RFLPs push BC2 selections ahead

--Ed Weck, Mary Bergstedt, David Farrar, Mike Kiefer, Carolynn Krumm, Mike Lundell, Doug Mead, Hope Sunderland, Roger Taylor and Carol Ann Wangen

RFLP-assisted selection for recurrent parent alleles should increase the generational gain over phenotypic selection in backcross breeding. Computer simulations suggest that the recurrent parent genotype can be reconstructed in three generations of 30 individuals each (Tanksley et al. Bio/Technology 7:257, 1989). Here we compare RFLP-assisted selection of BC2 progeny with theoretical estimates of BC2 (backcross 2) and BC3 population means in the absence of selection.

A BC1 population of 125 plants was planted in the greenhouse and analyzed with probes for the single gene of interest. The 57 plants heterozygous for the trait were analyzed with up to 38 RFLP probes to estimate percentage recurrent parent. These 57 plants were backcrossed to the recurrent parent to create BC2 ears. BC2 seed (100) of the three BC1 plants with the highest percentage recurrent parent (plants 24, 95, and 38) were planted in the field. BC2 plants (58) heterozygous for the trait of interest were analyzed with probes heterozygous (non recurrent parent) in the BC1. Concurrent with the laboratory analysis the BC2 plants were backcrossed to create BC3 plants.

The recurrent parent allele number distribution for 57 BC1 plants is shown in solid bars in Figure 1. The three BC1 plants selected for further backcrossing (24,95, and 38) and the BC2 plants derived therefrom are shown, respectively, in: white bars; diagonal bars; and horizontal bars. The population mean of the RFLP-selected BC2 plants (32) is closer to the theoretical mean for a BC3 population (33.25) than a BC2 population (28.5). The attainment of 97.4% recurrent parent (37/38 probes; 58 plants) after two backcross generations suggests that two RFLP-assisted backcrosses may be sufficient to return an inbred to type.

Figure 1.  RFLP-selected BC2 Population.

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