Contrasting Patterns of Genetic Diversity and Population Structure ofArmillaria melleasensu stricto in the Eastern and Western United States

Abstract

Armillaria mellea infects hundreds of plant species in natural and managed ecosystems throughout the Northern hemisphere. Previously reported nuclear genetic divergence between eastern and western U.S. isolates is consistent with the disjunct range of A. mellea in North America, which is restricted mainly to both coasts of the United States. We investigated patterns of population structure and genetic diversity of the eastern (northern and southern Appalachians, Ozarks, and western Great Lakes) and western (Berkeley, Los Angeles, St. Helena, and San Jose, CA) regions of the United States. In total, 156 diploid isolates were genotyped using 12 microsatellite loci. Absence of genetic differentiation within either eastern subpopulations (theta(ST) = -0.002, P = 0.5 ) or western subpopulations (theta(ST) = 0.004, P = 0.3 ) suggests that spore dispersal within each region is sufficient to prevent geographic differentiation. In contrast to the western United States, our finding of more than one genetic cluster of isolates within the eastern United States (K = 3), revealed by Bayesian assignment of multilocus genotypes in STRUCTURE and confirmed by genetic multivariate analyses, suggests that eastern subpopulations are derived from multiple founder sources. The existence of amplifiable and nonamplifiable loci and contrasting patterns of genetic diversity between the two regions demonstrate that there are two geographically isolated, divergent genetic pools of A. mellea in the United States.

About Ganoderma boninense in oil palm plantations of Sumatra and peninsular Malaysia: Ancient population expansion, extensive gene flow and large scale dispersion ability

“…Results from Bayesian assignment tests in STRUC-TURE and AMOVA support the hypothesis that isolates from both regions originate from a single population, which indicates continual gene flows between those two regions in spite of the Malacca strait. This phenomenon of broad-scale basidiospore dispersal across 160e2000 km has also been observed for the well-known white rot basidiomycete Armillaria mellea in Northern America (Baumgartner et al 2010;Travadon et al 2012b). On the other hand, spatial autocorrelation results confirmed an over-dispersion between plantations (significant p-value for distance between 200 and 700 km) but also showed a shorterdistance dispersal pattern, with similar alleles found at distances of 0e10 km, i.e.…”

“…Such a large effective population size is consistent with the fact that G. boninense may have a wide host spectrum, like many white rot fungi (Baumgartner et al 2010;Woodward et al 1998). However, estimations of population size and of time expressed in generation numbers should be viewed with caution as G. boninense probably has overlapping generations.…”

“…However, a more precise estimation of clonal duplication events should be made in future, as we sampled only one isolate per oil palm and careful sanitation measures are taken in industrial plantations in order to avoid root-to-root contamination. The spreading pattern of G. boninense appears to be very different from A. mellea, another model of perennial crop root rot basidiomycete, which has a wide host spectrum and mainly spreads by vegetative multiplication (Prospero et al 2008;Baumgartner et al 2010;Travadon et al 2012 b). As previously shown by Pilotti et al (2003), G. boninense's dispersal mechanism seems more similar to that of Heterobasidion annosum, a Polyporales-like white rot fungus which is responsible for serious losses in conifer forests in the northern temperate regions (Woodward et al 1998) and has a predominantly sexual reproduction pattern.…”

“…Wood rot fungi form one of the main classes of phytopathogenic fungi and are responsible for major economic losses in perennial crops, as with the well-known Armillaria mellea which causes white rot on conifers (Prospero et al 2008;Baumgartner et al 2010). While wood decay fungi display a wide diversity of wood decay strategies (Riley et al 2014), species of the genus Ganoderma are characterized by their extensive wood delignification capacities (Otjen & Blanchette 1987;Rios & Eyzaguirre 1992).…”

Best Practices for Population Genetic Analyses

“…Markers with high mutation rates such as microsatellites (also known as simple sequence repeats or SSRs) provide insights into recent divergence (Atallah et al 2010;Baumgartner et al 2010;Berbegal et al 2013;Dunn et al 2014;Dutech et al 2010;Goss et al 2009b), whereas mitochondrial, nuclear or other sequence loci provide inferences about the more distant evolutionary history given the slower mutation rates Goss et al 2009a;Malvarez et al 2007;Schoebel et al 2014;Stukenbrock et al 2007).…”