Return of the Sunflower

A few years ago I made a cross between a sunflower (var. "Russian Mammoth") and a sunchoke (probably var. "Stampede"). My goal was to eventually get a plant that produced tubers like the sunchoke, but was super-charged with the giant growth of the sunflower. The two species have different chromosome counts, which complicates things a bit.

2014

That first cross resulted in three F1 plants. I should have grown more, but it didn't work out that way. One of the plants grew to 10ft tall, with relatively large flowers, while the other two looked more or less like the sunchoke parent. I moved by the end of this season, but I was able to go back and recover root material from the plants. I then stored the roots in a fridge over the first winter and planted them at our new place when spring came around. Only the tubers produced from the largest plant survived this process.

Our current place has routine visitations by deer who seem to find sunflower leaves delectable. The first several shoots produced by the tubers were neatly trimmed to the ground. When I finally put together some protection for them, they succeeded in sending up one final shoot. That shoot topped out at about 2ft tall and produced a single small flower. This was a far-cry from the 10ft skyscraper the tuber had come from. I was so disappointed that I didn't even take any pictures of the little plant. I assumed the repeated early-season trimmings had dwarfed it and hoped it would do better the following year.

2016

I was better prepared for 2016. I made a 7ft tall chicken-wire cylinder to place around the growing plant. This kept the plant protected for most of the season. The cylinder was knocked over a couple times (either by storms or aggressive deer), but this only exposed the lower leaves to the hungry mammals. The plant grew to about as tall as the cage and bloomed, still well short of the 10 ft of the first year. Though the plant branched much more than the first year, it did so much less than the sunchoke parent.

Our new yard has lots of animal traffic besides the deer. Turkeys are commonly seen in the neighborhood, though we don't often see them in our yard.

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2017

I'm hoping the plant will do even better in 2017. Three clusters of new shoots have been coming up near where the plant was last year and I have a slightly wider protective cage put in place. The shoots are more widely spaced than they were last year. I'm hoping this means each individual stem will be larger/taller.

The plant produced abundant seeds in the first year, but has since then produced absolutely none. I'm pretty sure this means the plant inherited the self-incompatibility mechanism from its sunchoke mother. The first year there was plenty of pollen from its siblings, but there has been none the last couple of years.

There may be a few oilseed sunflowers around this year to contribute pollen, grown from scattered birdseed. My perennial sunflower is tetraploid, so any crosses to these diploids would produce highly sterile triploid offspring. These might be interesting to grow, but they wouldn't contribute to my overall goal.

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For my breeding goals to move forward, I'll need to produce more tetraploid F1s by crossing sunchoke and another giant sunflower. I don't have any sunchoke planted right now, so I probably won't be able to get flowers even if I did find some tubers soon. There are several giant sunflower varieties I could use to help make more F1s, but I'll probably keep using "Russian Mammoth" to simplify the overall genetics of the future F2s.


References:

• Earlier blog posts on sunflowers:
• the-biologist-is-in.blogspot.com/2014/10/sunflower-crosses.html
• the-biologist-is-in.blogspot.com/2014/10/genetics-in-sunflowers.html
• the-biologist-is-in.blogspot.com/2014/11/hybrid-sunflower-roots.html
• Background info on this cross:
• bulbnrose.x10.mx/Heredity/sunflowerXchoke/sunflowerXchoke.html

Hybrid sunflower roots.

1. Plant 3, roots & tuber.

A few weeks ago, we had a solid freeze and the sunflower season came to an end. I dropped by the old place and dug up my sunflowers to see if any of the F1s had developed tubers. The largest hybrid (plant 3) produced one skinny tuber, while the smaller two plants appeared to produce no tubers at all. This was a disappointment, but a more detailed examination of the remaining plant material led to some positive surprises.

2. Plant 1, seeds.

The first plant looked very much like the Helianthus tuberosus mother, but with more red pigment on the stems. I had assumed this was the result of some recombination of maternal alleles and was at best a control to compare the hybrid plants against. When I looked at the remaining two dried flowers on this plant and found them to be full of seeds (image #2), I realized this plant is likely to also be a hybrid.

