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3. Triticale (Triticum and Secale)

The first man-made cereal. It exists in several ploidy levels. The hexaploid and octoploid triticales have recieved the greatest amount of breeding effort. 

Hexaploid triticale (primary) is obtained after doubling the chromosomes of the F1 hybrid between tetraploid wheat (AABB) and diploid rye (RR). The triploid F1 hybrid by itself would not be fertile. At meiosis, chromosomes would have no homologues with which to pair. Doubling the chromosomes results in normal meioses, since all chromosomes can now pair.

The genome formula for hexaploid triticale is 2n = 6x = 42 and its genome composition is AABBRR.

Octoploid triticale (secondary) was obtained by crossing hexaploid wheat (AABBDD) to rye. The genome formula for octoploid triticale is 2n=8x=56 and its genome composition is AABBDDRR.

Problems with hybrids included cytogenetic instability, reduced seed set and shrivelled seed which were major constraints for successful productivity. The cytological instability was attributed to cytoplasmic effects, differences between duration of meiosis and DNA content of wheat and rye, and interaction between wheat and rye chromosomes. 

In octoploid triticale, a lower degree of aneuploidy, more stable meiosis, higher fertility than hexaploid triticale. They are characterized by good winter hardiness, high protein content,good baking quality, early flowering, seed maturity and large seed size. However, seed sterility, disease (eg. ergot) and early sprouting are still probelmatic.

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previous  page PLNT3140 Introductory Cytogenetics 
Lecture 21, part 4 of 4
first page