High nitrogen levels reduce the damage caused by Pyrenophora tritici-repentis by maintaining the photosynthetic performance of wheat cultivars with contrasting resistance

Abstract

Pyrenophora tritici-repentis (Ptr) (Died.) Drechs, the causal agent of tan spot in wheat, is a disease of significant economic impact in Brazil and worldwide. In this study, we examined the effect of different nitrogen (N) levels (70, 130, and 200 kg ha⁻¹) on two wheat cultivars (TBIO Audaz and TBIO Tibagi), which exhibit different degrees of basal resistance to tan spot. We focused on their pathometric and physiological responses under controlled conditions. For both wheat cultivars, applying 200 kg N ha⁻¹ extended the incubation period (IP) by 19 %, along with reduction of final lesion size (LS), disease severity, and the area under the disease progress curve (AUDPC) up to 29, 18, and 26 %, respectively, compared to plants fertilized with 70 kg N ha⁻¹. The fast chlorophyll a fluorescence (OJIP-test), conducted at 7 and 14 days after inoculation (dai), showed changes in the fluorescence dissipation pattern compared to 0 dai, regardless of N level. However, wheat cultivars fertilized with 70 kg ha⁻¹ of nitrogen and Ptr infected demonstrated significant alterations in parameters related to the functional stability of the photosynthetic machinery, with changes of 50 % in F_v/F_m, V_j, ψE₀, φD₀, and M₀. Additionally, photosynthetic pigment pools were reduced by 47 % by Ptr infection. However, these negative effects can be mitigated using adequate N levels and using moderately resistant cultivars, which contribute to reduced tan spot severity and improved physiological response in wheat. These results highlight the needs of attention to provide adequate levels of nitrogen to improve tan spot control.