Showing papers by "Celeste C. Linde published in 2009"
TL;DR: Results imply that interacting selective and nonselective factors, acting across a broad range of scales, are important for the generation and maintenance of adaptively significant variation in populations of M. lini.
Abstract: Genetic variation for pathogen infectivity is an important driver of disease incidence and prevalence in both natural and managed systems. Here, we use the interaction between the rust pathogen, Melampsora lini, and two host plants, Linum marginale and Linum usitatissimum, to examine how host–pathogen interactions influence the maintenance of polymorphism in genes underlying pathogen virulence. Extensive sequence variation at two effector loci (AvrP123, AvrP4) was found in M. lini isolates collected from across the native range of L. marginale in Australia, as well as in isolates collected from a second host, the cultivated species L. usitatissimum. A highly significant excess of nonsynonymous compared with synonymous polymorphism was found at both loci, suggesting that diversifying selection is important for the maintenance of the observed sequence diversity. Agrobacterium-mediated transient transformation assays were used to demonstrate that variants of both the AvrP123 and AvrP4 genes are differentially recognized by resistance genes in L. marginale. We further characterized patterns of nucleotide variation at AvrP123 and AvrP4 in 10 local populations of M. lini infecting the wild host L. marginale. Populations were significantly differentiated with respect to allelic representation at the Avr loci, suggesting the possibility of local selection maintaining distinct genetic structures between pathogen populations, whereas limited diversity may be explained via selective sweeps and demographic bottlenecks. Together, these results imply that interacting selective and nonselective factors, acting across a broad range of scales, are important for the generation and maintenance of adaptively significant variation in populations of M. lini.
115 citations
TL;DR: It is concluded that the majority of R. secalis populations have experienced human-mediated migration that led to numerous and relatively recent founder events around the world.
76 citations
TL;DR: It is hypothesized that the pathogen only recently moved out of its centre of origin, resulting in founder populations that are reproductively isolated due to the contemporary absence of long‐distance gene flow.
Abstract: A phylogeographical analysis of the scald pathogen Rhynchosporium secalis was conducted using nuclear DNA sequences from two neutral restriction fragment length polymorphism loci and the mating-type idiomorphs. Approximately 500 isolates sampled from more than 60 field populations from five continents were analysed to infer migration patterns and the demographic history of the fungus. Migration rates among continents were generally low, consistent with earlier reports of significant population subdivision among continents. Northern Europe was mainly a source population for global migration. We hypothesize that the pathogen only recently moved out of its centre of origin, resulting in founder populations that are reproductively isolated due to the contemporary absence of long-distance gene flow.
45 citations
TL;DR: The results demonstrated that S. sclerotiorum populations in northern Iran, are randomly mating and have a number of shared haplotypes among regional populations; this possibly represents recent founder populations and/or a high occurrence of anthropogenic migration of infected plant material among populations.
Abstract: The genetic structure of 276 Sclerotinia sclerotiorum isolates representing 37 field populations from four provinces in northern Iran were analysed with six polymorphic microsatellite loci. In total, 80 haplotypes were detected with 19 haplotypes (23.7%) shared amongst at least two regional populations. None of the haplotypes were shared among all four regional populations. Of the 80 haplotypes, 32 haplotypes (40%) occurred in low frequencies represented by only one isolate. Moderate levels of gene diversity (H = 0.51 to 0.61) and genotypic diversity (Ĝ = 12.0 to 22.0; clonal fraction = 0.39 to 0.67) for regional populations were observed. Genotypic diversities (Ĝ) did not differ significantly among populations. All regional populations were in linkage equilibrium indicating the occurrence of outcrossing. Low to moderate levels of population subdivision (0.03 to 0.07), were observed among regional populations. Only one large panmictic population was inferred by Structure, indicating no significant population structure. A Mantel test showed no significant isolation by distance (r = −0.43; P = 0.18), indicating anthropogenic movement of inoculum. The results demonstrated that S. sclerotiorum populations in northern Iran, are randomly mating and have a number of shared haplotypes among regional populations; this possibly represents recent founder populations and/or a high occurrence of anthropogenic migration of infected plant material among populations.
44 citations
TL;DR: A high degree of conservation for the cytb gene is indicated at both intra- and interspecific levels, and complete QoI sensitivity in all R. secalis populations tested.
Abstract: Barley scald caused by Rhynchosporium secalis is often controlled by fungicides, most recently by those in the strobilurin-based (QoI) class. Since the launch of QoIs in 1996 a range of important plant pathogens, including Blumeria graminis, Mycosphaerella fijiensis and Plasmopara viticola, developed resistance. Present monitoring data indicate that R. secalis populations remain sensitive. The primary molecular mechanism of QoI resistance in several fungi is a point mutation at codon 143 in the mitochondrial-encoded cytochrome b gene (cytb), which causes the substitution of glycine by alanine (G143A). We characterised the cytb gene of R. secalis, assessed the intraspecific and interspecific sequence diversity, developed a PCR-RFLP diagnostic tool to detect the most common allele associated with QoI resistance, screened a global collection of 841 R. secalis isolates for this allele and tested a representative sample of isolates for QoI resistance in vitro. The results indicated a high degree of conservation for the cytb gene at both intra- and interspecific levels, and complete QoI sensitivity in all R. secalis populations tested.
15 citations
TL;DR: Five highly variable loci were found to amplify reliably in U. mjoebergi, although one locus exhibited evidence for the presence of null alleles, and two loci exhibited evidence of linkage.
Abstract: Microsatellite markers were developed for the fiddler crab Uca mjoebergi for use in paternity assignment. Five highly variable loci were found to amplify reliably in U. mjoebergi, although one locus exhibited evidence for the presence of null alleles, and two loci exhibited evidence of linkage. The number of alleles, expected heterozygosity and probability of paternity exclusion (P > 0.999) suggest that these markers when combined provide sufficient power to determine paternity by exclusion in this species. Three primer pairs were found to also amplify PCR products from three additional fiddler crab species (U. dampieri, U. flammula and U. seismella), and will prove useful for phylogeography and behavioural ecology of fiddler crabs.
10 citations