleven fungicides (thiophanete-methyl, iprodione, cyprodinil, boscalid, fenhexamid, penthiopyrad, fluopyram, isofetamid, fludioxonil, pydiflumetofen and polyoxin-D) belonging to seven FRAC codes were tested. A high degree of resistance was determined across the shipments to thiophanete-methyl, iprodione, cyprodinil and boscalid. In the case of fenhexamid, penthiopyrad, fluopyram, isofetamid, and fludioxonil, there was considerable variation in the fungicide resistance profiles between shipments. No resistance was detected to pydiflumetofen and polyoxin-D fungicides which was likely due to the fact that they are not yet commercially available or relatively new to the industry. A second study following the same protocols was done to evaluate resistance profiles in four commercial shipments from Rose ‘Freedom’ from five different countries including Colombia, Ecuador, Guatemala, Kenya, and Mexico. A high proportion of the isolates evaluated were consistently resistant to thiophanete-methyl and cyprodinil. Resistance profiles for the other fungicides varied with locations. Once again, no resistance was observed at any of the locations to pydiflumetofen or polyoxin-D.