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BUGS FUZZ

Focus on disease and insects

Resistance Is Futile… Or Is It? TREKKIES

SHOULD

RECOGNIZE

the first three words of the title above, attributing them to the Borg as they assimilate populations and worlds they come across. To a plant pathologist, such as I they are words used to taunt our enemy, the plant pathogens, as we test new fungicide products against them in our fight to produce and grow beautiful plants. Yet ever so often, we come across reports that there are some fungicide treatments that “used to work” but do NOT seem to work anymore! What happened? Could it be, the fungal pathogen is resisting? FUNGICIDE RESISTANCE

Fungicide resistance is defined as an acquired heritable trait that imparts a reduction in sensitivity to an antifungal agent (aka fungicide). In a chapter of a book series published in 2015 titled “The Evolution of Fungicide Resistance,” John Lucas and his co-authors noted that fungicide resistance was rare prior to the 1970s. They also noted that the 1970s were when “novel classes of antifungal chemicals with specific modes of action were introduced and became widely used”. What is the link between modes of action and fungicide resistance?  Mode of Action (MOA) explains how a particular antifungal product acts or functions to kill or stop fungal growth.

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TNLA Green March/April 2019

By Kevin Ong, Ph.D. & Erfan Vafaie

CONTROL

CONTROL

HERITAGE

DECREE

PAGAENT

COMPASS

A classical approach to determining fungicide resistance by challenging the fungus (Botrytis) to grow and sporulate on fungicide-amended potato dextrose agar (PDA) plates. Two isolates of Botrytis cinerea showing different profiles against some common fungicides.

This usually refers to one or more specific cellular processes in the fungus that are disrupted by that fungicide. The Fungicide Resistance Action Committee (FRAC) is a technical specialist group with the purpose of providing guidelines to help prolong the usefulness of the current available fungicides. FRAC categorizes the fungicides by their biochemical mode of action in the metabolic pathway of the fungal plant pathogen i.e., which part or stage of the fungal cell growth is targeted.

A more recognizable product of FRAC is the FRAC Code, often seen as Group Code on fungicide labels. These numbers (and sometimes letters) identify fungicide groups by their cross-resistance behavior. Essentially, if different fungicides have the same number, then it is likely they target the similar protein or biochemical step in the fungal pathogen. Hence the common guidance to rotate fungicide used by making sure not to use products with the same group number too many times successively. (See table1.)

Table 1. Some examples of FRAC categorization by Mode of Actions (cellular processes target) and the FRAC Code of fungicides that acts upon one or more targets noted in the MOA. MODE OF ACTION FRAC CODE Cytoskeleton and motor protein . . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 10, 20, 22, 43, 47, 50 Respiration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7, 11, 21, 29, 30, 38, 45 Amino acid and protein sysnthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9, 23, 24, 25, 41 Signal transduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. 12. 13 Lipid synthesis/membrane integrity  . . . . . . . . . . . . . . . . . . . . . . . 6, 14, 28, 44, 46, 48, 49 Sterol biosynthesis  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3, 5, 17, 18 Plant host defense induction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P01, P02 … P07 Multi-site activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M#

Profile for TNLA GREEN Magazine

TNLA Green March/April 2019  

TNLA Green March/April 2019