Baseline sensitivity of Stemphylium vesicarium, the causal agent of pear brown spot, to boscalid

INTRODUCTION The control of Stemphylium vesicarium (Wallr.) Simm., the causal agent of pear brown spot, is a true concern for pear growers in Italy because many fungicide treatments are required from petal fall to fruit ripening (Ponti et al.,1996; Brunelli et al., 2004). The occurrence of resistance to dicarboximides in the early 1990’s (Brunelli et al., 1997) and to strobilurins in 2006 (Collina et al., 2007) complicated the control of this pathogen even more. The introduction in the field of new fungi-cides with different mechanisms of action is thus fundamental in order to enlarge the range of effective fungicides against pear brown spot and to reduce the risk of further resistances. At the end of the 2006 season boscalid was registered in Italy for pear. It belongs to the carboxamide-fungicide group and inhibits the respiratory chain acting on the enzyme succinate dehydrogenase in complex II (Stammler et al., 2007). This mode of action is different from that of both dicarboximide and strobilurin fungicides and it could be used in cases of field resistance to these compounds. Nevertheless, boscalid is considered by the FRAC to have a medium risk of resistance for its spe-cific target (www.frac.info). In order to evaluate the sensitivity of S. vesicarium to this fungicide, an in vitro assay was developed comparing different methods (on mycelial growth with differ-ent media and on conidial germination). Baseline sensitivity was then determined for isolates which have never been exposed to boscalid.