Cultivar, Nitrogen, and Soil Water Effects on Apex Development in Spring Wheat1

Abstract

AbstractA better understanding of the growth and yield determining traits of spring wheat (Triticum aestivum L.) is important to development of improved cultivars, management practices, and growth simulation models. The objectives of this research were to evaluate cultivars, soil water content, and fertilizer N with respect to development of the main stem apex under field conditions. The experiment was conducted over 4 years on a Williams loam soil (fine‐loamy, mixed Typic Argiborolls). Cultivars of hard red spring wheat and durum wheat (T. turgidum L.) averaged 17.6 and 20.2 days, respectively, from emergence to apex double‐ridge formation. Cultivars of hard red spring wheat also differed significantly in accumulated growing degree days (GDD) to double‐ridge formation. Plant growth stage at apex double ridge as determined by the Haun scale, differed among hard red spring wheat cultivars. In general, cultivars that had a longer vegetative apex development stage had a higher Haun score at double‐ridge formation and also higher grain yields. Apex development of the hard red spring wheat cvs. Olaf, James, and Alex grown with two fertilizer N levels and three soil water levels was affected more by cultivar than by soil water content or fertilizer N level. The seven‐leaf cv., James, compared with eight‐leaf cvs., Olaf and Alex, generally had a shorter duration apex vegetative growth stage and spikelet development stage, required fewer GDD to reach double‐ridge and terminal spikelet stages, and developed double‐ridges and terminal spikelets at a lower Haun score. Stepwise regression analyses indicated that differences in grain yield and spikes/plant at harvest could be partly explained by duration of apex development to double ridges and the terminal spikelet expressed in days, accumulted GDD, and Haun score. Yield and spikes per plant were also associated with the number of spikelets/spike.