An Oryzalin Induced Polyploid From a Hybrid of Hibiscus Acetosella x H. Radiatus (Malvaceae) Exhibits Reduced Fertility and Altered Morphology

Hibiscus L. section Furcaria DC is a circumglobal group comprised of more than 100 species, many of which have potential for use as ornamentals primarily due to large showy flowers.  Two species of interest are H. radiatus Cav. and H. acetosella Welw. ex Hiern.; both of which are tetraploid (4x) with the genome composition AB.  Selection of H. acetosella has led to the development of several cultivars including ‘Panama Red’ PPAF.  These two species were hybridized to develop ‘Panama Bronze’ PPAF.  Response to these cultivars has been positive but a more compact habit is desirable.  Therefore, research was initiated to develop more compact forms through induced polyploidization.  Seed from crosses between H. acetosella and H. radiatus were germinated and treated with oryzalin at the cotyledon stage.  As plants grew they were visually evaluated for signs typical of induced polyploidy.  Several plants were identified as potentially doubled and were further evaluated using flow cytometery.  Three plants were identified as polyploid, including one octoploid (8x) and two cytochimeras (4x + 8x).  The cytochimeras, also referred to as mixoploids, were further investigated in an attempt to determine which histogenic layer(s) were doubled.  Stomatal measurements and flow cytometry of roots revealed the histogenic composition of the mixoploids to be 4-x-4 and 4-x-4+8, respectively.  The mixoploids have yet to flower, preventing analysis of the LII.  The octoploid (AABB) exhibits a number of typical phenotypic effects of induced polyploidy such as thicker and darker leaves (RHS N186A), larger stomata, and shorter internodes.  Field evaluation replicated in multiple locations to determine plant height will be conducted in 2009.  The octoploid exhibits greatly reduced fertility, likely due to increased frequency of multivalents during gametogenesis.  There has been no autonomous seed set observed in the octoploid as seen in tetraploids.  Also, there was low seed set obtained through controlled crosses with no germination to date, indicating that the octoploid may be functionally female sterile.  Controlled crosses are ongoing to determine levels of male and female fertility.  The current research shows that oryzalin is effective at inducing polyploidy in Hibiscus sect. Furcaria and represents the first time it has been used to induced polyploidy in the section.  Furthermore, induced polyploids from hybrids of H. acetosella and H. radiatus exhibit a more compact habit and reduced fertility, the latter being an important trait for expanding the market to extreme southern regions where it is perennial and could potentially become invasive.