Genetics of cms-C fertility restoration

Some preliminary results of studies of fertility restoration of several C type cytoplasms were reported last year (Kheyr-Pour et al., MNL 53:48-51). Additional data from a systematic series of crosses, backcrosses and selfs this year substantiate our contention that fertility restoration of the C, Bb, ES, PR and RB cytoplasms is controlled by no more than 2 co-dominant genes in the lines that we have studied. We did not find any evidence for the involvement of 3 or more restorer factors in C restoration as has been reported previously by Josephson et al. (Proc. 33rd Ann. Corn & Sorghum Res. Conf.:48-59, 1978) for a somewhat different group of inbred lines. In fact, in most lines we studied, only one restorer gene is apparent, but some data suggest that, at least for a few lines, a second gene may be involved.

In our studies, most inbreds segregated for a single restorer gene (Table 1). Progeny of single crosses between lines that were presumably of rf* rf* and Rf* rf* genotypes gave approximately 1:1 segregation ratios in Aurora, N.Y. (1979) and in Homestead, Fla. (1978-79 and 1979-80 winter nurseries). Numerous self progenies of theoretically heterozygous plants, produced by crossing NY821LERf onto several C sterile plants, when crossed onto a C sterile tester gave a segregation ratio of 3 fertile to 1 sterile. This, again, indicated that a single restorer gene was segregating in the lines tested.

Table 1. Fertility restoration reaction of C group cytoplasms in crosses involving C rfrf X C Rfrf genotypes.
  Heterozygous restorer lines (C Rfrf)
  W182BN x A619) (W182BN x NY821 LERf) (W64A x W182BN)( R181B x A619) (NYD410 x NY821 LERf)
Sterile versions (C rfrf) S :Pf :F S :PF :F S :PF :F S :PF :F S :PF :F
C x W182BN 26 :4 :43 102 :6 :99 62 :5 :57 34 :14 :54 83 :15 :114
Bb x " 40 :5 :48 14 :2 :8 27 :1 :36 - -
ES x " 68 :5 :61 80 :5 :83 35 :2 :53 - -
PR x " 40 :4 :36 78 :7 :59 52 :5 :33 - -
RB x " 47 :8 :45 41 :8 :38 57 :20 :38 - -
C x Co107 61 :4 :62 55 :9 :67 365 :17 :327 59 :6 :53 5 :0 :4
Bb x " 62 :7 :70 113 :1 :87 100 :4 : 87 - -
ES x " 65 :2 :65 70 :0 :63 394 :7 :249 - -
PR x " 66 :4 :72 62 :1 :57 295 :9 :261 - -

aAll progenies were rated on 1-5 scale (1=sterile, 5=fully fertile) in Florida winter 1978-79, 1979-80, and Aurora, summer 1979 nurseries.

bMost of the partially fertile plants (PF=ratings of 3 and 4) exhibit a "late breaking" of sterility.

A preliminary series of crosses between several different lines that were C sterile and had shown single gene segregation when crossed with restorer lines failed to give any fully fertile progeny suggesting that these 7 inbreds tested do not possess complementary restorer genes (Table 2). There were some partially fertile progeny which typically exhibited a delayed breaking of pollen which occurred about 5-10 days post-silking. However, an additional series of crosses involving dent inbreds A498, NYD410, NY254, NY306, NY317, NY453, Oh480 and W37A crossed onto sterile PR or C cytoplasm versions of sweet corn lines Pf41 and Me2Rt did suggest the presence of an additional restorer gene. Several of these lines restored the Me2Rt cytoplasms but did not restore the Pf41 cytoplasms. The ability of these dent inbreds to restore the C cytoplasms in the Me2Rt background only suggests that they possess a restorer gene that complements with another gene present in the Me2Rt background but lacking in the Pf41 background. Additional tests are underway to determine whether or not two complementary genes are involved in C fertility restoration for these and certain other lines.

Table 2. Fertility restoration reactions of C group cytoplasms in crosses involving C rfrf x C rfrf genotypes.
  (NYD410 x Oh51A) W182BN
Sterile inbreds S :PF :F S :PF :F
W182BN-C 99 :5 :0 90 :0 :0
Co107-C 136 :7 :0 92 :0 :0
NYD410-C   92 :0 :0
Oh51A-C   90 :0 :0
R181B-C   93 :0 :0
A636-RE   88 :0 :0
SD10-RB   62 :23 :0

aAll progenies were rated on 1-5 scale (1=sterile, 5=fully fertile) in Florida winter 1978-79, 1979-80, and Aurora, summer 1979 nurseries.

bMost of the partially fertile plants (PF=ratings of 3 and 4) exhibit a "late breaking" of sterility.

The selection of A632-PR cytoplasm types that do not exhibit a late break of pollen fertility was continued. Last summer at Aurora, N.Y. ears selected for low levels of late breaking in the 1978-79 Florida generation produced rows with from 0-14 plants (out of 24) showing late breaking while non-selected ears produced rows with from 18-20 plants that showed late breaking of pollen. In the 1979-80 Florida generation, all of the progeny of non-late breaking plants from the 1979 summer nursery were completely sterile. None of the plants exhibited a late break. Whether this complete sterility will continue to hold in other environmental regimes is not known, but the results are promising. The data suggest that the late breaking of fertility in lines such as A632 which lack a major restorer gene may be influenced by several modifier genes as well as environmental conditions.

A. Kheyr-Pour and V. E. Gracen

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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