Distribution of sensitivity to common botryticides in Lombardy

On grapevine, grey mould caused by Botrytis cinerea Pers. induces serious yield losses and unpleasant changes in the qualitative characteristics of berry content. Fungicides are usually applied in order to control B. cinerea but their repeated use in vineyard can select resistant strains of the pathogen. Aim of the present work is not only to monitor the sensitivity distribution of the pathogen strains to the botryticides most commonly used in vineyard, but also the possible correlation between the sensitivity level and both the mating type and the presence of transposons Boty and Flipper. During 2011, 20 strains were randomnly isolated from symptomatic samples collected in 4 vineyards selected in each of the main viticultural provinces in Lombardy, Brescia, Mantova, Pavia and Sondrio. An untreated vineyard was included in the survey. The 320 strains isolated in Lombardy were tested for their sensitivity to boscalid, fenhexamid, cyprodinil and fludioxonil, their mating type and the presence of transposons. The Resistance Factor, RF, (EC50 of the selected strain/average EC50 in the untreated vineyard) was calculated for the strains showing high EC50. RFs > 10 indicate a reduced sensitivity. The average EC50 observed in Lombardy for boscalid, fenhexamid and fludioxonil were similar to those calculated for B. cinerea in Europe, while higher values of this parameter were obtained for cyprodinil. No remarkable differences were observed in the EC50 distribution in the 4 provinces, apart from the higher values for cyprodinil and fludioxonil recorded in Pavia. RFs > 10 characterized 7, 12 and 5 strains respectively for boscalid cyprodinil and fludioxonil and 5 isolated showed a reduced multi drug sensitivity. The presence of Boty either alone or together with Flipper seems to be associated with higher RFs concerning all the tested fungicides. Association between mating type and fungicide sensitivity is less defined. From these data, B. cinerea populations in Lombardy seem to be characterized by an adequate sensitivity against botryticides. The strains showing a reduced sensitivity need to be further characterized, in particular for their fitness.