Abstract
Fungicide resistance is a constant threat to agricultural production worldwide. Molecular mechanisms of fungicide resistance have been studied extensively in the wheat pathogen Zymoseptoria tritici. However, less is known about the evolutionary processes driving resistance development. In vitro evolutionary studies give the opportunity to investigate this. Here, we examine the adaptation of Z. tritici to fluxapyroxad, a succinate dehydrogenase (Sdh) inhibitor. Replicate populations of Z. tritici derived from the sensitive isolate IPO323 were exposed to increasing concentrations of fluxapyroxad with or without UV mutagenesis. After ten increases in fungicide concentration, sensitivity had decreased dramatically, with replicate populations showing similar phenotypic trajectories. Sequencing the Sdh subunit B, C, and D encoding genes identified seven mutations associated with resistance to fluxapyroxad. Mutation frequency over time was measured with a pyrosequencing assay, revealing sequential lineage replacement in the UV‐mutagenized populations but not in the untreated populations. Repeating selection from set time‐points with different fungicide concentrations revealed that haplotype replacement of Sdh variants was driven by dose‐dependent selection as fungicide concentration changed, and was not mutation‐limited. These findings suggest that fungicide field applications may select for highly insensitive Sdh variants with higher resistance factors if the fungicide concentration is increased to achieve a better disease control. However, in the absence or presence of lower fungicide concentrations, the spread of these strains might be restricted if the underlying Sdh mutations carry fitness penalties.
Highlights
Populations require genetic variability to adapt to new environments or toxicants
As the succinate dehydrogenase inhibitor (SDHI) sensitive isolate Z. tritici IPO323 was used as progenitor of all populations, no external genotypes entered the mutant populations and no genetic exchange among populations occurred, so mutation was the only source of genetic variability
This haplotype was associated with a high level of insensitivity to fluxapyroxad and lower levels of insensitivity to carboxin and fluopyram (Table 1)
Summary
Populations require genetic variability to adapt to new environments or toxicants. As well as natural standing variation Laboratory studies using single generation exposures to different SDHIs have reported several target-site mutations conferring reduced sensitivity in mutants of Z. tritici and other plant pathogens (Fraaije et al, 2012; Scalliet et al, 2012; Sierotzki & Scalliet, 2013; Skinner et al, 1998). These Sdh variants display low levels of insensitivity, and control of SLB has not been affected so far This may change as field strains carrying C-H152R, showing high resistance factors to SDHIs in vitro, have recently been detected in Ireland (Dooley, Shaw, Mehenni-Ciz, Spink, & Kildea, 2016) and the UK The extent of fitness penalties associated with mutations in the target protein conferring resistance to SDHIs, and the functional constrains affecting Sdh evolution under SDHI field selection where populations are exposed to different dose rates and spray frequencies remain unknown. Studies on archived populations over time showed the mutation rate was not a limiting factor in UV- mutagenized lines and that the haplotype replacement of Sdh variants was governed by dose-d ependent selection as the “selective window” of the fungicide concentration changed
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