3. Plant 3, root bud.

The plant that grew the tuber in image #1 also produced a second type of perennial structure, a new bud growing from the old root crown (image #3). This is a structure that isn't seen in either parent species. This feature has been observed before in crosses of this type, however, so I should have expected the possibility.

4. Plant 2, roots.

The other two plants had mildly-swollen roots (images #4 & #5) that have appeared alive when I checked on them. I don't know if they will show new growth in the spring, or if the roots will at some point finally start to rot.

5. Plant 1, roots.

I'm storing the tuber and all the root structures in a dedicated small cube-fridge over the winter. This should keep them safe from the mice that wander through my basement and allow me to grow at least one of them again next year alongside additional F1s from the ~70 seeds that remain from the first cross.

References:

1. H. annuss x H. tuberosus : bulbnrose.x10.mx/Heredity/sunflowerXchoke/sunflowerXchoke.html

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.

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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.

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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.

the-biologist-is-in.blogspot.com/2014/10/genetics-in-sunflowers.html

Genetics in Sunflowers.

Plant #1 (H. tuberosus).

Plant #1 leaf.

Last year I started a genetics experiment with sunflowers. I grew a perennial sunflower (Helianthus tuberosus) and an annual sunflower (H. annuus cv. "Russian Mammoth") and tried to cross them. I shook pollen from the very large H. annuus flower all over and around as many of the very small H. tuberosus flowers as I could. This cross has been done before ([1], [2], & [3]), but not necessarily with a giant variety like "Russian Mammoth" as the father variety. I was working under the assumption that I'd be able to recognize any hybrids.

At the end of the season, I dissected 12 seed heads and recovered approximately 70 seeds. I ended up not planting any seeds this year, as I knew I was moving to a new house and wouldn't be able to maintain the experimental plants.

As I was doing a final cleanup of my flat, I noticed a sunflower blooming out in the backyard. On closer examination, there were three sunflower plants poking up through the weed patch. The only sunflowers growing in the area last year were my experimental parents. The H. tuberosus mother was growing in a planter and the H. annuus father wasn't allowed to mature seeds in the garden, so I was pretty sure these sunflowers had grown from seeds dropped by the mother plant.

The first plant to bloom appears to be completely H. tuberosus, though it shows much more red in its stems than the mother.  The other two plants came into bloom later and appear to be hybrids.

There are several traits which distinguish H. tuberosus from H. annuus cv."Russian Mammoth":

Plant #3. H. tuberosus leaf margins extend down the entire petiole, while in H. annuus the leaf margin ends at the top of the petiole. All three plants showed the H. tuberosus version of this trait. H. tuberosus has an elongated leaf, while H. annuus has a wide leaf. The blooming plant showed the H. tuberosus version of this trait. The other two plants had leaves of an intermediate form. H. tuberosus flowers are very small, while H. annuus cv."Russian Mammoth" flowers are very large. The first plant to bloom has flowers the size of those on H. tuberosus. The other two plants now have flowers which are about twice as wide as those on H. tuberosus. H. tuberosus plants are highly branched with many flowers, while H. annuus cv."Russian Mammoth" has a single stem with a single terminal flower. The first plant to bloom has lots of side-branches and lots of flowers. The second plant to bloom has a few small side-branches and a few flowers. The third plant has no side-branches and a few additional flowers growing from leaf-axils. H. tuberosus plants have thin stems, while H. annuus cv."Russian Mammoth" plants have a very thick stems. The first two plants to bloom have thin stems and need support to stay upright. The third plant to bloom has a thick stem, capable of keeping it upright without support. H. tuberosus plants grow to near 6 feet tall, while H. annuus cv."Russian Mammoth" plants grow to near 11 feet tall. The first plants to bloom topped out below 5 feet tall. The second reached about 7 ft and the third reached over 8 feet tall before blooming. I'll get a better measurement of their height when they have died for the season. H. tuberosus produces underground tubers, while H. annuus does not. I'm waiting until frost has killed the plants before digging them up, so they have the best chance to produce tubers.

