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Colby, Kansas | In another thread on here NEMOScott asked if breeding hybrid sorghum seed was the same as corn. We'll this has been good for me as it's been about 1 1/2 years since my breeding class, so back to the notes I went, probably learned more this time than the first. I wish I could have gotten the textbook drawings in, but you'll have to settle for my recreations. It is very likely somebody on this board knows more about breeding than I, feel free to correct any errors.
The first figure shows typical corn breeding, I would imagine most here are familiar with that. There are also various modifications of that, one such is a modified single cross where you cross 2 Inbred A's from the same genetic family by detasseling the one then the seed from that is grown and crossed with Inbred B to get your F1 Hybrid Seed. The aforementioned can also be done with three completely unrelated inbreds to form a three-way cross.
Sorghum is somewhat different as a technique called CMS (cytoplasmic male sterility) is used. In the diagram, A-lines and B-lines are basically the same genotype but the A-line is male sterile, the B-line male fertile. Any sorghum breeding line that cannot restore fertility is not capable of being a R-line and becomes a B-line. B-lines are continually backcrossed until they become male-sterile at which time they are now an A-line. So basically your parental lines are the A-line and the R-line. The seed produced from that cross is your hybrid sorghum seed.
In production, B-lines and R-lines are maintained by bagging the heads, thus forcing self pollination. A-lines are increased in isolation by crossing A-lines by B-lines. The A x R hybrid is produced by planting blocks of rows of A- and R-lines. Typically 12 rows of A-line next to 4 rows or R-line.
Its interesting to note that the CMS method was also used in corn from the 1950's until 1970. There was only one genetic source being used to provide the male sterility. In 1970 a blight disease to which this genetic was susceptible swept though the corn belt. Over 90% of the hybrids being grown were using this susceptible source. I would imagine many folks on this board know much more about this than I.
If you have made it to this point and are still awake kudos to you. Hopefully you learned something today, I know I did by relearning it, thanks for asking the question Scott.
Lucas
 (TypicalCornBreeding.JPG)
 (TypicalSorghumBreeding.JPG)
Attachments
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 TypicalCornBreeding.JPG (20KB - 124 downloads)
TypicalSorghumBreeding.JPG (30KB - 124 downloads)
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How Breeding Corn and Sorghum Differs - for NEMOScott and anyone else
