In previous MNL items (1974, 1975) we have described the use of alien addition monosomes and disomes for Tr7 (Tripsacum chromosome 7) on a sugary-shrunken-2 background in order to allow seed production of the double recessive (su sh2) by the temporary masking of su with its Su allele on Tr7. The low transmission rate of the alien monosome for Tr7 results in the expression of the desirable double recessive in most of the progeny crop ears. Ordinarily, seed production of su sh2 is nearly impossible because of its low germination rate (about 10%).
A new example of this genetic technique involves seed production of the triple recessive su sh wx. Tr5 (Tripsacum chromosome 5) is the alien maintainer. As a homeolog to maize chromosome 9, it not only carries the dominant Sh Wx alleles, but also the dominant C allele controlling aleurone color. All three of these dominants are important to the Tr5 system. Although the alien addition disome for Tr5 is largely male sterile, the monosomic condition is fully fertile. The monosomic inbred su, c sh wx, Tr5(1), with the undesirable low germination masked by Tr5, may be crossed with a standard sweet corn of the genotype su, c Sh Wx. The purple kernels (representing the transmission of Tr5 with its dominant C allele) scattered on each ear in the progeny of the cross may be removed by a Sortex* or other electric sorting machine. Thus, the triple recessive su sh wx is completely unmasked and segregates on the crop ear in the expected ratio when the remaining (non-purple) seed is planted.
Walton C. Galinat
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