Abstract of Peter Zale's colloquium, presented to the Department of Horticulture and Crop Science on 26 January 2011
Interspecific hybridization in Phlox: Analysis of genetic diversity, relatedness, and crossing barriers
ABSTRACT: Phlox is a genus of 65 species indigenous to the U.S.A.; 22 highly variable species are native to the central and eastern states. These species are classified into three clades based on phylogeny, karyology, and phenotypic characteristics. Among these eastern taxa, Phlox paniculata has been widely cultivated for two centuries throughout temperate regions of the world resulting in the development of numerous cultivars. Some of these cultivars have probably arisen through interspecific hybridization, but information on their origins is minimal, comparatively few of them remain in cultivation, and accuracy of taxonomic identity is questionable. However, recent phylogenetic and ecological studies have implicated interspecific hybridization as a major driver of evolution in eastern Phlox species, suggesting that barriers to the exchange of genetic information between at least some species are few and weak. While the potential for interspecific hybridization in Phlox is clear, the extent to which it can be manipulated for improvement of horticulturally-desirable traits has yet to be defined. Recombination of phylogenetically related Phlox genomes has the potential to generate Phlox cultivars that display a prolific blooming habit, flower over a longer time period, display novel plant habits (novel color forms, compact vs. tall plants), and are disease resistant (especially to powdery mildew and leaf black spot). The primary objective of this research is to clearly define interspecific crossing barriers which lead to the development of gene pools describing hybridization between Phlox paniculata and related taxa from each of the three eastern Phlox groups. To achieve this goal, a core collection of 243 accessions, comprising both feral and cultivated taxa, has been assembled at the Ornamental Plant Germplasm Center. Molecular markers (SSRs) will be developed for each accession using previously-defined primers specific for Phlox; these markers will aid in establishing relatedness between the accessions, provide an assessment of the genetic diversity within this core collection, and also facilitate identification of hybrid progeny in both intra- and inter-specific crosses. Hybridization experiments within P. paniculata as well as between P. paniculata and selected eastern Phloxtaxa will be conducted during 2011 and 2012. Temporal separation of flowering between P. paniculata and other eastern Phlox taxa will require supplemental studies concerning pollen storability and manipulation of flowering times necessary to perform desired crosses. Phenotypic character analysis will also be used for hybrid confirmation. Resultant progeny will be used in further hybridization studies to test for hybrid sterility, and the inheritance of desirable ornamental and disease resistance characteristics, and to determine germplasm collection priorities that target Phlox populations exhibiting desirable characteristics. Our studies will likely identify the more promising interspecific combinations of Phlox that may eventually result in novel horticultural products.