Compensatory mechanisms associated with the effect of spring wheat seed size on wild oat competition
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Crop seed size affects the competitive relationship between spring wheat (Triticum aestivum L.) and wild oat (Avena fatua L.). However, the mechanisms associated with the process are not known. The effect of wheat seed size on wild oat competition was assessed by a mechanistic approach involving yield and its determinants in these species. Wheat plants established from large and small seed were evaluated under different seeding rates and wild oat densities during 19992001 near Kalispell, MT. Linear structural model systems based on ontogenic diagrams were constructed for each seed size class. Spikes m2 and panicles m2 had the greatest positive effect on yield within each species. For wheat, the impact of the two laterformed yield components on yield decreased in an ontogenic manner, whereas for wild oat, their relative contributions were similar in magnitude. Wheat plants derived from large seed had a noticeable negative effect on wild oat via a reduction in panicles m2 and seed weight, whereas wheat established from small seed mainly affected wild oat panicles m2 Wild oat competition reduced wheat spikes m2 and kernels spike1 in both seed size classes. However, these reductions were less for plants derived from large seed, which demonstrated enhanced compensatory ability. In summary, nongenetic variations in crop seed size affected the competitive dynamics between these species, where the major cropweed interference mechanism involved wild oat seed weight.
