The role of pericarp cell wall components in maize weevil resistance

The maize weevil (MW), Sitophilus zeamais (Motsch.), is a storage pest that causes serious losses in maize (Zea mays L.) in developing countries. This study was conducted to investigate the role of pericarp cell wall components as factors that contribute to MW resistance in nine genotypes of tropical maize. Six susceptibility parameters to MW were measured and related to cell wall components such as simple phenolic acids, diferulic acids (DiFAs), hydroxyproline-rich glycoproteins (HRGPs), and nutritional and physical traits. Weevil susceptibility was negatively correlated (P < 0.001) with total DiFAs (r = -0.77), HRGPs (r = -0.82), grain hardness (r = -0.87), pericarp/whole kernel (P/K) ratio (r = -0.68), and pericarp thickness (r = -0.86). A detailed analysis of phenolics indicated the presence of trans-ferulic acid (FA),p-coumaric acid (CA), and four isomers of DiFA. The most prominent were 5,5'-DiFA, 8-O-4-DiFA, and 8,5'-DiFA benzofuran form (DiFAb). On the basis of regression models, 5,5'-DiFA, 8-O-4-DiFA, trans-FA, and p-CA were the most important phenolic components of resistance. Grain hardness was correlated (P < 0.001) with cell wall bound HRGPs (r = 0.61) and DiFAs (r = 0.75). Cell wall cross-linking components could contribute to MW resistance by fortification of the pericarp cell wall as well as increase grain hardness. This structurally based mechanism should be considered in the development of hybrids and varieties where storage pests are prevalent.