Dynamic Leaf Physiology and Architecture Shape Fusarium Head Blight Resistance in Wheat

Fusarium head blight (FHB) severely impacts wheat yield and grain quality, threatening global food security. In a field experiment, key photosynthetic, water relations, and leaf angular (morphological) traits were measured in the flag leaves of FHB-resistant and FHB-susceptible wheat genotypes under <i>Fusarium</i>-inoculated conditions. Measurements were conducted at 10 and 18 days post-inoculation (dpi) to evaluate the genotype- and time-dependent physiological and structural responses of resistant vs. susceptible genotypes to FHB infection over time. <i>Fusarium</i> infection induced distinct time- and genotype-specific changes across multiple physiological traits. At 10 dpi, when no visible symptoms were observed in either genotype, the resistant variety exhibited increased stomatal and total conductance, enhanced transpiration, earlier reductions in vapor pressure and H₂O mole fractions, improved photosynthetic efficiency, and dynamic leaf pitch adjustments, while the susceptible variety decreased them. By 18 dpi, the resistant genotype had recovered water vapor dynamics and reversed leaf pitch changes, whereas the susceptible variety continued to exhibit physiological disruption. These results are consistent with the possibility that the coordinated regulation of water vapor conductance, leaf water status, photosynthetic performance, and leaf orientation contributes to FHB resistance. Understanding the interplay between physiological and morphological traits at early infection could guide targeted breeding strategies and early phenotypic selection tools.