Diversity and fitness of <Emphasis Type="Italic">Plasmopara viticola</Emphasis> isolates resistant to QoI fungicides |
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Authors: | Marie-France Corio-Costet Marie-Cécile Dufour Jérémy Cigna Pierre Abadie Wei-Jen Chen |
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Institution: | 1.UMR Santé Végétale, 1065, ISVV, IFR 103,INRA,Villenave d’Ornon,France;2.UMR 1202 BIOGeCo, Laboratoire de génétique des arbres forestiers,INRA,Cestas,France;3.Institute of Oceanography,National Taiwan University,Taipei,Taiwan |
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Abstract: | The effectiveness of Quinone outside Inhibitor (QoI) fungicides against grape downy mildew in European vineyards has significantly
decreased in the last decade. One nucleotide polymorphism, G143A in the cytochrome b gene of Plasmopara viticola, is involved in resistance to QoIs. Previous genetic examination on the mitochondrial genomes showed four major haplotypes
(IR, IS, IIR, IIS) coexisting in European vineyards. A resistant allele (G143A) was present in IR and IIR haplotypes. The
purpose of the present study was to estimate the diversity of the different mitochondrial haplotypes and their distribution
in QoI-resistant populations before evaluating the potential cost of the resistant mutation G143A in P. viticola population. From 2000 to 2004, the frequencies of resistant isolates ranged from 0% to 23.25% with an average of 4.64 % among
the populations examined. To evaluate the fitness of sensitive and resistant isolates, a comparison of different biological
parameters including latent period, spore production and infection frequency was performed, enabling a fitness index (FI) to be determined. Resistant isolates exhibited greater infection frequency than sensitive isolates, whereas no significant
difference was found in sporulation ability and latent period between sensitive and resistant isolates. To further investigate
competitiveness among isolates, an assay including two resistant isolates in different proportion with a sensitive isolate
was conducted on eight asexual growing cycles in the absence of a QoI fungicide. The competitiveness of resistant isolates
varied according to their fitness parameters, suggesting that there is no noticeable cost of QoI resistance in controlled
conditions in Plasmopara viticola. |
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