Saturday, January 12, 2013

More on Wheat Tillering

I described tillers on a previous post.  They are like little photo copies of that initial evolving wheat plant, emerging from the main stem, establishing roots, and growing upward alongside the parent plant.  Each of these offspring can themselves produce more tillers, giving each plant the potential for as many as fifty followers, though only 5 or 6 usually reach maturity, with 2 or 3 of them setting full spikes of wheat kernels.  Considered together, this crowd of tillers is called the stool.  They not only help support the plant, they are complete wheat plants, capable of doubling or tripling the overall yield.

Glenn Hard Red Spring Wheat 14 days after sowing in Agoura Hills

All this action emerges from one wheat seed, or berry.  I admire the fecund and complex nature of the modern hexaploid wheat species, with three times as many chromosomes as the earliest wheat-like grasses.  Thought to have been under cultivation for 9,000 years, the small grain called wheat has evolved into tens of thousands of natural varieties and cultivars.  Varieties are successful in a wide variety of climates: hot/cold; wet/dry; low & high altitudes.  And now we’re looking to see how certain cultivars do near our City of Angels, just off the 101 in Agoura Hills.

Sonora Soft White Winter Wheat 30 days after sowing.
For our crops, sowed in Late November and mid December, I was thinking that tillers will only begin appearing some 60 days after sowing, about when the fourth leaf appears on the main stem.  The Sonora plants that I unearthed on December 28th had three leaves and no obvious tillers, although I know that us city dwellers are likely to have trouble telling the difference between tillers and leaves.  Looking at web sites on tillers and tillering (both a noun and verb form) I found this image of wheat at the fifth leaf stage.

Leaves and tillers looked pretty straight forward, but my eye went to that Coleoptile Tiller.  Here’s what I read about growth stages.   “Each tiller (like each leaf)  is numbered when it becomes visible. There are two types of tillers: those arising from a crown leaf axis and those arising from the coleoptile node. When present there will only be one coleoptile tiller. The plant in the drawing has two tillers and a coleoptile tiller.”

I’d read that the first shoot that emerges from the germinating seed is encased in a coleoptile sheath that protects the shoot, burrowing an easier pathway upward from the seed to the soil surface.  And now I see that one tiller benefits from the same protective sheathing.  Another kind of redundancy.  A study group in Australia is currently researching the benefits of a larger, faster growing coleoptile tiller.  They hope to find out whether it increases plant leaf area and biomass, while playing a role in improved water use (cutting down on ground surface evaporation) and helping reduce competition from weeds.  This is apparently an area of research that hasn’t been pursued in depth.

I took another look at the Sonora plants I’d uprooted.  Almost all of these 3-leafed plants show what appear to be tillers – I’d thought they were secondary stems -- emerging from near where the first stem had grown out of the seed.  In the photo, the now-empty coleoptile sheath is visible on the main stem (at the bottom) and on the coleoptile tiller (at the top).

Indeed our Sonora has coleoptile tillers!  And they were likely to have been just at the soil surface in late December.  My thought is we might really see tillering in progress early in February.  After that, we get stem extension and those plants will soon be knee high.  Or higher.

I'll try to avoid using the term coleoptile in subsequent posts.

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