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Title: Population structure in the genus Carya

item Grauke, Larry
item MENDOZA-HERRERA, M. - Texas A&M University

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2011
Publication Date: 5/1/2012
Citation: Grauke, L.J., Mendoza-Herrera, M.A. 2012. Population structure in the genus Carya. Acta Horticulturae. (ISHS) 948:143-158.

Interpretive Summary: We have studied a large collection of pecans and hickories from around the world using molecular markers. When we look at the pattern of those markers in relation to where samples originated, we see evidence that species are hybridizing when they grow together in a region, but are very different in different regions. Some of the differences between regions offer evidence about how long trees have been growing in those areas. Trees of one species may mix with trees of another species in one geographic area, but with trees of a third species in a different geographic area. Distribution maps help us keep track of where trees grow and which other trees they may be crossing with. Some of the adaptations that trees have to the soils or climate of a region might be shared among other trees in that region by crossing. We need to understand more about the wild relatives of our main target species in order to understand how the mixing of genes between those species may contribute to adaption. This information could help us in breeding better pecan trees. As we understand more about how the forest changes over space and time, we can do a better job of conserving forests as well as using them.

Technical Abstract: The genus Carya includes diploid (n=x=16) and tetraploid (n=2x=32) species in the southeastern United States. Only diploid species are found in Mexico, including three (Carya illinoinensis, C. ovata, C. myristiciformis) also found in the U.S. One endemic (C. palmeri) is found only in Mexico. Several species (C. cathayensis, C. dabieshanensis, C. tonkinensis, C. hunanensis, C. kweichowensis), all putative diploids, are found only in Asia and are distributed from India, Thailand and Vietnam to eastern China. Interspecific hybrids have been described between diploid species pairs, tetraploid species pairs and between diploid and tetraploid species. Plastid and nuclear molecular markers have been used to confirm hybridity in many suspected interspecific hybrids, including sympatric populations of C. glabra and C. floridana collected in Florida where hybridization creates genetic diversity between geographic populations of both species. Disjunct, geographically isolated populations of C. illinoinensis and C. ovata found in Texas offer resolution into the genetic bottlenecks that may preceed regional extinction. Populations include individuals regenerating from root sprouts so that multiple stems –at times the entire stand - are of a common genotype. Seedling accessions of C. cathayensis have been found to share a single molecular profile, raising questions of the genetic diversity present in this economically important Asian species. Interspecific hybridization with pecan has implications for long term maintenance of C. cathayensis, in light of the extensive recent establishment of pecan plantings