Mechanisms and Sources of Resistance in Tropical Maize Inbred Lines to Chilo partellus Stem Borers

Abstract

Developing maize with durable resistance to maize stem borers could be enhanced by identifying genotypes with different mechanisms of resistance and pyramiding the resistances into high yielding genotypes. This study was carried out on 120 CIMMYT tropical maize inbred lines to identify the most important mechanisms of resistance that could be used to discriminate the germplasm into resistant or susceptible categories. The experiment was laid in an α-lattice design, and replicated three times during the 2011/12 seasons. Traits measured were leaf toughness, stem penetrometer resistance, trichome density, stem sugar content, leaf damage, number of stem exit holes and stem cumulative tunnel length. A selection index was computed and categorized the 120 inbred lines into 33 resistant, 29 moderately resistant, 31 moderately susceptible and 27 susceptible. The most resistant lines were those derived from the CIMMYT multiple borer-resistant populations with CKSBL10039 being most resistant and CML395 most susceptible with indices of 0.49 and 1.84, respectively. Trichome density, leaf toughness and stem sugar content in that order were the most important traits in discriminating the lines into resistance and susceptible categories. More research is needed to classify the specific types of trichomes and sugars present in both resistant and susceptible inbred lines.

<strong>Factors Influencing Genomic Prediction Accuracies of Tropical Maize Resistance to Fall Armyworm and Weevils</strong>

“…The panel used in this study consisted of 358 maize lines with a diverse genetic and geographic background and were sourced from the National Crop Resources Research Institute (NaCRRI/Namulonge, Uganda), the International Institute for Tropical Agriculture (IITA/Ibadan, Nigeria), and The International Maize and Wheat Improvement Center (CIMMYT/Nairobi, Kenya). The panel consisted of 71 inbred lines developed for various purposes at NaCRRI, 28 and five stem borer (SB)-resistant inbred lines from CIMMYT (6,13,14) and IITA, respectively, 19 storage pest (SP)-resistant inbred lines (7,8) and a doubled haploid (DH) panel of 235 lines developed at CIMMYT using six parents of which three were stem borer-resistant and one was a storage pest-resistant inbred line (these were also included in the population) and two were CML elite lines (one, CML132 was included in the panel) ( Table S1).…”

“…The fall armyworm (FAW) and stem borers in the field, and the maize weevil (MW) in storage facilities are some of the most devastating insect pests on the continent. These insect pests cause yield losses ranging from 10 to 90% leading to loss of grain marketability, and consumer health concerns due to the possible contamination of the grain with mycotoxin such as aflatoxins (3)(4)(5)(6). In Africa, tremendous efforts were made during the last two decades to build host plant resistance to insect pests in maize through traditional pedigree (phenotypic)-based selection (PS) with substantial desirable results.…”

Chemical bases for maize grain resistance to infestation and damage by the maize weevil, Sitophilus zeamais Motschulsky

“…Debate on the bases for maize grain resistance to S. zeamais infestation and damage is still on (Dobie, 1974;Shafique and Chaudry, 2007;Munyiri et al, 2013;Nwosu et al, 2015a). Grain hardness among other grain physical properties such as length, width, thickness and weight has been shown to be a basis for resistance to the attack of S. zeamais and some other insect pests of stored maize (Dobie, 1974;Osipitan and Odebiyi, 2007).…”

“…The use of conventional synthetic insecticide is effective, but its environmental implication and other demerits such as health hazards and high market price have discouraged its application (Munyiri et al, 2013). Host plant resistance is particularly important and can be a very useful technique in grain protection against stored product insects, because it is packaged in the grain, causes no hazard to the environment and is compatible with other control methods (Gemechu et al, 2011;Munyiri et al, 2013). In developing nations, maize weevil management options must necessarily include use of resistant variety as it is sustainable on account of entailing low cost and requiring little or no skill.…”

Genomic Prediction of Tropical Maize Resistance to Fall Armyworm and Weevils: Genomic Selection Should Focus on Effective Training Set Determination

“…Insect damage on maize plants and stored grains potentially impede food security in Africa (1)(2)(3). The fall armyworm (FAW) and stem borers in the field, and the maize weevil (MW) in storage facilities are some of the most devastating insect pests on the continent causing yield losses ranging from 10 to 90% leading to loss of grain marketability, and consumer health concerns due to the possible contamination of the grain with mycotoxin such as aflatoxins (3)(4)(5)(6). In Africa, tremendous efforts were made during the last two decades to build host plant resistance to insect pests in maize through traditional pedigree (phenotypic)-based selection (PS) with substantial results.…”