Is variation in susceptibility to Phytophthora ramorum correlated with population genetic structure in coast live oak ( Quercus agrifolia )? (original) (raw)
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New Phytologist, 2004
• California coastal woodlands are suffering severe disease and mortality as a result of infection from Phytophthora ramorum. Quercus agrifolia is one of the major woodland species at risk. This study investigated within-and among-population variation in host susceptibility to inoculation with P. ramorum and compared this with population genetic structure using molecular markers. • Susceptibility was assessed using a branch-cutting inoculation test. Trees were selected from seven natural populations in California. Amplified fragment length polymorphism molecular markers were analysed for all trees used in the trials. • Lesion sizes varied quantitatively among individuals within populations, with up to an eightfold difference. There was little support for population differences in susceptibility. Molecular structure also showed a strong within-population, and weaker among-population, pattern of variation. • Our data suggest that susceptibility of Q. agrifolia to P. ramorum is variable and is under the control of several gene loci. This variation exists within populations, so that less susceptible local genotypes may provide the gene pool for regeneration of woodlands where mortality is high.
2015
correlated with population genetic structure in coast live oak ( Quercus agrifolia
Genetic epidemiology of the Sudden Oak Death pathogen Phytophthora ramorum in California
Molecular Ecology, 2009
A total of 669 isolates of Phytophthora ramorum, the pathogen responsible for Sudden Oak Death, were collected from 34 Californian forests and from the ornamental planttrade. Seven microsatellite markers revealed 82 multilocus genotypes (MGs) of which only three were abundant (>10%). Iteratively collapsing based upon minimum F ST , yielded five meta-samples and five singleton populations. Populations in the same metasample were geographically contiguous, with one exception, possibly explained by the trade of infected plants from the same source into different locations. Multidimensional scaling corroborated this clustering and identified nursery populations as genetically most distant from the most recent outbreaks. A minimum-spanning network illustrated the evolutionary relationships among MGs, with common genotypes at the centre and singletons at the extremities; consistent with colonization by a few common genotypes followed by local evolution. Coalescent migration analyses used the original data set and a data set in which local genotypes were collapsed into common ancestral genotypes. Both analyses suggested that meta-samples 1 (Santa Cruz County) and 3 (Sonoma and Marin Counties), act as sources for most of the other forests. The untransformed data set best explains the first phases of the invasion, when the role of novel genotypes may have been minimal, whereas the second analysis best explains migration patterns in later phases of the invasion, when prevalence of novel genotypes was likely to have become more significant. Using this combined approach, we discuss possible migration routes based on our analyses, and compare them to historical and field observations from several case studies.
Consequences of Phytophthora ramorum Infection in Coast Live Oaks1
2000
Sudden oak death, caused by Phytophthora ramorum, has infected and killed large numbers of oaks (Quercus spp.) and tanoaks (Lithocarpus densiflorus) in California since the mid 1990s. Since March 2000 we have been investigating the interactions between patterns of disease progression and broader landscape-scale patterns of disease incidence and expansion in study plots in Marin County. The incidence of new
Seasonal trends in response to inoculation of coast live oak with Phytophthora ramorum
We developed a branch cutting inoculation method to provide a controlled system for studying variation in response to inoculation of coast live oak (Quercus agrifolia) with Phytophthora ramorum. This method has advantages over inoculations of trees in the field, in containing the inoculum and in allowing high levels of replication and the possibility of time series of responses. We previously reported significant tree-to-tree variation, with little population variation in lesion size using this method (Dodd and others 2005). Here we report on a time series in which branch cuttings were