Comparative Enzymatic and Gene Expression Responses in Wheat to DON- and NIV-Producing Fusarium Species

<i>Fusarium</i> head blight (FHB) is a major threat to wheat production that is caused by toxigenic species of the <i>Fusarium graminearum</i> complex. This study aimed to investigate the biochemical and molecular defense responses of Brazilian wheat genotypes (BRS 194, BRS Parrudo, and Frontana) with contrasting FHB susceptibilities following inoculation with <i>F. graminearum</i> (deoxynivalenol producer) and <i>F. meridionale</i> (nivalenol producer). Temporal patterns of antioxidant enzymes, defense-related enzymes, and gene expression (<i>ABC-Transporter</i> and <i>Ca²⁺-ATPase</i>) were analyzed from 12 to 96 h after inoculation. The ANOVA results revealed significant effects of genotypes, inoculation, and time after inoculation on most of the evaluated enzymatic activities. Frontana exhibited high basal activity for most enzymes, and after inoculation, the enzyme activity was higher than in other genotypes. BRS 194 presented delayed and fragmented activation patterns, particularly under DON-producing pathogen infection. According to the transcriptome results, inoculation with the NIV-producing pathogen upregulated both genes, reaching up to an 18-fold increase. BRS 194 showed an upregulated transcript pattern from the early hours after inoculation. Frontana showed increased transcript levels, reaching 12-fold, under DON-producing pathogen infection. These findings show that biochemical and molecular responses varied depending on genotype and the chemotype of the <i>Fusarium</i> isolate, highlighting the importance of early, coordinated defense activation in FHB resistance.