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Effect of a Generation of Inbreeding on Genetic Variation in Corn (Zea mays L.) as Related to Recurrent Selection Procedures¹

Response from selection for combining ability is proportional to the genetic variance among test crosses in each cycle. Theoretically, this variance can be increased appreciably by a generation of inbreeding in the population under selection prior to initiation of a new cycle. for a single locus with two alleles, crossing S₁ rather than S₀ plants with a tester is expected to increase variance among test crosses within intercross progenies (of selected S₁ lines from the previous cycle) by 100%, and over the entire population by 50%. Sib-pollination within intercross progenies would be only one-half as effective as selfing in this respect. Random mating of the population for one generation would have no effect on test cross variance so far as individual loci are concerned.

Experimental data for grain yield were in good agreement with the expected results based on genetic theory. In populations produced by intercrossing S₁ lines, a generation of sib-pollination within intercross progenies increased the esimate of test cross variance from 0.046 to 0.141 where an increase of 50% was expected. Where S₂ lines had been intercrossed, a generation of inbreeding increased test cross variance from zero to 0.172. It was concluded that a generation of inbreeding prior to initiation of a new cycle would be a worthwhile step in recurrent selection programs.

² Agronomist, Florida Agricultural Experiment Stations, University of Florida, Gainesville, Fla. 32601.

Received for publication March 5, 1967.