FEATURE ATTRACTION AND HYBRID VIGOR

In a message dated 97-01-18 18:14:13 EST, you write:

<< Some very important breeding lines are highly inbred for five and six
 > generations to arrive at the desired goal. Introductions from such lines
 > should be grown several years for evaluation of hardiness and freedom from
 > conditions such as bloom-out before they are used in the breeding program.
 > 
 > Fred Kerr, Rainbow Acres, Region 14, USDA zone 9. 
 >  >>

Heterosis, or hybrid vigor, is diminished by intensive line breeding.  As
some of you will know, I have written a couple of articles for the Reblooming
Iris Recorder suggesting that the origin of rebloom may be heterosis.  Two
documented cases in which reblooming lines have been created are: 1) the
lines behind BABY BLESSED, which have wide crosses involving I. pumilla and
tall bearded irises and 2) the work that Dr. Nearpass has done to develop
tetraploid MTB's which has involved crossing I. aphylla with TB's.  

Fred Kerr's comment about intensive line breeding of irises diminishing vigor
set me to thinking.  That conclusion is consistent with what is known about
heterosis.  The hybrid vigor often gained by crossing different species is
diminished in each generation if the hybrid is selfed.  The selfing which is
done to get newer and bolder color or lace or ruffles, is also likely to
reduce vigor.  From a breeder's perspective, that selfing is useful to obtain
distinctive offspring.  If the loss of vigor is recognized, the logical next
step, to get good garden irises, is to bring into the breeding program irises
with different genetic heritage.   

The only cold weather reblooming iris that I am aware of that has come from
intense line breeding is Dave Niswonger's LATE LILAC.  It is an anomaly, but
it's unique heritage does not invalidate the proved depletion of heterosis
resulting from intense line breeding.  

In cold, wet climate areas, the irises that are heavily line bred are even
greater problems when the genetic background includes heavy doses of I.
mesoptamica or I. cypriana.  These irises apparently can withstand the cold
but not in combination with heavy soils and lots of moisure.  

I personally think that Fred Kerr's iris breeding principles are consistent
with getting better garden irises for wide geographic adaptability. (And I
purchased a number of his irises last year because of this, and because they
are very beautiful!)  Clarence Mahan in VA
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