VARIATION FOR STEM SOLIDNESS AND ITS ASSOCIATION WITH AGRONOMIC TRAITS IN SPRING WHEAT

The wheat stem sawfly (Cephus cinctus Norton) is a major insect pest o f spring wheat (Triticum aestivum L.) in the Northern Great Plains of the US and Canadian Prairie provinces. The development of solid-stemme d wheat cultivars has been the main strategy to minimize losses from t his insect. Solid-stemmed cultivars generally yield less than hollow-s temmed cultivars of the same era, and there are reports that degree of stem solidness is inversely related to grain yield. Our purpose was t o examine the association between stem solidness and other agronomic t raits and measure changes in progeny performance from three solid-stem med parents representing different eras of cultivar development. Rando m, F-4-derived F-6 lines were obtained from crosses between solid-stem med Rescue, Fortuna, and Lew and hollow-stemmed Newana and Thatcher. T he random lines plus parents were evaluated in three environments. Cha nges during time from Rescue to Lew were in the desired direction for days to heading, plant height, and test weight, while stem-solidness s core decreased for the parents themselves and in cross combination. Gr ain yield showed significant gains in two of three environments. A sig nificant solid-stemmed x hollow-stemmed parent interaction was observe d for stem solidness score suggesting epistatic gene action in the inh eritance of this trait. The only significant associations of stem soli dness score with agronomic traits were with plant height in one cross and grain protein concentration in two crosses. Results show the devel opment of high yielding, solid-stemmed cultivars is not limited by und esirable associations between degree of stem solidness and other agron omic traits.