Yacon: Seedling Progress

Last year, we grew two new yacon varieties from seed and also collected more than 1000 yacon seeds.  This year, after starting seeds in November, we have 132 yacon seedlings.  Because yacon is polyploid and an obligate outcrosser, each one of those seedlings will be a new variety.  That is, each variety must be pollinated by another variety; seeds are not produced where only one variety is grown.  The internal shuffling of multiple sets of chromosomes and the external mingling of parent genomes ensures that every seedling will be genetically distinct.

If you haven’t been following the story up until now, this is unusual.  Until very recently, yacon was considered to be nearly or fully sterile.  The few breeding programs have focused on laboratory manipulations like mutagenesis.  A 2014 research paper reported success with crosses between varieties and that inspired me to give seed production a more rigorous attempt.  We’re now seeing the fruits of that effort, with what I assume to be the first new yacon seedlings produced in North America in 2015 and 2016.  Ben Kamm at Sacred Succulents is also having success at this, so I think the future of open source & public domain yacon breeding looks bright.

With these seedlings, we know the female parents but not the male, as I crossed them repeatedly and indiscrimately in order to have the best odds of producing seed.  Seeds from four female parents germinated: Bekya (67 seedlings), Cajamarca (5 seedlings), Morado (8 seedlings), and New Zealand (52 seedlings).  The number of seedlings in each case is roughly proportional to the number of seeds that were produced.  Genetic diversity is probably fairly low, as only three varieties flowered in large numbers during the period when most of the seed was collected: Bekya, Morado, and New Zealand, which allows for only six combinations.  Toward the end of the season, all varieties flowered, so hopefully all 8 possible male parents are represented in the seedlings to at least a small degree.  I am surprised that there is no particularly strong differentiation between seedlings from different female parents.  They are all diverse in plant form and color.  New Zealand tends to balance green and purple in new growth, while Bekya is often strongly purple.  Bekya and Morado seedlings tend to be yellow-green in their mature foliage, while New Zealand is darker green.  Leaf shape and margin are extremely variable across all parents.

OC-16-1Ux02x05. New Zealand x OP. The strong contrast between green and purple in new growth appears to be more prevalent in seedlings out of New Zealand.
OC-16-1Ux03x05. Bekya x OP. In comparison to seedlings from New Zealand, seedlings from Bekya tend to have very strongly purple new growth.
OC-16-1Ux04x10. Bekya x OP. On the other hand, some seedlings out of Bekya show very little purple coloration.
OC-16-1Ux02x09. Bekya x OP. Strongly serrated leaf margines are not characteristic of Bekya, so perhaps this trait indicates pollination by another variety with this feature, such as Late Red.
OC-16-1Ux05x04. Morado x OP. Morado seedlings seem to develop more midrib coloration as they grow.

The first seedling emerged on November 28th and the last on May 6th, so there is about a 5 month difference in age between the oldest and the youngest.  This may prove interesting and possibly help to answer some questions about yacon’s life cycle.  Two of the oldest seedlings are now starting to flower.  I originally thought that yacon flowering was controlled by day length.  As I have grown more, I started to suspect that day length might be less of a factor or possibly none at all.  In some varieties, maturity seems to be more important, with flowering beginning at about six months.  Unfortunately, for outdoor plants, this timing coincides with late summer/early fall, so it is difficult to ascertain which factors are at work.  The June flowering of some of these 5 1/2 month old seedlings suggests that maturity may be the only factor involved.  It is also possible that these seedlings are unusual. although the fact that only the earliest are beginning to flower makes me think that this may just be the beginning and that we will see most of the seedlings flower as they reach about six months.

OC-16-1Ux02x03. New Zealand x OP. Seedling emerged November 28, 2015. Forming flower buds on June 8th.
OC-16-1Ux02x06. Bekya x OP. Emerged November 30th, 2015. Flower buds forming on June 8th.

Yacon grows very slowly here until the beginning of summer.  It is just starting to begin its real growth phase now.  The oldest plants are about 18 inches tall today.  In a month, they should be about four feet tall and, by the end of summer, anywhere from 5 to 7 feet tall.  The fact that they are flowering early may mean early senescence as well.  It will be interesting to see if the varieties that flower continue to grow or die back in summer.  This will give us some new data about aspects of yacon’s life cycle that have previously been unclear.

The real show will come in fall when we harvest all of these varieties.  We will be evaluating them for yield, skin and flesh color, and sugar concentration at harvest.  I particularly hope to see some of the colors that exist in South American varieties that are not available here, such as strongly orange, strongly purple, or pink flesh color.  Currently the plan is to grow all of them again next year for further evaluation.  We will also offer some of them through our Early Access Program.

You can see the full set of seedlings at our wiki.  (It is a big page and will take a while to load.  Probably not phone friendly.)

8 thoughts on “Yacon: Seedling Progress

  1. rowan.99 says:

    I am so excited about this project. Maybe in the future I may be able to buy some seeds and get some more diversity into the yacon here. I am amazed at what you are achieving :)

    • bill says:

      I hope that we will see seed formation without hand pollination this year with the very diverse patch of seedlings. If so, I will probably offer some of the seed. Fingers crossed!

  2. Filibert says:

    Is it possible to plant EARLY flowerers later in the season so that they bloom with the LATER flowerers and get seeds with even more genetic diversity?

    Are there any other closely related species that could be used to add genes to Yacon?

    • bill says:

      I don’t know yet if these are really early flowerers or if they are flowering as a consequence of maturity. The first seedlings germinated in November, so they might be reaching normal maturity. If so, that is a strike against the idea that yacon flowering is daylength dependent. We have to figure out what controls yacon flowering first. It could be simple maturity, day length, or a combination of these factors that is different from one variety to another. I hope that it turns out to be simple maturity, because plants could then be started in winter, leading to flowering in summer. This would be a lot more convenient. But if these plants are unusual in their earliness, then your idea would make it possible to cross them to late varieties.

  3. Filibert says:

    I checked around and there is only one Smallanthus specie naturally occurring in the USA; it is Yellow Bear’s Foot (Smallanthus uvedalius). I couldn’t find info on its ploidy or if it would cross with sonchifolia.

  4. Judith Bush says:

    You note that Smallanthus uvedalius doesn’t have storage tubers. Those that grow wild on my property in the Piedmont of North Carolina do have storage tubers. I’d be happy to ship you some along with some of the seed this fall.

    • bill says:

      That’s fascinating, Judith. Thanks for offering! I would love to get my hands on some rhizomes or seeds. That could be valuable breeding material.

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