Molecular characterisation and detection of resistance to succinate dehydrogenase inhibitor fungicides in Botryotinia fuckeliana (Botrytis cinerea).
BACKGROUND
Succinate dehydrogenase inhibitors (SDHIs), interfering with fungal respiration, are considered to be fungicides at medium to high risk of resistance. Boscalid was the first molecule belonging to the SDHIs that was introduced for the control of Botryotinia fuckeliana. A range of different target-site mutations leading to boscalid resistance have been found in field populations of the fungus. The different types of mutation confer different cross-resistance profiles towards novel SDHIs, such as the recently introduced fungicide fluopyram. This study combines the determination of cross-resistance profiles and the setting-up of methods for fast molecular detection of the mutations.


RESULTS
By means of in vitro tests, a range of SdhB mutations were characterised for resistance levels towards boscalid and fluopyram. SdhB mutations conferring P225L and P225F substitutions conferred high resistance to boscalid and high or moderate resistance to fluopyram respectively. Mutants carrying the N230I replacement were moderately resistant to both SDHIs. Substitutions at position H272 responsible for a high level of resistance to boscalid conferred sensitivity (H272R), hypersensitivity (H272Y) or moderate resistance (H272V) to fluopyram. Allele-specific (AS) PCR was developed and used for genotyping 135 B. fuckeliana isolates. The assay confirmed the strict association between resistance profiles and allelic variants of the SdhB gene. Real-time AS-PCR proved to be sensitive and specific for quantitative detection of different SDHI-resistant genotypes.


CONCLUSIONS
Fluopyram-resistant mutants are currently rarely detected in the field sprayed with boscalid, but this may change with intensive exposure of the fungal population to fluopyram. PCR assays/methods developed in the study provide tools for fast monitoring of field populations and observing possible changes in population composition following fluopyram introduction, useful for the setting-up of appropriate preventive measures.
Plant Pathology Section, Department of Soil, Plant and Food Sciences, University of Bari, Bari, Italy.
Rita M
RM
De Miccolis Angelini
Mario
M
Masiello
Caterina
C
Rotolo
Stefania
S
Pollastro
Francesco
F
Faretra
D000595:Amino Acid Sequence; D001483:Base Sequence; D001549:Benzamides / Q000494:pharmacology; D001713:Biphenyl Compounds / Q000494:pharmacology; D020171:Botrytis / Q000187:drug effects* / Q000235:genetics / Q000502:physiology*; D025141:Drug Resistance, Fungal / Q000235:genetics*; D005659:Fungicides, Industrial / Q000494:pharmacology*; D007558:Italy; D008969:Molecular Sequence Data; D009536:Niacinamide / Q000031:analogs & derivatives / Q000494:pharmacology; D010935:Plant Diseases / Q000382:microbiology; D011725:Pyridines / Q000494:pharmacology; D060888:Real-Time Polymerase Chain Reaction; D013385:Succinate Dehydrogenase / Q000037:antagonists & inhibitors
D001549:Benzamides; D001713:Biphenyl Compounds; D005659:Fungicides, Industrial; D011725:Pyridines; D009536:Niacinamide; C550088:2-chloro-N-(4-chlorobiphenyl-2-yl)nicotinamide; D013385:Succinate Dehydrogenase; C572868:N-(2-(3-chloro-5-(trifluoromethyl)-2-pyridyl)ethyl)-alpha,alpha,alpha-trifluoro-o-toluamide
allele-specific PCR; boscalid; fluopyram; fungicide cross-resistance; grey mould; succinate dehydrogenase