Cytological evidence of terminal deficiencies produced by the r-X1 deletion in maize

Abstract

In addition to monosomes and trisomes, the r-X1 deletion generates chromosome deficiencies of parts of an arm; these deficiencies now have been identified cytologically. Of eight japonica plants produced from the cross of r-X1/R-r as female with the Mangelsdorf's tester, five were complete and three were partial monosomes. The isolated partial monosomes had chromosome breaks in the region between the centromere and the japonica locus. Their breakpoints were at the 0.33, 0.30, and 0.25 positions, respectively, on the long arm of chromosome 8. Additionally, a liguleless plant produced from the same cross carried a partial monosome with a breakpoint at the 0.09 position on the short arm of chromosome 2. Although partial monosomes associated with other chromosome arms have not been investigated, it is evident that the action of the r-X1 deletion is not restricted to the centromeric region of maize chromosomes. Key words: maize, r-X1 deletion, terminal deficiencies, monosomes.