Dose-Dependent Genetic Resistance to Azole Fungicides Found in the Apple Scab Pathogen

Area of Science:

• Agricultural Science
• Plant Pathology
• Genetics

Background:

• Azole fungicides are crucial for managing fungal diseases in agriculture and human health.
• Emerging azole resistance in the apple scab pathogen, *Venturia inaequalis*, threatens crop production.
• Existing resistance mechanisms, like target site mutations, do not fully explain reduced sensitivity.

Purpose of the Study:

• To investigate the genetic basis of polygenic resistance to tebuconazole in *Venturia inaequalis*.
• To identify quantitative trait loci (QTLs) associated with fungicide resistance.
• To explore potential resistance gene candidates within identified QTL regions.

Main Methods:

• Genotyping by sequencing (GBS) was employed to map QTLs.
• Population-based analysis was used to study dose-dependent resistance.
• Genetic variation within QTL regions was examined for candidate genes.

Main Results:

• Two major QTLs significantly contributed to tebuconazole resistance.
• A QTL on linkage group seven explained 65% of variation in ED50 and influenced lower dose resistance (ED10).
• A second QTL on linkage group one explained 34% of variation at ED10 but not at higher doses.

Conclusions:

• Fungicide resistance in *Venturia inaequalis* is controlled by multiple genes with dose-dependent effects.
• ATP-Binding Cassette and Major Facilitator SuperFamily transporter genes are implicated in resistance.
• Identifying these resistance genes can aid in developing molecular diagnostics for disease management.