Effect of Temperature and Fertilizer N on Apex Development in Spring Wheat

Development of crop growth simulation models has indicated a lack of information on effects of specific environmental factors on growth and yield of hard red spring wheat, Triticum aestivum L. em Thell. One environmentally sensitive yield component is the number of kernels per ear. The objective of this research was to determine effects of temperature and fertilizer N on early plant growth, apex development, and number of spikelets and kernels per ear. ‘Sinton’ spring wheat was grown in a controlled environment chamber at 10, 18, and 26 C with 0, 78, and 224 kg Nha. Irradiance was 1,000 µEm⁻ ˢᵉᶜ⁻¹ and 16-hour photoperiod. Duration of the vegetative phase of the apexes was determined for the main stem (M) and the first (Tl), second (T2), and third (T3) tillers and duration of the spikelet development phase was measured for M. Tillers and leaves were tagged as they appeared and their development related to apex development. Spikelets and kernels per ear were determined for each stem at maturity. Duration of M apex vegetative phase was influenced by temperature but not by N level; the spikelet development phase was influenced by both temperature and N level. Duration of the vegetative phase was 24, 22, and 17 days at 10, 18, and 26 C, respectively. Duration of the spikelet development phase was significantly shorter at 26 C (4.8 days) than at 10 C (6.5 days) and 18 C (7.4 days). Development of tiller apexes appeared to be strongly synchronized to development of the M apex. Inflorescence initiation on M occurred at the 5.1 leaf stage at 18 C and at 4.4 leaf stage for both the 10 and 26 C treatment. Kernels per ear for the main stem and tillers decreased significantly from 27.2 and 24.8, to 18.5 as temperature increased from 10 to 18 to 26 C, respectively. Fertilizer N levels of 0, 78, and 224 kg Nha produced kernel numbers of 20.8, 23.5, and 26.2, respectively. Tillers originating at the coleoptile node produced fewer kernels per ear at 10 C than leaf tillers, but not at 18 or 26 C. The percentage of first tillers elongating from the coleoptile node was 62, 47, and 30 at 10, 18, and 26 C, respectively Results show that early vegetative growth and apex development is more sensitive to temperature than to N fertilization. Kernels per ear for tillers is controlled in part by their synchronization to the development of the M apex.