Inbreeding and the timing of vegetative phase change in maize (Zea mays L.)

Vegetative development in maize (Zen mays L.) can be divided into juvenile and adult phases, each with distinct anatomy and physiology. Vegetative 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 population of 'Minn11' C3 (pseudostarchy) on several phase-specific, developmental traits that are used as markers of the timing of vegetative phase change. All agronomic traits had significant, linear changes between the S-0 and S-5 generations, including decreased leaf length, leaf width? ear height, and plant height, and later flowering time. Changes of this type are normally associated with inbreeding depression. In contrast, phase-specific, developmental traits generally did not exhibit inbreeding depression. Tiller number was the only phase-specific, developmental trail: thar showed a significant, linear response over generations. Our results suggest that most phase-specific, developmental traits are governed primarily by additive effects with dominance effects occurring only for tiller number. Breeders should be able to successfully include most phase-specific, developmental traits in selection indices. In addition, studies assessing the timing of vegetative phase change based on phase-specific, developmental traits should have only tiller number confounded by different levels of inbreeding among entries.