Fusarium verticillioides seed inoculation modifies maize cell wall responses to subsequent Sesamia nonagrioides infestation.

Abstract

Maize resistance to stem borers and fungal infection is strongly influenced by cell wall composition, but little is known about how prior fungal seed colonization affects subsequent insect-induced cell wall responses. Therefore, this study evaluated whether seed inoculation with Fusarium verticillioides modifies constitutive and induced cell wall defences against Sesamia nonagrioides infestation in maize. Seven maize inbred lines were grown under four treatments combining the presence or absence of F. verticillioides seed inoculation and S. nonagrioides infestation. Tunnel length, lignin content and composition, and cell wall-bound hydroxycinnamates were quantified in stem pith tissue. Treatment effects were mainly detected in lignin composition and hydroxycinnamate accumulation, whereas total Klason lignin and p-coumaric acid were not significantly altered. In non-inoculated plants, S. nonagrioides infestation reduced syringyl lignin subunits (S), ferulic acid and diferulate contents. In contrast, in plants derived from F. verticillioides-inoculated seeds, insect infestation increased ferulic acid and diferulates and shifted lignin composition, reducing S and the syringyl/guaiacyl ratio (S/G) while increasing guaiacyl lignin subunits (G). These responses were strongly genotype-dependent. A multiple regression model indicated that constitutive levels of S, ferulic acid, p-coumaric acid and diferulate 8-O-4, together with induced changes in G, explained most of the variation in relative tunnel length. Overall, these results show that maize resistance to S. nonagrioides involves both constitutive cell wall traits and inducible cell wall remodelling, and that prior seed colonization by F. verticillioides can modify the direction and magnitude of these responses, highlighting the importance of stress history and genotype in maize defence.