Why are there tall plants in my semi-dwarf wheat?

If the differences in height are sporadic throughout the field, i.e. the odd plant here and there, it is probably one of three things causing these ‘tall-types’:

  1. a result if seed of another variety was inadvertently comingled with the variety you think you have (through cleaning of equipment, bins, harvest, etc.).
  2. a variety that is segregating for plant height – is less common but in extreme growing conditions can bring differences in plant height that previously had gone unnoticed.
  3. with introduction of semi-dwarf genes (Rht1), it’s been noticed that in certain lines and genetic backgrounds a number of tall plants would appear at a low frequency from one generation to the next generation.  Fancy terms is some plants become aneuploids, meaning individual progeny has one or more chromosome missing or extra.  Monosomic deletions, i.e. plants missing one chromosome, are most commonly encountered. Because Rht1 act as a suppressor of height, their reduced dosage as in monosomics, produces plants taller than in the euploid condition.If seed is saved, half the plants derived from these tall-types should revert back to the original variety, while the other half of the plants will be the taller-types again.

There is a very good article in the Saskatchewan Seed Guide last year (page 20) further explaining these ‘tall types’ in semi-dwarf wheat: http://www.saskseed.ca/images/seed_guide2015.pdf.

Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture


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