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REB: HYB:question - inheritance of higher temperature triggers
iris@hort.net
  • Subject: REB: HYB:question - inheritance of higher temperature triggers
  • From: Linda Mann <101l@rewrite.hort.net>
  • Date: Fri, 24 Oct 2014 06:22:56 -0400

What to do next spring....

With record lows several times during the summer this year, and very late (still not here yet) killing freeze, I may be seeing seedlings bloom this fall that I'll rarely see rebloom again. ~75 different seedlings from ~30 different crosses either bloomed, blooming, or with stalks up starting in Aug this year.

I've been thinking about the upper and lower temperature ranges that these rebloomers need in order to rebloom, wondering how to maximize chances of breeding reliable late summer/early fall rebloomers for my growing conditions.

Chuck in Canada, zone 4, I think, has talked about his records that show his rebloomers (like Immortality) need a certain number of growing degree days <above> a certain threshold temperature in order to mature enough to be able to put up a bloomstalk.

I'm in east TN, zone 7, approaching zone 8, and most of the irises that reliably rebloom here seem to need at least a few nights below 60 to trigger stalk formation. I have such a long growing season, that maturity isn't the issue here that it is for Chuck (assuming it rains). Because of normally very high humidity at night here, nighttime lows are high in summer compared to lows in low humidity (Mediterranean type) regions.

My question is, how might this upper 'cool temperature' trigger mechanism work? Would the tolerance for a warmer summer trigger be an on/off switch or ?

I have found only 2 cultivars that reliably put up bloomstalks without some cool summer temperatures - Belvi Queen and Tea Leaves. There are probably more, but these are the only two I've grown here that tolerate the disease burden of my growing conditions <and> can put up stalks in the heat of summer. Imm occasionally does rebloom in mid summer, but isn't anywhere near as reliable as Belvi Queen.

So might this be one 'broken' gene, that allows maturation at higher temperatures and it's just so uncommon in combination with disease resistance that it's very rare in my population of plants? Or is it some kind of broken gene that allows a hormonal trigger for initiating stalk production at higher temperatures? & how would that work?

Or is it more likely to be a combination of growth/disease resistance genes that just allow the plant to reach maturity when it's hot and humid?

I have gotten hot weather (August) rebloom from Tea Leaves as both pod and pollen parent, but none that have ever bloomed in mid summer like Tea Leaves has (rarely) done.

I keep trying, but have had no luck getting seeds either way from Belvi Queen. One batch of seedlnigs from Margie with BQ as pod have also refused to be fertile so far.

Lots of reblooming seedlings to work with next spring, just not sure which are most likely to produce Aug/Sept blooming children. Only one has rebloomed earlier than Aug - one stalk in late July from one of the Immortality X (Final Episode x (Tea Leaves x Matrix)) seedlings. It also bloomed in August and is blooming now.

Linda Mann east TN USA zone 7b

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