Divergent recurrent selection for vegetative phase change and effects on agronomic traits and corn borer resistance

Vegetative phase change, or the transition from juvenile vegetative to adult vegetative tissues, is essential to the lifecycle of higher plants. In maize (Zea mays L.), juvenile and adult vegetative tissues have distinctly different traits that may confer differing amounts of resistance to disease and insect infestations. Vegetative phase change has been linked to resistance to insects and common rust (Puccinia sorghi Schwein.). Seven cycles of divergent recurrent selection for early and late phase change were evaluated to determine effects of selection on phase change, insect resistance, and agronomic traits. Last leaf with juvenile wax, a trait indicative of the timing of phase change, was the selected trait. Divergent recurrent selection was effective in creating populations that underwent vegetative phase change at distinctly different developmental stages. Last leaf with juvenile wax moved from leaf 8.70 in the original population to leaf 14.48 in the late direction and 6.04 in the early direction. First leaf with adult wax moved from leaf 6.36 in the original population to leaf 8.15 in the late direction and 5.28 in the early direction. Several agronomic traits were also significantly altered by selection including plant and ear height, leaf number, kernel row count, and days to silking. C7Late plants averaged four more leaves and were taller and later flowering than C7Early plants. European corn borer (Ostrinia nubilalis Hubner) feeding damage on the second leaf above the ear was significantly greater in the late phase change direction, and significantly correlated with last leaf with juvenile wax. Most ear traits and European corn borer stalk damage resistance were not altered in a consistent way by selection.