Sensitivity of Botryosphaeria dothidea from apple to tebuconazole in China

• Tebuconazole sensitivity of 146 isolates of Botryosphaeria dothidea obtained from different provinces in China was investigated.
• The isolate HB13 with the highest EC50 was tested for stability and pathogenicity compared with sensitive isolates.
• Tebuconazole cross resistance with carbendazim and iprodionefor was also checked.

The white rot disease caused by Botryosphaeria dothidea threatens apple production in Bohai bay area and along the Yellow River of China, where disease control is largely dependent on fungicides such as tebuconazole. A total of 146 isolates of B. dothidea obtained from different apple orchards in six provinces were tested for their sensitivity to tebuconazole, carbendazim and iprodione. The EC50 values of all tested isolates for tebuconazole were from 0.035 to 1.415 μg/mL. The broad range of EC50 values of tebuconazole suggests an obvious variation among the 146 isolates. Isolate HB13 (EC50 = 1.415 μg/mL) showed reduced sensitivity to tebuconazole, with an EC50 value significantly higher than those of the other 145 isolates tested. The low sensitivity of HB13 was stable after 15 generations, and this isolate showed similar pathogenicity as susceptible strains. EC50 correlation analysis indicates no cross resistance between tebuconazole and carbendazim and iprodione. Field efficacy trials showed that tebuconazole remains very effective for apple white rot control in China.