The lodging resistance of durum wheat is strongly affected by competition for light from the initiation of internode elongation to the end of the second internode elongation stage

Plant lodging prevents the achievement of high durum wheat yields. Although nitrogen is commonly applied to increase crop yields, it has been shown to induce lodging. Competition for light during the stem elongation stage is the main cause of this phenomenon. In this study, we investigated the relationships among lodging resistance, light competition, and nitrogen application in durum wheat by treating plants with different nitrogen application timings and shading. The length of the second internode (the most important position for evaluating lodging resistance) of both main stems and tillers was longer in plants treated with conventional high nitrogen application before the initiation of the stem elongation stage (GS30) and in those for which 75% of photosynthetically active radiation was obstructed using a shading net from GS30 to the end of the second internode elongation stage (GS32). The outer diameter and culm wall thickness were smaller in the conventional and shaded plots. The internode length, outer diameter, and culm wall thickness in the second internode reached 70–80% of their maximum values at the third internode elongation stage. The internode dry weight per unit length remained lower in the shaded plants than in their unshaded counterparts, even after shading removal. Light reception from GS30 to the end of GS32 affected lodging resistance but not the yield or nitrogen uptake. In conclusion, applying nitrogen after GS30 to reduce light competition from GS30 to the end of GS32 is important for enhancing lodging resistance in durum wheat.