Heterosis in Full‐sibs Within and Between Half‐sib Families in Open‐Pollinated Varieties of Maize1

Abstract

When the full‐sib reciprocal recurrent selection RRS(F) scheme is applied in a single open‐poliinated maize (Zea mays L.) population each random fuli‐sib (FS) family the result of a cross of plants from (a) within previous half‐sib (HS) family or (b) plants from different previous HS families. The effects of resulting differences in inbreeding on the heterosis in the two kinds of families were studied. Samples of each type were developed and evaluated in each of two maize populations. Grain yield, ear height, and moisture at harvest were considered. Results showed that FS between HS outyielded FS within HS families by 8.5 and 11.7% in the ‘Northwestern Dent’ variety and in ‘Early Flint’ composite, respectively. Assuming a 1% loss in yield for each 1% increase in inbreeding, both figures approach the 12.5% inbreeding coefficient calculated for FS within HS families.Full‐sibs made at random in a maize population are most likely to be FS between plants from different HS families. Some will not be. In the initiation of RRS(F) within a population, advantages exist where HS families are identified so as to assure that all FS arise from parents of different HS. Lower yielding FS formed from within HS family crosses will be avoided and not included in performance trials. This would enhance selection of superior FS crosses and increase genetic progress when a RRS(F) program is applied in maize breeding.