Illinois State University

A study of the progeny of monosomic-4 plants in maize
--N. I. Teissonniere, D. F. Weber and M. C. Schneerman

We have explored a limited number of progeny of monosomic-4 maize plants. Monosomic-4 plants were produced utilizing the r-x1 system as described by Weber (Maize Handbook, M. Freeling and V. Walbot, eds., pp 350-358, 1993). Monosomic-4 plants were selected and crossed as male parents to the inbred B73. The monosomic-4 plants had su on their single chromosome 4 and B73 was Su/Su; thus, the F1s were Su/su.

F1s from the above cross were reciprocally testcrossed, and the number of non-sugary (Su/su) and sugary (su/su) kernels were determined. Forty-nine F1s were testcrossed as female parents, and none of these had ratios that were significantly different from a 1:1 ratio of non-sugary to sugary kernels. However, 15 of 49 F1s testcrossed as male parents had ratios that deviated significantly from a 1:1 ratio as shown in the table. Thirteen had more sugary than non-sugary kernels and 2 had fewer sugary than non-sugary kernels.
Plant #
Non-sugary#  Sugary X2
245-3 149 115 4.38
247-9 217 170 5.71
246-7 88 119 4.64
254-5 0 16 16
246-3 9 428 428
247-6 114 168 10.3
252-11 130 172 5.84
246-6 148 192 5.69
246-5 114 165 9.32
253-6 90 124 5.40
253-3 63 146 33.0
246-3 1 285 282
246-11 177 239 9.24
252-7 108 141 4.37

The reason for these deviations from a 1:1 ratio is not known. In wheat, univalent chromosomes frequently misdivide producing telocentric chromosomes (Sears, Chromosoma 4:535-550, 1952). If the univalent chromosome 4 in the monosomic-4 plant underwent misdivision to produce telocentrics for both arms of chromosome 4, the F1s would have a normal chromosome 4 with Su and a telocentric for 4S with su. It is possible that the telocentric would demonstrate reduced transmission, and if such an individual were testcrossed, less than half non-sugary kernels would be produced. Two of the plants demonstrated reduced transmission of su when they were testcrossed as male parents; however, neither of these demonstrate reduced transmission when testcrossed as female parents. We believe it is unlikely that these plants contain telocentrics for chromosome 4. 

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