It was noted that some En-containing populations in our regular nursery plots generated mutants at notable frequencies. During the seasons between 1990 greenhouse and 1992 summer, at least 24 mutant plants were noted. The 24 mutants can be traced back to at least 5 independent origins. The number and phenotypes of the mutants and the populations in which the mutants originated are listed in Table 1. The population size included from the '92 summer nursery back through '89 summer, to which the farthest mutant is traced.
Table 1. Mutants obtained from several En-containing populations.
913834 and 924602 can be traced back to a common parent in one generation,
while 922018, 922020 and 922021 can be traced back to a common parent in
two generations. All striped mutants are considered to be 2 in calculation
of mutation rates, since they have two independent origins. The 3 mutants
in the last row were considered as one.
| Entry | Genotype | Pop' n size | Mutant | Mut. rate |
| 913834 | T2-3d~a-m(papu)
/a et x Ht B37 or @ |
510 | 5 striped | 3.92 x 10-3 |
| 924602 | 3 striped | |||
| 922018 | 6 striped | |||
| 922020 | 2 striped | |||
| 922021 | 2 striped | |||
| 922036-1 | T2-3e~a-m(papu)/a sh @ | 214 | 1 silky tasseled | 4.67 x 10-3 |
| 922350 | T4-6(033-16)~c2-m1/"
x Normal or @ |
720 | 1 dwarf | 1.39 x 10-3 |
| 924832, 33 | T7-9(027-9) ~wx-844/
c sh wx @ |
343 | 3 dwarfs | 2.92 x 10-3 |
All mutant phenotypes are heritable and independent of En activity and independent of the translocation feature. The striped-leaf mutants are being investigated using reciprocal crosses to verify whether they were generated by deficiencies as the mutants isolated by Robertson and Stinard (Genetics 115:353-361, 1987). The silky tassel mutant is reported in an accompanying report (this issue). All the dwarf mutants grow between 50 and 70 cm tall. Their leaves were compacted together, and their pollen and ears were severely affected so that no seed was obtained from crosses in both ways.
The mechanisms by which En enhances the generation of mutants are not clear, though Robertson and Stinard (Genetics 115:353-361, 1987) proposed several for the high mutation rates associated with their Mutator populations.
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