A QUALITATIVE ASSAY FOR IN VITRO DETECTION FOR POTENTIAL PROPICONAZOLE FIELD RESISTANCE IN ISOLATES OF THE DOLLAR SPOT FUNGUS, SCLEROTINIA HOMOEOCARPA

摘要

The objective of this study was to develop an in vitro assay for qualitative detection of Sclerotinia homoeocarpa isolates with potential to cause practical field resistance to DMI fungicides.Isolates from four S.homoeocarpa populations in New England were previously determined to be field resistant to the DMI fungicide propiconazole and along with isolates from a baseline population were used for this study.These isolates were collected from propiconazole-treated (0.44 kg a.i.ha-1) and untreated plots at two time points at each site: (i) initial (before application) and (ii) 7-days after treatment (7- DAT).Isolates sampled 7-DAT were considered to exhibit practical field resistance since they were collected from dollar spot infection centers during the control period of propiconazole (which is labeled for a minimum of 14 day residual control).Isolates were assayed to calculate relative mycelial growth percentages (RMG%) on agar medium amended with increasing concentrations of propiconazole to determine if the growth of isolates capable of causing practical field resistance could be qualitatively differentiated from sensitive isolates.Practical field resistant isolates were sampled 7-DAT from the four resistant sites,but not the baseline site,and mycelial growth of all baseline isolates was completely inhibited by 1.0 μg a.i.ml-1 of propiconazole.However,nearly all field resistant isolates (98.7%) obtained from propiconazole treated plots 7-DAT at the HGC,HRCC,SMCC and WBGC exhibited mycelial growth at 1.0 μg a.i.ml-1 of propiconazole.These results suggest that the concentration 1.0 μg a.i.ml-1 of propiconazole can be suitable for qualitative in vitro assessment of S.homoeocarpa isolates that may cause practical field resistance to DMI fungicides.