2019 ASHS Annual Conference

Hardy hibiscus (Hibiscus moscheutos) is a native perennial plant with strong ornamental qualities such as large, showy flowers, continual summer blooming, and a rounded shrub habit. Hardy hibiscus (2n=38) is a pleasing landscape plant with a wide growing range (hardy in USDA zones 4a-9b), and reasonable fertility, producing many fruit and seed. To prevent reseeding and potentially extend the bloom period by eliminating fruit and seed production, the development of sterile plants was trialed. Sterile plants can be created by developing triploid progeny, which are typically sterile or have greatly reduced pollen viability. Eleven advanced, experimental lines and two commercial cultivars were used to obtain 12 families of intraspecific seed in summer 2016. Plants were chosen for aesthetic characteristics, such as red foliage, red stems and petioles, and compact or reduced size, and for enhanced tolerance of hibiscus sawfly (Atomacera decepta). Seed was sown in early spring 2017 and once the germinating seedlings had fully-expanded cotyledons, they were soaked in a 100 mM oryzalin solution on a rotary shaker for either two or four hours. A total of 594 seedlings were treated for two hours and 586 seedlings for four hours over nine different dates between 14 June and 17 Aug. 2017. Oryzalin was applied for its inhibitory effects on the spindle fibers during mitosis, thereby acting as a chromosome-doubling agent. Plants were allowed to recover and ploidy level was evaluated via flow cytometry in summer 2017. Plants having double the chromosome number of the species were used as female parents once they began flowering, and untreated, breeding lines were used as pollen parents in hand-pollinations made from Jan. to Sept. 2018 to produce triploid seed. Putative triploid seed was collected and seedlings were tested via flow cytometry. Seventy-five hibiscus plants from 11 crosses have been confirmed as triploid by flow cytometry and were planted in the field. Remaining putative triploid seed (2,000+) will be sown spring 2019 and resulting plants will be evaluated for triploid status and cultivar potential in summer 2019. Results show the applicability of developing triploid plants using polyploidy induction with chemical mutagens and triploid selections will be presented.