Tocopherol contribution to the resistance against storage pest Prostephanus truncatus in maize

Abstract

Prostephanus truncatus infestation can cause losses as high as 80% on stored maize. Sources of resistance against this pest are related to the antioxidant capacity of the pericarp and aleurone layer structures, mainly due to phenolic acids content and their derivatives. Nonetheless, there is not enough information about the germ structure or the liposoluble antioxidants, such as tocopherols. To determine the contribution of tocopherols and liposoluble antioxidant capacity to the resistance against P. truncatus, thirteen genotypes of maize were tested in two confined bioassays (n=3). The first was to assess the susceptibility of each genotype. The second was with the enriched structure of the germ to gather information on damage and development of P. truncatus on this structure. Seven susceptibility parameters were recorded 7 and 60 days after infestation, and ten genotypes were selected based on a Susceptibility Selection Index, with five recognized as resistant and five as susceptible. HPLC-FLD was used to determine the content of tocopherols (δT, γT, and αT), and an ORAC assay was performed to measure the lipophilic antioxidant capacity among the ten genotypes selected. All Population 84 genotypes exhibited less damage by P. truncatus and were categorized as resistant. Three Population 84 genotypes were selected: P84C0Y (SI = 0.17), P84C4W (SI = 0.27; highest tocopherol content, 39.58 mg/kg; high L-AC, 429.04 μmol TE/g), and P84C4Y (SI = 0.51). Two selected genotypes previously recognized as susceptible were classified as resistant: Pink Creole (SI = 0.39; high tocopherol content 39.40 mg/kg; highest L-AC, 488.30 μmol TE/g) and Don Goyo (SI = 0.55). The most susceptible genotype was Red Creole (SI = 3.56; lowest L-AC, 205.48 μmol TE/g), the remaining 4 susceptible varieties selected were Peru2 (SI = 1.23), NAYA29B (SI = 1.07), Panchito (SI = 1.00; lowest tocopherol content, 11.21 mg/kg; low L-AC, 250.4 μmol TE/g), and Pozolero (SI = 0.97). Additionally, a strong correlation (p > 0.01) demonstrated that a short-length bioassay (7 days) can be comparable to a full-length bioassay (60 days). Both can measure a genotype susceptibility to P. truncatus based on weight loss, but only a full-length bioassay can provide information on adult emergence.