The 2012 ASHS Annual Conference

Interspecific hybridization has played a role in the development of improved Phlox cultivars, but thorough delineation of sexual compatibility by systematic crossing experiments among the species is lacking.  Over 60 species of Phlox native to North America, and of these, 25 are native to the eastern United States.  Despite the economic importance of a few of these well-defined eastern species, this group also contains many highly variable, ornamental, and taxonomically muddled species whose interspecific crossing compatibility remains unrealized. To test such relationships, we have implemented a crossing scheme between numerous genotypes of the 25 phlox species native to the eastern United States. utilizing germplasm that includes wild collected and cultivated material. Thus far, we have completed over 15,000 pollinations comprising over 500 cross combinations performed in a partial diallel. Attempts have been made to recreate putative horticultural and naturally occurring hybrid taxa described in the literature.  A minimum of 50 pollinations per reciprocal cross has been performed. Success of a given cross is heavily influenced by phylogenetic relationships and style length.  Crosses between short-styled species within section Divaricatae generally have a high rate of success when made in both directions, although crosses involving some wild-collected genotypes of P. amoena and P. floridana are only successful when these species are used as female parents.   This may be due due to cytoplasmic effects or differences in ploidy.  Hybridization between species in different sections have a low rate of success.  Crosses between P. paniculata (section Paniculatae) and P. carolina (section Ovatae), both long-styled, are only successful using the former as the female parent and only using selected genotypes.  Crosses between long and short-styled taxa generally fail to produce seed; only the cross of Phlox drummondii x Phlox paniculata has produced seed.  The hybrid nature of the progeny from this cross has yet to be determined.  A panel of 10 microsatellite (SSR) and various flower and leaf morphological markers measured using Tomato Analyzer software are being used to assess putative hybrids.   Assessment of hybrid fertility to produce advanced generations is ongoing.