Oca: Crunching the numbers on 2 years of oca from seed

Last week, I answered the most frequently asked question that I receive about oca.  This week, I am taking on the second most common question: What are the odds that I will get a variety worth keeping from oca seed?

Oca, as an octaploid, is a fundamentally heterozygous plant.  Every oca seed produces a different result and the variability is considerable, even when all the seeds come from the same cross.

Here is a sampling of varieties obtained from the Hopin x Mexican Red cross:

See what I mean?  A couple of varieties look a lot like Hopin.  None of them look much like Mexican Red.  And most of them look nothing like either parent.  Yield ranges from 99 to 854 grams.  Plant characteristics and flavor vary to a similar degree.

Without even crunching any numbers, you can see that there are a few in this group that are probably keepers and a few that should be discarded.

Yield is one of the more important criteria in the evaluation of new varieties.  Of course, they should also taste good, flower well, and have good tolerance to different environmental conditions, but if the yield isn’t good, none of the other characteristics are particularly compelling.  I took the yields for the 41 heirloom varieties that we grow and divided them into percentiles.  The 95th percentile for yield among heirlooms was 911 grams (almost exactly 2 pounds) and contained 3 varieties: Sunset, Hopin, and White.  This seems like a good goal, although I hope that we can eventually produce varieties that produce 2kg or more.

So, what are the odds that a new variety from seed will have a top yield?

Out of 601 varieties, 5 reached the 95th percentile of heirloom yield (two of those significantly exceeding it).  That’s 0.83%.  That may not sound encouraging, but it really isn’t bad at all.  1 out of 120 seedlings performed as well as the best heirlooms.  The 60th percentile was 433 grams, which, for the metrically challenged, is close to a pound.  So, about 1 in 3 seedlings yielded 1 pound or more per plant.  If you also want a tuber of a certain color, excellent flavor, and abundant flowering, you will exclude a lot of these plants, but the odds that a home gardener growing a few dozen plants will turn up several keepers seems very good.