Persistence of <i>Venturia inaequalis</i> Populations Resistant to Strobilurins in the Field and in the Glasshouse

Abstract

The research was focused on the persistence of resistance of V. inaequalis to strobilurins from resistant populations occurring in the field. It was studied with two types of experiments: the first in apple orchards where resistance occurred in 2005 and employ of these fungicides was suspended from 2006 to 2011, realizing every year sensitivity/resistance assays on strobilurins. In the second was verified the sensitivity/resistance of the same 2015 populations, repeatedly multiplied (ten inoculations) in glasshouse on apple seedlings. Results showed that the resistance survived in orchards all the years of tests (six years), despite sensitivity fluctuations occurred on infected leaves due to sexual crosses, competition with sensible strains and soil management. In glasshouse, the level of resistance of all populations increased quickly in first inoculations and values remained high (EC 50 > 10 mg·L -1 ) in all the following inoculations, until the last, the 10th. V. inaequalis resistant strains seemed to show high fitness: relevant persistence in the field, and a capacity of prevail on sensible ones in absence of factors of field variability.