Genetic differentiation of winter wheat populations following exposure to two management systems in early inbreeding generations

Producers in the southern Great Plains usually dedicate fields of winter wheat (Triticum aestivum L.) to a grain-only (GO) management system or one that incorporates grazing preceding grain harvest (dual-purpose or DP system). We hypothesized that a grazing system may be applied as a selection tool during the early inbreeding generations to shift gene frequencies in favor of improved grazing tolerance and grain yielding ability. Grain yield and other key traits were compared among F5 bulk progenies of 24 populations exposed in the [F.sub.2] to [F.sub.4 ]generations to either system, including a Base set of [F.sub.3] progenies and three cultivars. From GO and DP experiments conducted for 3 yr near Marshall, OK, the grain yield loss from GO to DP systems was 11% for '2174' and 'Custer' and 24% for 'Jagger'. Yields of DP selections exceeded the GO selections when tested in the DP system (220 kg [ha.sup.-1] differential, P < 0.01) and in the GO system (80 kg [ha.sup.-1], P = 0.01), with neutral effects on grain volume weight and protein concentration. Vegetative growth habit of DP and GO selections were visibly differentiated. When targeting a DP management system, derivation of bulk populations for line selection should utilize the DP system as a selection environment during the early inbreeding generations. This approach should not carry a universal yield penalty for GO environments when the breeding target includes both DP and GO systems. doi: 10.2135/cropsci2009.05.0234