Studies of corn root morphology, canopy description, light and nutrient relationships, have focused on conventional corn hybrids. We are now extending these studies to other corn types with contrasting canopy and root architectures. Field and greenhouse experiments were carried out in order to characterize root morphology, N status in the plant and its relationship with yield and yield components, canopy architecture and light interception of these genotypes. The indoor experiments investigated root morphology and how N affects it. Root fractal geometry and its relationship with standard measured root variables were investigated. The field research, at two sites and over two growing seasons, examined (i) maize canopy architecture with regard to light interception and (ii) nitrogen effects on grain yield of different maize genotypes. Four genotypic types were included: (i) Leafy reduced-stature, Lfy1rd1 (LRS), (ii) non Leafy-reduced stature, lfyrd1 (NLRS), (iii) Leafy normal stature, Lfy1Rd1 (LNS), and (iv) conventional commercial hybrids, lfy1Rd1. Pioneer 3905 served as the check hybrid for late maturity, and Pioneer 3979, the check for early maturity. The work allowed development of following methods: (i) root sampling for measurement of large root systems, (ii) staining to enhance root contrast for measurement with a scanner-based software system, (iii) sample size determination for SPAD meter readings, and (iv) the design and construction of a mobile and multi-strata device for measurement of light interception. Data were collected for mathematical characterization of canopies (i.e. leaf angle, co-ordinates of the maximum height of the leaf, co-ordinates of the leaf tip), plant N status (SPAD meter readings), light interception, yield and grain yield components. Conventional hybrids generally showed greater root length and surface area than their leafy genotypic counterparts at early developmental stages (i.e. up to 15 days from emergence). However, Leafy geno

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Previous studies on Leafy reduced-stature (LRS) maize found that it had extremely early maturity and a higher harvest index (HI), leading to high yields for its maturity rating. Whether this apparent high HI is relaxed to its earliness, or can also exist among the medium or late maturity LRS maize has not been previously investigated. It was also of interest to know if the traits that produced the LRS canopy structure have pleiotropic effects on root architecture. Finally, field observations indicated that LRS maize had a lower incidence of common smut. It is not known whether this apparent resistance is specific to smut or includes other diseases. / Using a wide range of the most recently developed LRS hybrids and some conventional hybrids, a two-year field experiment was conducted to examine the HI and disease resistance of LRS maize. HI, yield, and yield components were compared between the two genotype groups (LRS and conventional) under different population densities. The resistance to the natural incidence of common smut and artificially inoculated Gibberella ear rot was also tested. Morphology and fractal dimension analyses of roots at an early development stage were conducted in indoor experiments. These analyses were performed with WinRHIZO (version 3.9), an interactive scanner-based image analysis system. / This work showed that: (1) There was no relationship between the HI and maturity; higher HIs can also exist among the medium and late maturity LRS hybrids. (2) While LRS maize hybrids have the potential for high yield this was not realized in the LRS hybrids used in this work. Further breeding and development of optimum management practices are needed to fully exploit this potential. (3) During early development LRS hybrids generally had more branching and more complex root systems than conventional hybrids. (4) Fractal dimension, as a comprehensive estimation of root complexity, was highly related to major root morphological variables, such as root total length, surface area, branching frequency and dry mass. (5) Of the hybrids tested the greatest resistance to both common smut and Gibberella ear rot, two major ear diseases, occurred in some of the LRS types.

The importance of root systems for soil-based resource acquisition by plants has long motivated researchers to quantify the complexity of root system structures. However, most of those studies proceeded from 2-D spatial data, and thus lacked the relevance of a 3-D analysis. In this project, helical CT scanning was applied to study root systems with an unprecedented level of accuracy, using non-destructive and non-invasive 3-D imaging that allowed for a spatio-temporal analysis. The appropriate CT scan parameters and configuration were determined for root systems of maize seedlings grown in sand and loamy sand. It was found that the soil conditions allowing for better visualization were sand before watering and loamy sand after watering. Root systems were CT scanned and visualized either at a single moment in time or repeatedly on successive days. Complexity analysis was performed by estimating the fractal dimension on skeletonized 3-D images of root systems.

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