Abstract
Multisite fungicides have been used for many years in fruit and vegetable crops worldwide. Cases of the fungi resistance development to these fungicides have been rare. From the 2002 season onwards, with the outbreak of Asian soybean rust in Brazil, caused by Phakopsora pachyrhizi, site-specific fungicides became the main weapon for its control. From 2002 to 2011, penetrant mobile site-specific fungicides were used and until today in double (DMI + QoI) or triple (DMI + QoI + SDHI) co-formulatoons in an area of more than 30 million hectares and with three sprays per area. This resulted, as expected, in the fungus sensitivity reduction, today with cross and multiple resistance to those site-specific fungicides. From the 2011 season in an attempt to recover control that for some chemicals and mixtures reached < 30%, research was started with site-specific + multi-site mixtures, taking as example Phytophthora infestans resistance development to metalaxyl in Europe showinig long-lasting solution found by the addition of multisite mancozeb. It is expected that the effective life of site-specific + multi-site mixtures may be as long in controlling soybean rust as it has been for potato, tomato and grape downy mildews. This review presents the concepts involved in the sensitivity reduction to fungicides. Some fungal species and fungicides involved are listed. Considering the P. pachyrhizi sporulation potential, the great soybean area sprayed and the number of sprays per area mainly with site-specific co-formulations and the reduced area sprayed with multisites, we discuss the need for annual monitoring of P. pachyrhizi sensitivity to the these chemicals.
Highlights
Between 1940 and 1970, fungicidal organic compounds with a broad spectrum of activity were developed by the plant protection chemical industry
It was soon found that plant pathogenic fungi can and quickly adapt to these fungicides through mutations that lead to reduced efficacy (Klittich, 2008; Mosbach et al, 2017)
Reducing sensitivity to fungicides involves a fundamental property of fungi, the ability to adapt to different environmental conditions, usually adverse, and to survive
Summary
Between 1940 and 1970, fungicidal organic compounds with a broad spectrum of activity were developed by the plant protection chemical industry. It was soon found that plant pathogenic fungi can and quickly adapt to these fungicides through mutations (among other resistance mechanisms) that lead to reduced efficacy (Klittich, 2008; Mosbach et al, 2017). Reducing sensitivity to fungicides involves a fundamental property of fungi, the ability to adapt to different environmental conditions, usually adverse, and to survive. Frequent use of fungicides creates an adverse environment for a fungus that was previously sensitive to a particular compound, leading to its adaptation and resistance to the new situation (Bardas et al, 2008; Kretschmer, et al, 2009). From the 1970s, the resistance of phytopathogenic fungi became a problem with the predominant use of mobile-penetrating fungicides that were site-specific (Klittich, 2008). With the introduction and repeated use of site-specific, acquired resistance has become common but incomparable to multisite (van den Boch & Gilligan, 2008)
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