Re: Stability of tetraploid Siberians

Jim -- After 25 years of doing this, I can say that you're dead on regarding induced tetraploidy in Siberians in pretty much every detail. Once you make the cross of converted x full tetraploid, the progeny are as close to 100% stable tets as I can determine. Fully converted plants (germinating seedling treatment with colchicine in particular) are much more often mixed diploid/tetraploid than purely tetraploid in their pollen characteristics, but apparently full induced tetraploids aren't so uncommon (10-20% is my guess). That figure probably depends on how hard you hit them with colchicine (and whether a few smaller pollen grains that always seem to be there really count as diploid). Incidentally, for anyone interested, I tried some new spindle-inhibiting herbicides, oryzalin (a treflan analog) and diphenamid, a couple of years ago as  tetraploidy-inducing agents and a scattering of results from first flowerings this year indicated that oryzalin was working well and maybe very well. We'll know better about these two next year. Treflan itself never did much for me. Bob Hollingworth



Murphy <murphy@cstone.net> wrote:

>Hi Jeff, and Robins,
> I have lots of experience with Tet germplasm in daylilies and a few other
>perennials.
> I believe that the following holds true, as a general rule, for all
>perennials.
> Any plant that has been induced to be tet with colchicine, orazylin, or
>naturally occurring has a large chance of having both dip and tet pollen. The
>exception would be full conversions, which are not too common, but very
>possible. Full conversions are those that all cells in the plant have been
>converted to tet. Many times these will be both pod and pollen fertile.
> More than 90% of all conversions have both dip and tet pollen, plus, broken
>pollen, and will be very difficult to set pods on.
>  The big, good news, is that if you place tet pollen from a conversion on a
>tet derived by sexual means, and cap the cross to prevent insect crosses,
>that the progeny will be full tet in almost 100% of the cases. Where one sets
>pollen on converted tets, the outcome is iffy and must be ascertained by
>microscopy.
> Almost all tet pollen is 40% bigger than dip pollen- in my experience. If
>you look thru a microscope with a measuring reticle at converted pollen, you
>will usually see a range of sizes. This means that the conversion is not a
>full conversion. These conversions will sometimes revert to dip and sometimes
>remain stable. There is usually lots of broken pollen in a conversion too.
>This pollen is non viable.
> As a general rule of thumb, always use the converted parent as a pollen
>parent to ensure tet progeny. If you use the converted parent as a pod
>parent, you can not be sure that the conversion and subsequent progeny will
>be fully tet, and they might be dip. You would not find this out for two
>years, in those without laboratory resources.
> As to different numbers of chromosome counts, it is very tough to make
>crosses if the counts do not match up. The father of modern daylilies, Arlo B
>Stout, made tens of thousands of crosses between Hemerocallis Fulva, a
>triploid, and other diploid species to generate a handful of viable seed.
>Crossing triploids is very difficult, even if the numbers match.
> Perhaps Marty and Jan, or someone with lots of Iris experience could comment
>further and correct me! Jim
>
>dunlopjj wrote:
>
>> Greetings to all.  Recently I've been thinking about the stability
>> of tetraploid germplasm in Siberians.  My considered opinion is that
>> even converted material (P1) used with stable tets, should produce
>> stable tet pollen and pods in the P2 generation and beyond.  Assuming
>> of course, the P1 cross took as tetraploid without reversion
>> (reversion giving no seeds or nonviable seeds), or without altering
>> the P1 cross progeny to another state of ploidy (to triploid,
>> octoploid, etc).  Can we count on tetraploids in the P2, P3 and
>> higher being very stable?  Also does anyone have a grip on
>> statistical probabilities of reversion or alteration in ploidy level
>> in the P2 or beyond?  Thanks for your help.
>>
>> Jeff Dunlop
>>
>> To post to Sibrob: sibrob@yahoogroups.com
>>
>> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>


-- 
Bob and Judy Hollingworth



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