INBREEDING AND THE TIMING OF VEGETATIVE PHASE-CHANGE IN MAIZE (ZEA-MAYS L.)

Vegetative development in maize (Zen mays L.) can be divided into juve nile and adult phases, each with distinct anatomy and physiology. Vege tative phase change occurs at the node(s) at which juvenile-vegetative traits are replaced by adult-vegetative traits. The objective of this study was to determine the effects of inbreeding in a sugary1 populat ion of 'Minn11' C3 (pseudostarchy) on several phase-specific, developm ental traits that are used as markers of the timing of vegetative phas e change. All agronomic traits had significant, linear changes between the S-0 and S-5 generations, including decreased leaf length, leaf wi dth? ear height, and plant height, and later flowering time. Changes o f this type are normally associated with inbreeding depression. In con trast, phase-specific, developmental traits generally did not exhibit inbreeding depression. Tiller number was the only phase-specific, deve lopmental trail: thar showed a significant, linear response over gener ations. Our results suggest that most phase-specific, developmental tr aits are governed primarily by additive effects with dominance effects occurring only for tiller number. Breeders should be able to successf ully include most phase-specific, developmental traits in selection in dices. In addition, studies assessing the timing of vegetative phase c hange based on phase-specific, developmental traits should have only t iller number confounded by different levels of inbreeding among entrie s.