Those of you who glaze over at the sight of charts, figures and arcane jargon may prefer to look away now. Please don't - I won't detain you long.
Ben Gabel of Real Seeds mentioned to me that the crops planted in a bed which had contained oca the previous year seemed to grow less well than expected. My curiosity piqued, I decided to boldly head off at warp factor 10 to the planet Allelopathy.
Allelopathy is one of those concepts in plant science and horticulture that seems to engender a lot of heat, but surprisingly little light. It is, as interesting ideas often are, contentious. Reputations have risen and fallen; promising careers have ended in derision and ignominy. Hans Molisch, who published the first definition of allelopathy in his book Der Einfluss einer Pflanze auf die Anderd-Allelopathie (The Influence of one Plant on Another-Allelopathy) in 1937 - died the same year - suspicious or what?
So what is allelopathy and what's it got to do with oca? Allelopathy is the inhibition of one plant by the chemicals released by another. It's chemical warfare. That's one definition, or maybe two and they'll do for the purposes of this discussion.
Well, knowing a little bit about oca's biochemistry, I wondered whether some of the weird and wonderful compounds it contains might be responsible for these effects. Ones like ocatin, harmine, harmaline and those good old standbys - fluorescent β-carbolines.
So I did a quick bioassay, the so-called "Sandwich Method" using dried oca leaves, some agar and lettuce seeds. The dried leaf material was embedded in the agar and the lettuce seeds sown on the agar surface. Then the whole lot, including a control (no leaf material) were incubated for a few days at 20 C.
Here are the results, recorded as percentage elongation of lettuce roots (radicles) compared to the control:The results seem to indicate that oca leaf material exerts a powerfully inhbitory effect on lettuce root elongation. I'll say one thing though. I'd rather spend my time measuring lettuce radicles than trying to import Excel charts into this blogument. They say practice makes perfect, but strangely, not in my case..........
So perhaps what Ben noticed could be the result of allelochemicals leaching from the leaves or being exuded from the roots. Maybe these chemicals have an inhibitory effect on competitors or following crops. Maybe this is allelopathy. I don't know, but it is interesting and is worth serious investigation. I am available and my rates are very reasonable.