Varietal susceptibility of maize to larger grain borer, Prostephanus truncatus (Horn) (Coleoptera; Bostrichidae), based on grain physicochemical parameters.

Déthié Ngom,Cheikh Abdou Khadre Mbacké Dia,Paul Malumba,Marie-Laure Fauconnier,Mbacké Sembène,Cheikh Thiaw,Craig Eliot Coleman

doi:10.1371/journal.pone.0232164

Abstract

Maize (Zea mays L) is one of main nutrients sources for humans and animals worldwide. In Africa, storage of maize ensures food resources availability throughout the year. However, it often suffers losses exceeding 20% due to insects such as the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera; Bostrichidae), major pest of stored maize in the tropical countries. This study aims to select resistant varieties to reduce maize storage losses and explain the physicochemical parameters role in grains susceptibility. In the first study, maize grains were artificially infested under no-choice method with insects. Susceptibility parameters such as weight loss, grain damage, number of emerged insects, median development time and susceptibility index varied significantly through maize varieties. Dobie susceptibility index (SI) was assessed as a major indicator of resistance. The most resistant varieties were Early-Thaï, DMR-ES and Tzee-Yellow. Conversely, Synth-9243, Obatampa and Synth-C varieties were susceptible. SWAN, Across-Pool and Tzee-White were classified as moderately resistant varieties. The insect reproductive potential was significantly different in the nine maize varieties and Early-Thaï, DMR-ES and Tzee-Yellow varieties were the least favourable host. To assess the relationship between grains physicochemical characteristics and varietal susceptibility, moisture, total phenolics, palmitic acid, proteins, amylose, density and grain hardness were evaluated according to standardized methods. Palmitic acid, SI, insects emerged and grain damage were significantly and positively correlated with each other, and negatively correlated with grains hardness, phenolics and amylose contents. Maize susceptibility index was significantly and negatively correlated to amylose, and phenolics contents and positively correlated to palmitic acid content. This study identified three resistant maize varieties to P. tuncatus and revealed that the major factors involved in this resistance were hardness, phenolic and amylose contents of grains.

Highlights

Ensuring global food security, nutrition and livelihood is one of the main challenges for the 21st century
Number of insects emerged from Synth-9243 variety was 9 times higher than that emerging from DMR-ES and Early-Thaï varieties, and 7 times more than that Tzee-Yellow variety
Our study showed the maize susceptibility to the larger grain borer could be explained by physical mechanisms and/or biochemical mechanisms such amylose, moisture, total phenolics, palmitic acid and crude protein contents, which have proved very different in our varieties

Summary

Introduction

Nutrition and livelihood is one of the main challenges for the 21st century. The infestation starts in the field and adults attack mainly whole or broken grains and flour during storage [10,11] In developing countries, this insect is a serious pest of economic importance, causing maize-grain losses during storage ranging from 30% [12] to greater 40% of total production in 6 months [13]. This insect is a serious pest of economic importance, causing maize-grain losses during storage ranging from 30% [12] to greater 40% of total production in 6 months [13] This beetle reduces maize germination, increases the grain’s moisture content [14,15] and facilitates the storage contamination by fungi and bacteria [16]. Most of farmers have not access to hermetic storage structures and fumigants due to availability and cost reasons

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