Genetic basis of fungicide resistance and risk assessment for resistance Flashcards
Describe five mechanisms through which fungi can become resistant to fungicides.
Target site modification
bypass target (alternative metabolic pathway)
Detoxification
reduced uptake
Accelerated efflux
What is an ABC transporter and how is it connected to fungicide resistance?
one of the largest protein families, carry a wide variety of compounds, mainly hydrophobic, with ATP against the concentration gradient.
In fungi their functions are:
secretion of phytotoxins, mycotoxins, virulence factors and mating type factors as well as protection against plant defense compounds, natural antimicrobial compounds and fungicides
What are three risk factors that can affect the development of resistance to fungicides? Explain how each risk factor contributes to resistance.
Nature of the fungicide
modification of proteins, single mutation, prevent uptake, accelerate excretion, detoxify compound
The way the fungicide is used
driving factor is amount of selection placed on the fungal population
the more the fungicide is applied and the more widespread its use, the greater the selection placed on fungal population
The biology of the pathogen
based mainly on population genetics
rate of evolution is a function of mutation rate, population size, gene flow, mating system and selection
What strategies can be used to counteract risk factors that affect the development of resistance to fungicides?
Apply fungicide only when needed, ideally based on a disease risk predicition or forecasting model
Use fungicides as part of an integrated control program, in conjunction with genetic resistance and cultural control methods. “Dynamic diversity”
Rotate through fungicides with different modes of action during the season. “Dynamic diversity”
Use mixtures of alterations of fungicides with different modes of action. “Dynamic diversity”
Inculde multisite fungicides in mixtures or rotations with specific-site fungicides. “Dynamic diversity”
How can you differentiate between fungicide resistance due to the action of several mutations and resistance due to a single mutation?
Single mutation is sufficient to create resistance, the resistance is absolute
several mutations: two mutations (or more) are necessary to display a resistance similar in strength, two genes act together
How does monogenic inheritance of fungicide resistance differ form polygenic inheritance?
Monogenic:
When the fungicide was introduced first, populations showed a relatively normal distribution of resistance, ten years after starting to apply fungicide, the distribution of resistance in the population was bimodal, half of isolates still susceptible and abou half needing abou 30x more chemical to achieve control
polygenic:
if fungicide resistance is conditioned by several independent genes showing equal adn additive effects, the susceptibility of population was distributed continuosly
Monogenic resistance develops into a sharp distinction between susceptible and resistant individuals.
Polygenic resistance in exposed populations increases the mean resistance score of individuals.
What is negative cross-resistance? Give an example of negative cross-resistance.
Resistance to one chemical leads to suscepotibility to another chemical
Botrytis cinerea became resistant to benzimidazol (MBC). Mutation in the gene encoding B-tubulin. Fortunately the strains that were resistant to MBC fungicides were eben more susceptible to antoher fungicide called diethofencarb, which also targets B-tubulin
What is multidrug resistance and how does it differ from typical fungicide resistance?
resistance to several chemicals (?)
Explain how multidrug resistance emerged in European populations of Botrytis cinerea.
In Europe, Botrytis cinerea became resistant to MBC after these chemicals became widely used in vineyards. Due to negative cross-resistance, the populations became susceptible to diethofencarb. Multiple mutations in the target gene and continuous use of the fungicides in mixtures led to the development of resistance to both compounds. Grape growers switched to a different fungicide class (anilinopyrimidines, ergosterol biosynthesis inhibitors).
How does FRAC assess the risk that fungi will evolve resistance to fungicides?
taking into account the mode of action of the fungicide and the biology of the pathogens
Basic disease risk: generation time, amount of sporulation, potential fot gene flow
basic fungicide risk: fungicide class, site of action, cross-resistance, pathogen response to mutagens, pathogen response to sequence of fungicide applications
Based on interactions among these factors, FRAC developed a risk assessment scale ranging from 1-9