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Plant #3, showing winged petiole.

What predictions can we make about a cross between H. tuberosus and H. annuus? H. tuberosus is hexaploid and H. annuus is diploid, so the resulting hybrid will be tetraploid.

H. tuberosus is usually propagated by tubers, so it can contain lots of hidden genomic diversity across it's six sets of chromosomes. The progeny plant which appears to be completely H. tuberosus has much higher levels of red pigment in its stems, indicating heterozygosity is present in the H. tuberosus parent. H. annuus cv. "Russian Mammoth" is an annual variety that has been stable since 1880, which means it is highly inbred and therefore highly homozygous.

With this information, the cross would look something like:

A1A2A3A4A5A6 x BB

The resulting F1 progeny would be:

AaAbAcB

There are 20 potential combinations of three alleles of of the possible six homologs at a each locus of the 17-chromosome sets found in the H. tuberosus parent, so it isn't surprising that the two observed hybrids aren't entirely alike.

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Selfing the F1s...

AaAbAcB x AaAbAcB

…has all kinds of possible outcomes. If we simplify the calculation by assuming the H. tuberosus parent is homozygous, we get a cross...

AAAB x AAAB

…where half of the gametes are AA and the other half are AB. The Punnett square for this cross...

	AA	AB
AA	AAAA	AAAB
AB	AAAB	AABB

…shows there's no way to get an F2 which is homozygous for the alleles from the H. annuus parent. A goal of this project is to breed up a sunflower which has the tuber-generating trait of H. tuberosus and the super-sized growth of H. annuus cv. "Russian Mammoth". If I can isolate some F2s that appear AABB for some of the interesting traits, perhaps by isolating those that have the best tubers and the most overall growth, then I might later be able to select from F3 families which cover the whole range of allelic combinations at the loci important for these two traits. The Punnett square for selfing the AABB F2s...

	AA	AB	AB	BB
AA	AAAA	AAAB	AAAB	AABB
AB	AAAB	AABB	AABB	ABBB
AB	AAAB	AABB	AABB	ABBB
BB	AABB	ABBB	ABBB	BBBB

Plant #3 flower buds.

…shows the very diverse combinations expected at each locus. From such an F3 family, I would then have the best odds of selecting out a plant with several alleles driving tuber formation and driving extreme plant growth. The combination of which, I hope, would then result in extreme tuber production.

In a typical diploid cross, the F2 generation is where the most combinations of alleles appear and where selection is most important. In this example, it wasn't obvious before calculating through the probabilities that the F3 generation would be where the most combinations of alleles would appear.

Hopefully, the deer at my new place will leave my sunflowers alone for the years it will take to complete this project.

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References:

1. Encheva, J., M. Christov, and P. Ivanov (2003). Characterization of Interspecific Hybrids Between Cultivated Sunflower H. annuus L. (cv. Albena) and Wild Species Helianthus tuberosus. Helia 26: 43-50.   (http://www.doiserbia.nb.rs/img/doi/1018-1806/2003/1018-18060339043E.pdf)
2. http://bulbnrose.x10.mx/Heredity/sunflowerXchoke/sunflowerXchoke.html
3. Kantar, M. B., K. Betts, J. Michno, J. J. Luby, P. L. Morrell, B. S. Hulke, R. M. Stupar, and D. L. Wyse (2014). Evaluating an interspecific Helianthus annuss x Helianthus tuberosus population  for use in a perennial sunflower breeding program. Field Crops Research 155: 254-264 (http://experts.umn.edu/pubDetail.asp?id=84888291084&o_id=199&t=pm)

Information about traits from references and observations.

• Reference #2 indicates tuber formation is dominant in the F1s.
• Winged petioles are dominant in F1.
• Secondary branches are mostly dominant in F1. There seems to be allelic variation for this trait in the H. tuberosus parent.
• Large flower size is mostly recessive in F1.
• Tall growth is partly dominant in F1. There seems to be allelic variation for this trait in the H. tuberosus parent.