Influence of Winter Wheat Height on Competitiveness with Jointed Goatgrass

S.S. Seefeldt, A.G. Ogg, and R.E. Allen
1996 Proc. West Soc. Weed Sci. 49: 37Abstract. Jointed goatgrass is a troublesome weed in winter wheat in the Pacific Northwest as there are no selective herbicides for its control. Jointed goatgrass is highly competitive in a wheat crop, reducing yields in the field, and jointed goatgrass spikelets are difficult to serparate from wheat seed, increasing dockage at the market. Experiments are underway to identify plant characterisitics that make winter wheat more competitive against jointed goatgrass. One characterisitc that may be important in the competition equation is winter wheat height.

A field experiment was conducted at the Palouse Conservation Farm using near-isolines of ‘Nugaines’ winter wheat. These near-isolines, which had either Rht1 (reduced height gene 1), Rht2, Rht1+Rht2, or no Rht genes, were grown with and without jointed goatgrass. The experimental design was a randomized strip plot with 4 replications. Main blocks were jointed goatgrass treatments subplots were isolines and were 2.4 m by 15 m with 18 cm row spacing. Heights of the wheat isolines at physiological maturity were 51, 79, 77, and 101 cm for Rht1+2, Rht1, Rht2, and no Rht, respectively. When growing with the Rht1, Rht2, or no Rht lines, jointed goatgrass grew 80 cm tall. When growing with the short Rht1+2 line, jointed goatgrass height grew 69 cm tall. Under weed free conditions, the Rht1 and Rht1+2 lines yielded significantly more grain than the no Rht line. Grain yield form the Rht2 line was intermediate and not statistically different from the other three lines. When the wheat lines were grown with jointed goatgrass, wheat yields were reduced 39% in the Rht1+2 line, 37% in the Rht1 line, 30% in the Rht2 line, and 20% in the no Rht. There were significant differences in jointed goatgrass spikelet yields in the different isoline plots. Jointed goatgrass yielded the most spikelets when growing in competition with the Rht1+2 line and least with the no Rht line. Jointed goatgrass spikelet weights were the same in the Rht2 and Rht1 plots.

Increasing wheat height was an important factor in increasing competition against jointed goatgrass. However, there were some small differences in competitiveness between the Rht1 and Rht2 lines, which have equivalent heights. The Rht1 line yielded slightly higher in the weed free plots and reduced jointed goatgrass yields slightly more than the Rht2 line. In these near-isolines, there may be another characteristic in the Rht1 line that is enhancing its yield potential and its competitiveness against jointed goatgrass compared to the Rht2 line.