Accumulation of Dry Matter and Nitrogen in Durum Wheat During Grain Filling as Affected by Temperature and Nitrogen Rate

Durum wheat (Triticum durum Desf.) is commonly grown in mediterranean conditions, where temperature stress during grain filling can limit productivity. This study was conducted to assess the effect of optimal and too high temperature during grain filling on the patterns of accumulation of dry matter and N of durum wheat plants grown at different levels of N fertilization. Two durum wheat varieties, Appio and Creso, were grown in controlled environment conditions and in pots with three rates of nitrogen fertilizer (not applied, normal amount, and high amount) and two air temperature regimes during grain filling (20/15 °C and 28/23 °C day/night). Results showed that the duration of the intervals between the main maturity stages within grain filling were both genotype-specific and temperature- dependent, while N rate did not modify the timing of grain development. The two genotypes responded to temperature by increasing the rate of development, but the thermal timing of development was unchanged with the two temperature regimes. The higher temperature reduced grain growth and increased N accumulation in grain. However, these effects were recorded only in fertilized plants. Nitrogen availability modified the growth of the plant during the whole cycle, in that increased N fertilizer at seeding resulted in a greater plant size at anthesis and in a greater accumulation rate of dry matter and N in grain during grain filling. Grain yield and kernel weight were better expressed at 20/15 °C, while grain protein concentration was favoured under the 28/23 °C temperature regime. Nitrogen fertilization increased the sensitivity of plants to high temperature. Thus, the role of N fertilization under heat stress may be more important than under optimal temperatures.