ARS | Publication request: Estimates of Spatial Genetic Structure within and among Clones of Wild Lowbush Blueberry in Maine using EST-PCR Molecular Markers

Submitted to: Meeting Abstract
Publication Type: Abstract
Publication Acceptance Date: August 10, 2008
Publication Date: August 21, 2008
Citation: Bell, D.J., Drummond, F.A., Rowland, L.J. 2008. Estimates of Spatial Genetic Structure within and among Clones of Wild Lowbush Blueberry in Maine using EST-PCR Molecular Markers. Meeting Abstract.

Technical Abstract: Using recently developed EST-PCR markers, several levels of spatial genetic structure of wild lowbush blueberry, Vaccinium angustifolium Ait., were investigated. Knowledge of this structure (or lack of it) is a prerequisite to testing hypotheses regarding the dramatic yield variation among individuals or clones as a possible result of near-parental inbreeding depression. Lowbush blueberry is largely self-incompatible since selfing rates are very low relative to outcrossing rates. This is well known in the literature and has been shown here, too, by three years of field hand-crosses among genotyped individuals in two fields in Maine. Leading researchers in lowbush blueberry have conjectured that perhaps closely spaced groups of highly related clones, who likely receive most pollen from themselves and their nearest neighbors (because of near-neighbor honey bee pollination patterns), could be a viable explanation of these dramatic differences in yield. If this hypothesis is true, one would expect to find these two properties of the system: 1) that structure does exist and that there should be indications of positive spatial autocorrelation within fields, i.e. clumping of related individuals who exchange pollen, and 2) that clusters are closely enough related to incite a decrease in yield due to inbreeding depression. The work presented here focuses on the first of these. We have attempted to break this structure into several logical levels: 1) intraclonal, 2) among clones within a field and 3) among three fields separated by 18 km. Data will be presented that shows that clones show high but not complete intraclonal fidelity. Also, transects within fields show that there is no correlation between genetic and physical distance of clones. Several analyses are presented including AMOVA (Analysis of Molecular Variance), Principal Component Analysis and various methods of spatial autocorrelation which all indicate a `trend¿ of isolation by distance only at longer distances between fields. In summary, our quantitative molecular evidence supports the characterization of the lowbush blueberry species as a `phalanx¿ clonal form with an `initial seedling recruitment¿ life history as opposed to `repeated seedling recruitment¿. Therefore, the structure that we currently see in the fields of these long-lived woody perennials could be the result of 13,000 years (last glaciation period in Maine) of long distance dispersal of seed (diploid gene flow) by birds and bears. This could have resulted in a random seed bank of individuals which then were allowed to colonize and take over fields that have been burned, cleared and harvested by mankind for several centuries. If true, these conclusions do not support the idea that proximal, highly related clones cause significant field level suppressions of yield by inbreeding depression. Subsequent and ongoing work in field hand pollinations are revealing that differences in selfing rate strongly predict general outcrossing yield and may be interacting with genetic relatedness in a complex dynamic.