Study of Venturia inaequalis sensitivity to strobilurins: correlation between molecular and biological approaches

Scab caused by Venturia inaequalis (Cke.) Wint. is the most important disease of apple-tree worldwide and requires a high number of fungicide applications. The introduction, in the late 1990s, of strobilurin fungicides led to improve the disease control. After a few years of excellent protection, several cases of reduced scab control caused by pathogen resistance to strobilurins were reported in many countries. Our previous studies pointed out the occurrence in Italy of V. inaequalis populations resistant to kresoxim-methyl and trifloxystrobin, with the presence of G143A substitution in cytochrome b, which is the most common mutation in strobilurin resistance in plant pathogenic fungi. The aim of this study was to compare the sensitivity evaluation of several V. inaequalis populations coming from distinct locations obtained by conidial germination tests (DE50, percentage of germination at the higher concentration) and molecular analysis detecting presence and frequency of G143A substitution (CAPS PCR and Real Time PCR). Preliminary results from samples collected in 2009 and 2010, generally demonstrate a good but not completely clear correlation between these different approaches.