Tuesday, October 28, 2014

Sunflower crosses.

Last year I crossed the perennial (tuber-forming) sunflower Helianthus tuberosus (image #1) to an annual sunflower H. annuus "Russian Mammoth". I used the much larger, 1ft wide, flower of "Russian Mammoth" (image #2) to pollinate as many of the tiny H. tuberosus flowers as I could.

2. H. annuus "Russian Mammoth".
1. H. tuberosus & seeds.
At the end of the season, I collected ~70 seeds from the H. tuberosus seed heads. Many seed heads had already been destroyed by the local birds which resulted in some scattered seed.

Squirrels got to the seed heads of the "Russian Mammoth" (image #2), because I later put them out in the sun to dry. As a result, I don't have the many more seeds of this variety I was expecting to have. Fortunately, the variety has been available since roughly 1870 and should be easy to find more seeds for.

3. Giant hybrid.
I didn't plant any of the seeds I collected from the H. tuberosus plant, since I would be moving before the plants had matured. However, three of the seeds that the birds had scattered managed to grow up out of the weed patch. Of these, two were obviously hybrids (they had traits found separately in both parents). One of the hybrid plants has a thin stem and flopped over (yellow flowers at lower-left in image #3), even with my efforts to keep it upright. The second hybrid has a robust stem that has let it withstand all the wind and rain of this season. So far, this plant is pretty much exactly what I was hoping the F1 hybrid plant would be.

I finally got a picture of me (6'4") standing next to the hybrids yesterday. Both hybrid plants are still green and thriving, even though the H. tuberosus plants have all shut down for winter. Once we get a killing freeze, I'll cut down the plants and dig up any tubers they've produced.

With luck I'll be able to collect some F2 seed off these plants, but since I no longer live where the plants are, I'm expecting the birds to get to them before I do. As the F1s are supposed to produce tubers generally, I should be able to regrow these plants next year from the tubers they are now likely to be producing.

4. en.wikipedia.org/wiki/Perennial_sunflower
The sunflower genus (Helianthus) contains a wide range of species. Some species are difficult to cross, while others will cross readily. Image #4 illustrates the use of hexaploid species to break down reproductive barriers between annual and perennial diploid species (at left and right). Crossing the tetraploid hybrids to either parent type results in uneven chromosome sets and high rates of infertility due to aneuploidy. The tetraploids can easily cross, however, allowing genes from diverse sources to be recombined in their progeny.

5. www.edenbrothers.com
The common sunflower (H. annuus) has been bred to produce a range of colors in addition to the yellow of wild sunflowers (such as those in image #5). The genes for these color changes could be added to a perennial sunflower using the same method I'm using to add traits for giant growth. (Someone else has this project under way.)

Because of the differences in ploidy between the annual sunflowers from the commonly available perennial (H. tuberosus), it would likely be in the F3 generation or later before such rich colors could be regained. This is discussed in the link below.