Resistance of maize to the corn leaf aphid: A review

The corn leaf aphid [Rhopalosiphum maidis (Fitch)] is a worldwide pest of maize (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], barley (Hordeum vulgare L.), and wheat (Triticum aestivum L. em. Thell.). Breeding efforts toward resistance to the corn leaf aphid, however, have been limited. The aphid is present every year in the U.S. and significant insect populations are associated with grain yield loss and virus transmission. All parts of the maize plant are subject to injury, although aphid infestation produces the greatest damage in the tassel, causing varying degrees of barrenness. Phenotypic and genotypic responses of land races, pure-lines, and hybrids of maize indicate that resistance to the corn leaf aphid is inherited. Inheritance of resistance, however, has been reported to be simple as well as complex across different genetic backgrounds. Additive gene effects have been found to be the predominant type of gene action. Therefore, multiple genes with large environmental influence might be involved in resistance. Climatic conditions play an important role in determining the rate of colony development and grain yield reduction. Biochemical and physical barriers to the corn leaf aphid have been successful in some cases as well as biological control through numerous aphid predators. Cultural and chemical mechanisms of control are the most common method of limiting corn leaf aphid populations. Breeding for aphid resistance in maize continues to be a challenge due to the difficulty in obtaining reliable natural infestations and the presence of genotype by environment interactions.