Contribution of the maize germ (Zea mays L.) to the resistance to the postharvest pests Sitophilus zeamais and Prostephanus truncatus.

Abstract

Maize (Zea Mays L.) is the most important cereal in terms of production. The maize weevil (Sitophilus zeamais) and the large grain borer (Prostephanus truncatus) are the two main postharvest insect pests that affect maize, causing losses as high as 80%. Factors attributed to resistance of maize kernels against insect pests have been widely studied in kernel structures such as pericarp, aleurone layer and endosperm. However, one structure that hasn’t been studied in this area is the germ. The aim of this study was to evaluate the contribution of the maize germ to the resistance to the attack of the postharvest insect pests S. zeamais and P. truncatus. For this purpose, we performed kernel-insect interaction assays with a duration of 60 days, testing both postharvest pests and 14 maize genotypes. For this work, we considered whole kernels and the hand-dissected germ. We recorded the main suceptibility parameters: grain weight loss, mortality rate, adult progeny and the mean development time of the pests. In order to define a group of possible metabolites which could be implicated in this resistance, we evaluated the chromatographic profiles (HPLC-DAD) of the 14 genotypes in term of phenolic compounds, in free and bound forms. We also evaluated the profile of tocopherols, phytosterols and fatty acids. Finally, we established the correlation between the susceptibility parameters determined in the insect bioassays and the evaluated compounds. Surprisingly, in the maize germ assays, although oviposition was observed after 60 days, there was no evidence of adult or larvae emergence of both pests. Furthermore, oleic acid showed a positive correlation with germ weight loss in both insect pests, while palmitic acid had a negative correlation of this parameter only in P. truncatus. Statistical differences in concentration of compounds from basal state and infested samples were detected in free and bound phenolics and liposoluble compounds. These findings provide strong evidence of an important contribution of the maize germ in the resistance against S. zeamais and P. truncatus by possible detrimental effects on early stages of development. This information could be helpful in the development of new strategies for the protection of maize kernels against S. zeamais and P. truncatus.