Molecular variability of sunflower downy mildew,Plasmopara halstedii, from different continents

Abstract

Downy mildew of sunflower (Helianthus annuus L.), caused by the pathogen Plasmopara halstedii, is a potentially devastating disease. Seventy-seven isolates of P. halstedii collected in twelve countries from four continents were investigated for RAPD polymorphism with 21 primers. The study led to a binary matrix, which was subjected to various complementary analyses. This is the first report on the international genetic diversity of the pathogen. Similarity indices ranged from 89% to 100%. Neither a consensus unweighted pair group method with arithmetic means (UPGMA) tree constructed after bootstrap resampling of markers nor a principal component analysis based on distance matrix revealed very consistent clusterings of the isolates, and groups did not fit race or geographical origins. Phylogenies were probably obscured by limited diversity. Analysis of molecular variance (AMOVA) and Nei's genetic diversity statistics gave similar conclusions. Most of the genetic diversity was attributable to individual differences. The most differentiated races also had the lowest within-diversity indices, which suggest that they appeared recently with strong bottleneck effects. Our analyses suggest that this pathogen is probably homothallic or has an asexual mode of reproduction and that gene flow among countries can occur through commercial exchanges. Knowledge of the downy mildew populations' structure at the international level will help to devise strategies for controlling this potentially devastating disease.

Biochemical and Molecular Changes in Downy Mildew‐infected Sunflower Triggered by Resistance Inducers

“…Although downy mildew of sunflower (Plasmopara halstedii) can be effectively controlled by using resistant cultivars and⁄or by applying fungicides as seed treatment, protection can be hindered by the genetic variability of the fungus (Albourie et al 1998;Roeckel-Drevet et al 2003;Gulya 2007). Thus, there is a need for research into alternative methods of effective disease control.…”

Development of sunflower genotypes resistant to downy mildew

“…These two genes controlled the downy population in Europe until 1998 when new races emerged (710 and 703) in France (Tourvieille de Labrouhe et al, 1991). Later research showed that these races were introduced from the USA via infected seeds (Roeckel-Drevet et al, 2003). After the introduction of these races, there occurred a conflagration of new downy mildew races, especially in France.…”

Methodology of virulence screening and race characterization of Plasmopara halstedii, and resistance evaluation in sunflower – a review

“…Random amplified polymorphic DNA (RAPD) PCR markers studied by Borovkova et al (1992) were too sensitive and revealed differences even between isolates from the same virulence phenotype. However, in a study by Roeckel-Drevet et al (2003), RAPD-based analysis detected differences between isolates from distant geographical regions and showed low genetic variability among isolates in the same region, caused probably by bottleneck and founder effects. Intelmann & Spring (2002) performed RFLP studies of mitochondrial DNA and used simple sequence repeats and microsatellites as primers for the PCR.…”

“…However, in a study by Roeckel‐Drevet et al . (), RAPD‐based analysis detected differences between isolates from distant geographical regions and showed low genetic variability among isolates in the same region, caused probably by bottleneck and founder effects. Intelmann & Spring () performed RFLP studies of mitochondrial DNA and used simple sequence repeats and microsatellites as primers for the PCR.…”