Natural Selection in a Doubled‐Haploid Mixture and a Composite Cross of Barley1

Abstract

Natural selection can modify cereal breeding populations that are advanced in bulk. Its effects may vary among populations and environments. We examined changes in two barley (Hordeum vulgare L.) populations of similar ancestry: an F₃ composite cross and a mixture of doubled‐haploid (DH) lines. Bulk plots of these populations were grown in Ontario, in Prince Edward Island, and with alternation between Ontario and Prince Edward Island. After 5 yr, the grain yields, heading dates, and plant heights of 50 random lines from each of eight resulting populations were evaluated at two locations in Ontario. On the average, these lines were higher yielding, later heading, and taller than the original DH lines. Composite‐cross populations, which would have had potential for segregation, recombination, and heterosis during the natural selection period, had higher mean yields and later mean heading dates than did DH mixtures. Alternated populations were lower yielding and taller, and retained greater variability for plant height, than nonalternated populations. Populations grown or initiated in Ontario were higher yielding than those grown or initiated in Prince Edward Island. Genotype by testing location interactions were not important. Correlations among traits were affected by natural selection, but not in any consistent direction. It was concluded that natural selection can favorably affect grain yield, but may unfavorably affect maturity, plant height, and relationships among traits. Natural selection was less effective when material was advanced outside its intended region of adaptation, or was alternated between locations.