Inheritance of two mutant foliage types, variegated and purple, was investigated for diploid, triploid, and tetraploid tutsan (Hypericum androsaemum). The fertility of progeny was evaluated by pollen viability tests and reciprocal crosses with diploids, triploids, and tetraploids and germinative capacity of seeds from successful crosses. Segregation ratios were determined for diploid crosses in reciprocal di-hybrid F1, F2, BCP1, and BCP2 families and selfed F2s with the parental phenotypes. F2 tetraploids were derived from induced autotetraploid F1s. Triploid segregation ratios were determined for crosses between tetraploid F2s and diploid F1s. Diploid di-hybrid crosses fit the expected 9: 3: 3: 1 ratio for a single, simple recessive gene for both traits, with no evidence of linkage. A novel phenotype representing a combination of parental phenotypes was recovered. Data from backcrosses and selfing support the recessive model. Both traits behaved as expected at the triploid level; however, at the tetraploid level the number of variegated progeny increased, with segregation ratios falling between random chromosome and random chromatid assortment models. We propose the gene symbol var (variegated) and pl (purple leaf) for the variegated and purple genes, respectively. Triploid pollen stained moderately well (41%), but pollen germination was low (6%). Triploid plants were highly infertile, demonstrating extremely low male fertility and no measurable female fertility (no viable seed production). The present research demonstrates the feasibility of breeding simultaneously for ornamental traits and non-invasiveness.
Richard T. Olsen, Thomas G. Ranney and Dennis J. Werner
Clara E. Trueblood, Thomas G. Ranney, Nathan P. Lynch, Joseph C. Neal and Richard T. Olsen
Although Hypericum androsaemum L. is a valuable landscape plant, the species can be weedy and potentially invasive in certain locations. Infertile, non-invasive cultivars of H. androsaemum with desirable ornamental features would be ecologically beneficial and valuable for the horticultural industry. The male and female fertility of 10 triploid H. androsaemum, developed with a combination of variegation and foliage colors, was investigated under greenhouse (controlled pollination) and field conditions (natural pollination). Male fertility was evaluated based on pollen viability tests (pollen staining and pollen germination). Female fertility was based on fruit set, seed set, germinative capacity of seeds, and number of seedlings produced for each flower. Although values for different measures of fertility varied among triploid clones, pollen germination was significantly reduced for all triploids and nine of the 10 triploids produced no viable seed. These results represent 100% failure of ≈171,000 potential fertilization events based on fertility levels of diploid controls. The remaining triploid clone produced two seedlings per flower compared with 260 seedlings per flower for the controls. However, the seedlings produced by the triploid clone died shortly after germination. This research documented that the triploid H. androsaemum tested are highly infertile with no measurable female fertility. These clones will provide ideal alternatives to fertile forms of H. androsaemum where invasiveness is a concern. These methods also provide a useful protocol for evaluating fertility of other taxa that are selected or developed as non-invasive cultivars of potentially weedy species.
Richard T. Olsen and Thomas G. Ranney
Inheritance of two mutant foliage types (purple and mottled variegated) was investigated for diploid, triploid, and tetraploid tutsan (Hypericum androsaemum). Segregation ratios were determined for diploid crosses in reciprocal dihybrid F1 and F2, BC1P1, and BC1P2 families. F2 tetraploids were derived from autotetraploid F1s. Triploid segregation ratios were determined from crosses between autotetraploid F1s and diploid F1s. Diploid di-hybrid crosses fit the expected 9:3:3:1 ratio for a single, simple recessive gene for both traits, with no evidence of linkage between each trait. Data from backcross and triploid crosses generally supported this model. In tetraploid crosses we observed twice as many variegated phenotypes as predicted which was not explained by random chromosome or chromatid assortment. Inheritance of purple foliage did not deviate from random chromosome assortment at the tetraploid level.
Whitney D. Phillips, Thomas G. Ranney, Darren H. Touchell and Thomas A. Eaker
valuable nursery crops, but potentially weedy in some environments, including trumpet vine ( Campsis ×tagliabuana ) ( Oates et al., 2014 ), tutsan ( Hypericum androsaemum ) ( Trueblood et al., 2010 ), maiden grass ( Miscanthus sinensis ) ( Rounsaville et al