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.

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.

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.)