Related Experiment Video
Updated: Jun 28, 2026
A Contrast of Three Inoculation Techniques used to Determine the Race of Unknown Fusarium oxysporum f.sp. niveum Isolates
Published on: October 28, 2021
Multiple Loci Determining Insensitivity to Phenylamide Fungicides in Phytophthora infestans
Abstract:
ABSTRACT The diversity of mechanisms causing insensitivity to phenylamide fungicides in Phytophthora infestans was addressed by comparative genetic analyses of isolates from North America, Europe, and Mexico. Both semidominant major loci (MEX loci) and genes of minor effect were previously shown to determine insensitivity based on studies of isolates from Europe and Mexico. In this investigation, genetic analyses of three highly insensitive isolates from the United States and Canada revealed a similar pattern involving major and minor loci. However, MEX alleles in two Canadian isolates conferred higher levels of insensitivity than those examined previously, particularly in a heterozygous state. This suggested that not all MEX alleles in P. infestans were functionally equivalent. The chromosomal locations of the major insensitivity loci were also shown to vary in different isolates based on linkage analyses performed with the aid of DNA markers. The major determinant of insensitivity in the North American, Dutch, and Mexican isolates mapped to the same locus, which was named MEX1. In a British isolate, a different locus, dubbed MEX2, was implicated that mapped to the same linkage group as MEX1 but to a distinct site.
Insights
Genetic analysis reveals varying mechanisms of phenylamide fungicide insensitivity in Phytophthora infestans. Different alleles and chromosomal locations of major insensitivity loci (MEX loci) contribute to resistance in various geographic isolates.
Area of Science:
- Plant Pathology
- Fungal Genetics
- Agricultural Science
Background:
- Phenylamide fungicides are crucial for managing potato late blight caused by Phytophthora infestans.
- Insensitivity to phenylamide fungicides in Phytophthora infestans is a growing concern for crop protection.
- Previous studies identified semidominant major loci (MEX loci) and minor genes contributing to fungicide insensitivity.
Purpose of the Study:
- To investigate the diversity of genetic mechanisms underlying phenylamide fungicide insensitivity in Phytophthora infestans.
- To compare genetic factors of insensitivity across isolates from North America, Europe, and Mexico.
- To characterize novel alleles and chromosomal locations of major insensitivity loci.
Main Methods:
- Comparative genetic analyses of Phytophthora infestans isolates.
- Linkage analyses using DNA markers.
- Evaluation of insensitivity levels in different genetic states (e.g., heterozygous).
Main Results:
- A similar pattern of major and minor loci determining insensitivity was observed in North American isolates.
- Certain MEX alleles conferred higher insensitivity, especially in the heterozygous state, indicating functional nonequivalence.
- Major insensitivity loci (MEX1 and MEX2) were mapped to different chromosomal locations across various geographic isolates.
Conclusions:
- The genetic basis of phenylamide fungicide insensitivity in Phytophthora infestans is diverse, involving both major and minor genetic factors.
- Allelic variation at MEX loci contributes to differing levels of insensitivity.
- Chromosomal location of major insensitivity loci can vary, impacting fungicide resistance evolution.
