Sunday, September 2, 2012

Dreaming Pink Siberians

By Bob Hollingworth

Clear pink is a color we do not much associate with Siberians. There is white, blue, violet, lavender, red-violet, purple and now red/yellow blends, but not really a true pink. Pink is the poor relative as a color. Pink in irises can come from one of two sources, either from carotenoid (yellow, orange and pink) pigments or anthocyanins (blue, red, lavender and violet colors). Bearded irises have both types, and so clear pinks are not uncommon – think 'Beverly Sills' for instance. But, so far, there is no evidence for a carotenoid pink in Siberians (or other beardless irises to the best of my limited knowledge). So pink has to come through the anthocyanins, and of course this can give pinkish Siberians, but always with a bluish cast (lavender-pink, orchid-pink) – e.g. 'Pink Haze' (McGarvey, 1980) or 'Mary Louis Michie' (AM Miller, 1995). The fact that there has been little advance in achieving clearer pinks in Siberians in many years suggests that this is not necessarily an easy field to cultivate, but for that reason it is tempting as well as challenging.
'Pink Haze'

As with so many other things, working in this area came to my mind as an afterthought a few years ago when a batch of seedlings seemed to give some marginal improvement in “pinkness”. These still tend to the blue side of pink, but truly I think could be termed peppermint pink. One (09F3A3) is under evaluation for introduction. Perhaps line breeding can slowly improve these further, but I have a few other thoughts about where cleaner and richer pinks might come from.
The pinkest Siberian I ever remember seeing was Pink Haze growing in a far part of our garden in Indiana years ago. It was almost flamingo pink and seemed quite different from the usual color, so I checked the soil pH. For some reason it was 7.5, about the upper limit for Siberians to grow. Maybe that could explain the unusual color shift. So this brings us to the first thought. The color of anthocyanin pigments is quite complex and can be greatly altered by soil pH. Just think how the color of hydrangeas can be changed from pink to blue by adding aluminum salts to the soil. The pigment is the same but when it is complexed with aluminum, it changes from pink to blue. And, to make a hydrangea pinker, increasing soil pH helps, since this limits the uptake of aluminum. Could this be an explanation why Pink Haze looked so pink growing at an unusually high pH?  I guess we’ll never know for certain, but certainly the soil pH can greatly affect flower color. Which raises another question - are pink Siberians pinker here in the Midwest (with generally neutral soils) than on the east or west coasts (often quite acid soils)? A study of the effect of soil pH on Siberian flower color would be an interesting thing to try.

Just as external pH changes these colors, so does the pH inside the cell (which is not directly affected by soil pH). Also, different metals and the interaction with other co-pigment molecules can change color in a complex way that goes well beyond the bounds of this blog. Subtle change in cell pH (as small as 0.1 unit) can cause a surprisingly large change in the blue-pink color balance of flowers. Several tactics could work in theory to take advantage of this to give purer pinks - increased cell acidity, greater uptake of metals (aluminum) etc., but there is no obvious way to control these as a hybridizer, so you can only make promising crosses and hope for a lucky break in seedlings. Perhaps this is not just a pipe dream. There are quite clear pink Japanese irises with similar pigments to those in the Siberians.
I’m hoping that we saw such a break this year with one seedling (10J4A5). This stood out quite strongly in a group of new seedlings as a stronger, clearer deep pink than the others. One year does not a breakthrough make, so we will need to see this bloom again to be sure it wasn’t just a weird aberration in what has been a very weird and nasty growing year, but that’s what makes hybridizing so addictive.

'Fancy This'
The other means to brighter, pinker pinks is to play a subtle game of combining the current lavender pinks with a light yellow underlay. Too much yellow makes brownish shades that can be interesting but are not the objective.

I think this effect may be what lies behind two recent introductions from Jan Sacks and Marty Schafer, 'Fiona' (2010) and, particularly, 'Fancy This' (2012). To my eye these have a distinctly richer
pink color than previous Siberians. Even more exciting is the thought that if you can get purer pinks with less blue influence through mechanism 1 and then combine this with yellow in mechanism 2, you could head towards true orange. Dreams, dreams.

1 comment:

  1. I believe they will get there. With your work, and the work of other fine hybridizers, there is little that won't be accomplished.


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