1. Inbreeding depression and non‑allelic gene interaction.


Material representing five levels of inbreeding was developed from two populations of prolific corn. The genetic representation of the material and their relative percentage of heterozygosity are as follows:


Per cent Heterozygosity             Material

0                                   Longtime inbred lines, P1 and P2

100                                 F1

50                                  F2


                                    (1) B1 =  F1 x P1

                                    (2) B2 = F1 x P2


75                                  Double backcrosses

                                    (1) B12 = (F1 x P1) x P2

                                    (2) B21 = (F1 x P2) x P1

25                                  Double backcrosses

                                    (1) B11 = (F1 x P1) x P1

                                    (2) B22 = (F1 x P2) x P2


The various levels of heterozygosity were developed from the two populations, CI21‑NC7 and NC16‑NC18. Twenty‑five replications containing one plot of each of the following: P1, P2, B1, B2, B12, B21, B11, B22 and two plots of F1 and F2 were grown in 1948. The data for eight characters were analyzed to determine the presence of non‑allelic gene interactions, the presence of which would result in non‑linear relationships between performance and per cent heterozygosity.


Many non‑linear relationships were found to exist but could have been partially explained by the particular environmental conditions under which the test was grown. Material is available for testing again in 1950, at which time several locations and different planting dates will be used to provide more information concerning genotype-environmental interactions.


H. F. Robinson