How septoria leaf blotch affects nitrogen dynamics, grain yield and protein concentration in wheat

Septoria Leaf Blotch (Zymoseptoria tritici P. Crous) (SLB) is one of the most important biotic limitations of wheat (Triticum aestivum L.). This work analyzed the area under the disease progress curve, healthy area duration, crop growth rate, N dynamics, grain yield, grain protein concentration and grain protein content in wheat cultivars under three different inoculum concentrations of the pathogen. The highest area under disease progress curve values were found in the inoculated treatments. The increase in inoculum concentration reduced the healthy area duration and crop growth rate, affecting grain yield. The SLB declined N remobilization, whereas the N post-anthesis uptake was less affected, producing a lower N accumulation in the grain. In addition, a downward trend in the N harvest index was observed. Despite these reductions, the grain protein concentration and grain protein content increases were associated with a higher N concentration in the grain due to a decrease in the thousand kernel weight in the diseased treatments. The healthy area duration showed a significant and positive relationship with the crop growth rate, N remobilization, N post-anthesis uptake, and N accumulation in the grain in both years. The cultivars with the highest yield loss caused by the SLB had higher increases in grain protein concentration. The effects of this hemibiotrophic pathogen were not as consistent as those of pure biotrophic or necrotrophic pathogens. Although the biotrophic phase affected the dynamics of N, the grain protein concentration increased due to the effect of Z. tritici suggesting that the necrotrophic stage of this pathogen is the main contributor to these effects.