Spikelet initiation of winter triticale and winter wheat in response to nitrogen fertilization

Spikelet initiation in response to two levels of nitrogen fertilization (0 and 200 kg N ha(-1) split into 5 x 40 kg N ha(-1)) was investigated on the main stem and the first initiated tiller of winter triticale (Triticosecale WITTM., cv. Grado) and winter wheat (Triticum aestivum L., cv. Taras) grown at Rostock, Germany (54.2 degrees N) in four seasons (1987-1991). Plants were sampled every 3-10 days between plant emergence and anthesis, and the number of spikelet primordia, the lengths of the shoot apex and shoot were recorded. Nitrogen effects on spikelet number per ear were analyzed at the end of the rapid rate of spikelet initiation (EorSI) and at anthesis. The duration of spikelet initiation was not affected by nitrogen application in both cereals. The numbers of spikelets of both main stems and tillers were significantly increased due to nitrogen fertilization at EorSI and anthesis (2.3 and 2.6 spikelets per ear, respectively) in wheat. Nitrogen fertilization did not affect spikelet number per ear at EorSI in triticale but significantly increased spikelet number on main stems and tillers at anthesis (2.4 spikelets per ear), which was explained by the continuation of spikelet initiation after EorSI in the high-nitrogen treatment and spikelet abortion in the treatment without nitrogen application. Spikelet abortion was observed in both nitrogen treatments in wheat. Main stems initiated more spikelets per ear than tillers. However, spikelet initiation on main stems and tillers did not respond differently to nitrogen application for triticale or wheat. Variation of spikelet initiation among years was affected by nitrogen application. In wheat, spikelet number per ear varied less among years when nitrogen was applied. In triticale, the variation in spikelet number increased with nitrogen application. There was a positive relationship between the duration of spikelet initiation and the nitrogen effect on spikelet number per ear at EorSI for triticale. In both cereals, nitrogen application increased both the length of the shoot and the length of the shoot apex, which, however, did not result in a relationship between the effects of nitrogen application on spikelet number and either shoot length or apex length. Spikelet initiation in response to nitrogen fertilization of triticale and wheat is discussed with respect to differences in the developmental performance and the morphological characteristics of the apical differentiation between the two cereals. It is concluded that spikelet initiation in triticale was better adapted to low nitrogen conditions than wheat. Our results suggest that consideration of nitrogen supply is important when analysing the variation in spikelet initiation and relationships between growth and differentiation processes.