Use of ig mutation for cms counterparts of corn lines

In 1972 the ig mutation stimulating the occurrence of androgenic haploids was obtained from Maize Genetics Cooperation. We tried to find out possible ways of use of this mutation in corn breeding. Dr. J. L. Kermicle (Science, 1969, 166: 1422-1424), who discovered it, reported that its presence in a female parent results in the occurrence of androgenic haploids up to 3% frequency. In our six-year experiments the average frequency of androgenesis due to ig mutation was about 0.03%. However, in some ears it reached 1.5%. Such pleiotropic effects of the ig gene as a lack of some kernels in ear and small size kernels, somewhat hamper the isolation of haploids through the A C R-nj marker system. Therefore, it proves expedient to use matroclinical haploids for the development of homozygous lines.

Mutation ig may successfully be used for the transfer of lines to cms by androgenesis. To realize this use ig and A C R-nj genes were incorporated into individuals with C, S and T types of cms. Some androgenic haploids were obtained from more than 20 lines carrying cytoplasms of N, C, S and T types. The sterile counterparts of V35, B59, N8, WF9 and other lines were developed by this method.

Table. Spontaneous female fertility of androgenic haploids pollinated with the pollen of the original lines
 
Source of androgenic haploids Number of pollinated haploid plants Number of kernels set per ear X ± SX
Va35 6 31 ± 7.2
N8 8 27 ± 6.3
B59 6 18 ± 6.5
WF9 37 42 ± 10.1
W64 17 33 ± 4.1
W155 8 8 ± 2.7

As natural female fertility in haploids is high (Table) the artificial diploidization of androgenic haploids with colchicine for the transfer of the lines to a sterile base is not needed. From more than 200 pollinated androgenic plants only nine plants did not set kernels. It should be noted that the best seed set in haploids is obtained when pollination is 5-10 days later.

Thus, the ig mutation may be used for the development of sterile counterparts of lines and for various genetic studies dealing with determination of the importance of the cytoplasm.

M. V. Chumak


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