Identification of a recessive semi-dwarf mutation
--Olsen, MS, Phillips, RL

We have identified a recessive semi-dwarf occurring as a spontaneous mutation in the Mo17 genetic background. These plants are approximately half as tall as normal Mo17 plants but have the same number of nodes. Semi-dwarf plants have erect leaves and tassel branches and exhibit a significant silk delay.

Semi-dwarf plants were used as male parents in crosses with normal sibs as well as wild-type Mo17 and B73 plants. Additionally, four normal sibs were self-pollinated in order to progeny-test the heterozygous class. In crosses with wild-type Mo17 and B73 plants, no semi-dwarf plants were recovered among 60 F1 progeny of each cross. Two of the four self-pollinated sibs were homozygous wild-type and did not show segregation. Progeny of the remaining two self-pollinated sibs exhibited 3 wild-type : 1 semi-dwarf segregation (Table 1). Two test-crosses of semi-dwarf plants with heterozygous sibs segregated 1 wild-type : 1 semi-dwarf (Table 2).

Although complementation tests with known semi-dwarf mutants have not been performed, both sdw1 and sdw2 exhibit dominant behavior (Neuffer, M.G., E.H. Coe, S.R. Wessler, Mutants of Maize, p 283, 1997).

Table 1. Segregation ratios of self-pollinated heterozygous plants.
 
 
Progeny classes
     
Plant Wild-type Semi-dwarf Ratio tested c2 P
1 20 3 3:1 1.754 0.185
2 20 9 3:1 0.563 0.453
Combined 40 12 3:1 0.103 0.748

Table 2. Segregation ratios of homozygous semi-dwarf x heterozygote test-crosses.
 
 
Progeny classes
     
Plant Wild-type Semi-dwarf Ratio tested c2 P
1 30 27 1:1 0.158 0.691
2 27 24 1:1 0.176 0.675
Combined 57 51 1:1 0.333 0.563


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