Sensitivityof<italic>Colletotrichumhigginsianum</italic>isolatedfrom<italic>Brassicaparachinensis</italic>toprochlorazinGuangdongProvincefrom2009to2014

In order to evaluate the varieties and changes of the sensitivity of Colletotrichum higginsianum isolated from Brassica parachinensis to prochloraz in Guangdong Province, 105 isolates of C. higginsianum were collected from 15 counties/cities of Guangdong Province from 2009 to 2014. Their EC₅₀ values to prochloraz were determined by the mycelium growth rate method in vitro. The sensitivity of the isolates from different regions to prochloraz in the same year and the sensitivity changes of the isolates to prochloraz in different years were compared. In terms of isolates collected in the same year, the minimal sensitivity difference to prochloraz among the isolates was observed in 2009. The average EC₅₀ value of the isolates with the lowest sensitivity to prochloraz was 1.2 times higher than that of the highest sensitivity. While the greatest sensitivity difference was detected in 2014. The average EC₅₀ value of the isolates with the lowest sensitivity to prochloraz was 34.9 times higher than that of the highest sensitivity. In all the other years, the ratio between the highest average EC₅₀ value and the lowest average EC₅₀ value in different regions was 9.2 to 10.4 times. With regard to isolates collected in different years, the isolates of C. higginsianum collected in 2010 showed the highest sensitivity to prochloraz, with the average EC₅₀ value of 0.052 0 μg/mL. And the isolates collected in 2012 showed the lowest sensitivity to prochloraz, with the average EC₅₀ value of 0.259 9 μg/mL. The average EC₅₀ values of isolates collected from 2012 to 2014 ranged from 0.104 5 to 0.259 9 μg/mL, which were higher than those detected from 2009 to 2011 ranging from 0.052 0 to 0.074 3 μg/mL. From 2009 to 2014, the sensitivity of isolates of C. higginsianum in Guangdong Province showed a decreasing trend to prochloraz, which indicated potential resistance risk of C. higginsianum to prochloraz.