Inheritance of resistance in maize silks to the corn earworm

The corn earworm, Helicoverpa zea (Boddie), is a perennial economic pest of field crops in the United States. Maize, Zea mays L., is the major host crop promoting the build-up of devastating corn earworm populations that limit full production of cotton, soybean, peanut, and grain sorghum. Resistance to the corn earworm in maize and in particular sweet maize, would provide an environmentally safe, economical method of control for this pest insect. Antibiotic effects of corn silks on this insect are: small larvae, extended developmental period, and reduced fecundity. Silks from individual maize plants of resistant and susceptible lines and progeny in six generations consisting of parents (P₁, P₂), F₁, F₂, and backcrosses BC₁.₁ (F₁ × P₁) and BC₁.₂ (F₁ × P₂) from each of four crosses were used to determine the genetic basis of the antibiotic resistance of silks to the corn earworm. In the cross of Zapalote Chico × PI340856, genes controlling resistance in the silks to the corn earworm larvae are dominant in PI340856 to those in Zapalote Chico. The cross of Zapalote Chico × GT114 involves parents differing in degree of resistance, and possibly differing for the genetic mechanism by which the resistance is inherited. The inheritance of resistance may involve non-additive (dominance and epistasis) genetic variance. A digenic 6-parameter model indicated (1) the resistance in this cross is controlled by more than one pair of genes and (2) some or all of the genes interact to cause non-allelic interaction. Thus, the resistance in this cross may be controlled by both dominant and recessive genes. The resistance of Zapalote Chico × CI64, an intermediate inbred, is influenced by additive gene effects. The digenic model adequately predicts all generation means of the cross of GT3 × PI340856 except for the F1. Thus, it appears that the additive-dominance model is not satisfactory for this cross involving susceptible and resistant parents. Generation mean analysis indicates that resistance to silk-feeding by corn earworm larvae is under genetic control, but gene action differs from one type of cross to another.