Buckeye Gold (Taraxacum kok-saghyz, also known as rubber dandelion, and rubber root) is a species of dandelion that is of commercial interest for the high quality rubber produced in its roots. However, it is a slow growing species that competes poorly with Ohio weeds in field plantings, and chemical broadleaf herbicides also kill most of the plants. In order to overcome these agronomic shortcomings, scientists are developing herbicide-resistant varieties by a number of methods, including selection, transgene insertion, and gene editing. However, the release of such germplasm raises the question of gene flow between Buckeye Gold and its ubiquitous weedy cousin, the common dandelion (T. officinale). Could herbicide resistance in Buckeye Gold transfer to common dandelion?
Can Buckeye Gold and common dandelion interbreed?
We have surveyed common dandelions around the world. In North America, we have found only triploid obligate apomictic common dandelion plants. These produce clonal seed with exactly the same chromosomes as the mother dandelions. Thus, common dandelions cannot be fertilized by pollen from the rubber dandelion, which is a sexual diploid, like people. However, because rubber dandelions produce seed with two sets of chromosomes, one from the mother and the other donated by pollen from a father plant, it may still be possible for common dandelion to pollinate Buckeye Gold dandelion.
To address this possibility, unidirectional reciprocal crosses were conducted and progeny were evaluated with molecular markers. In addition, natural hybridization was quantified in plants produced by seed collected from Buckeye Gold plants grown in open sided greenhouses surrounded by natural common dandelion infested meadows over three years (~3.35 million Buckeye Gold plants in all). Hybrids were only detected during one of these years, at a rate of one in 100,000, when pollination was augmented with bee hives. Common dandelion pollen, from a number of mothers, used to fertilize Buckeye Gold flowers, produced low seed set and seeds with a low germination rate.
The very rare, true hybrid progeny, from both natural and deliberate methods, looked more like common dandelion (thin, yellowish green, lacerate leaves), than rubber dandelion (thick, bluish green, slightly lacerate leaves). Only a few of the hybrids produced viable (clonal) seeds, whereas the rest were sterile. Seeds produced by these apomictic hybrids established and produced apomictic progeny when in competition with perennial rye grass in planting boxes, similarly to common dandelion, which the weaker Buckeye Gold could not do.
What does it mean?
In conclusion, gene transfer to common dandelion via Buckeye Gold pollen, appears not be possible. In the opposite direction, very rare hybrids produced by Buckeye Gold mothers pollinated by common dandelion fathers cannot accept pollen from either dandelion species, and so cannot backcross into common dandelion. This means that it does not appear possible to transfer herbicide resistance from potential herbicide resistant Buckeye Gold varieties to the common dandelion. However, the ability of very rare, potentially herbicide resistant, hybrids to persist and become weedy is not yet known.
The scientific article behind this report may be accessed at Ecosphere 9(2):e02115. Doi: 10.1002/ecs2.2115
Katrina Cornish, is a joint Professor in Horticulture and Crop Sciences and Food Agricultural and Biological Engineering. She can be reached at 330-263-3982, or firstname.lastname@example.org. This column is provided by the OSU Department of Food, Agricultural and Biological Engineering, OSU Extension, Ohio Agricultural Research & Development Center, and the College of Food, Agricultural and Environmental Sciences.