TITLE:
Researches on Methodologies to Verify Reduced Sensitivities of Venturia inaequalis in Field to Difenoconazole and First Indications of a Survey in Italy
AUTHORS:
Riccardo Fiaccadori
KEYWORDS:
Venturia inaequalis, Resistance, IBS, Difenoconazole, Apple-Scab Control
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.8 No.9,
August
4,
2017
ABSTRACT: Resistance
of Venturia inaequalis to the first IBS triazoles occurred in the 80’s in
Italy and other countries. Successively number of applications sensibly decreased
and problems of resistance to IBS generally disappeared. In 2010 suspects of
resistance to the newer IBS difenoconazole, the actually most used IBS,
appeared in several countries. In vitro tests the results
confirmed the previous researches: the monoconidia from populations which were
poorly controlled showed moderate reduced sensitivity respect to well
controlled and wild-types. New in vivo tests were realized with
preventive and curative applications on seedlings. No different activity among
the three types of populations (poorly, well-controlled and wild-types) was found in preventive applications. On the contrary,
in curative applications, wild-types and well controlled populations showed a
visible and statistically significant activity respect to the poorly controlled.
A survey of sensitivity to difenoconazole was carried out in two Italian apple
areas in 2013-2015 and showed the presence of populations resistant to
difenoconazole. Probably the cause of the resistance spread was the increase of
the number of applications of this IBS in the last years. However the problem
appears more complex because nowadays resistance regards about all fungicides
and with a higher severity respect previous decades. An increase of virulence
of V. inaequalis strains appears to be
the cause of this situation also for the high presence of cultivars with high
or moderate susceptibility to scab. Foreseeable remedies consist in a
differentiate and appropriate setting of each chemical groups of fungicides in
apple scab control, but in long terms new strategies in apple cultivation
should be necessary.