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.
|
|
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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