Response to Fusarium graminearum infection in the rachis of a resistant and a susceptible wheat genotype

Fusarium head blight is a globally devastating disease of wheat, for which sources and mechanisms of resistance are urgently needed. The goal of this research was to elucidate the chemical nature of changes incurred in the rachis of a susceptible wheat (‘Chinese Spring’, CS), and a related addition line (CS-7EL) with resistance conferred by a fragment of the 7E chromosome from a wild wheat relative (Thinopyrum elongatum) in response to infection by Fusarium graminearum. Gravimetric analysis, followed by more targeted extractions and hydrolyses was used to study responses in the rachis of both genotypes at 7 days after fungal and mock inoculations. The most significant changes in the gravimetric analyses were an increase in the proportion of lignin in CS-7EL, and an increase in the proportion of hot water soluble compounds in CS. HPLC analysis of sugar profiles indicated higher degradation of arabinoxylan and cellulose in CS compared with CS-7EL. Differences were also observed in the profiles of the free, conjugated, and bound phenolic fractions for both varieties, with the conjugated fraction showing the greatest variation. The dominant phenolic acid in all samples was p-coumaric. A biplot analysis incorporating phenolic and sugar data was employed to provide an overview of responses to mock- and Fusarium-inoculation in CS and CS-7EL. Overall, our results suggest cell wall degradation in CS, and fortification in CS-7EL via increased lignification, in response to Fusarium infection.