Abstract
The mature root system is a vital plant organ, which is critical to plant performance. Commercial maize (Zea mays L.) breeding has resulted in a steady increase in plant performance over time, along with noticeable changes in above ground vegetative traits, but the corresponding changes in the root system are not presently known. In this study, roughly 2500 core root systems from field trials of a set of 10 diverse elite inbreds formerly protected by Plant Variety Protection plus B73 and Mo17 and the 66 diallel intercrosses among them were evaluated for root traits using high throughput image-based phenotyping. Overall root architecture was modeled by root angle (RA) and stem diameter (SD), while root complexity, the amount of root branching, was quantified using fractal analysis to obtain values for fractal dimension (FD) and fractal abundance (FA). For each trait, per se line effects were highly significant and the most important contributor to trait performance. Mid-parent heterosis and specific combining ability was also highly significant for FD, FA, and RA, while none of the traits showed significant general combining ability. The interaction between the environment and the additive line effect was also significant for all traits. Within the inbred and hybrid generations, FD and FA were highly correlated (rp ≥ 0.74), SD was moderately correlated to FD and FA (0.69 ≥ rp ≥ 0.48), while the correlation between RA and other traits was low (0.13 ≥ rp ≥ −0.40). Inbreds with contrasting effects on complexity and architecture traits were observed, suggesting that root complexity and architecture traits are inherited independently. A more comprehensive understanding of the maize root system and the way it interacts with the environment will be useful for defining adaptation to nutrient acquisition and tolerance to stress from drought and high plant densities, critical factors in the yield gains of modern hybrids.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-015-1187-0) contains supplementary material, which is available to authorized users.
Highlights
Plant root systems are responsible for the vital roles of plant anchorage, absorption of water, and assimilation of nutrients (Lynch 1995)
Germplasm In order to assess root traits using germplasm that is more relevant to commercial hybrids, inbreds historically important to commercial breeding programs were identified based on the number of references in Plant Variety Protection certificates and utility patents of proprietary corn inbreds in Mikel and Dudley (2006) and a set of ten Ex-plant variety protection (PVP) inbreds plus B73 and Mo17 were selected for study
Phenotypic means Parental inbreds had smaller mean fractal dimension (FD), fractal abundance (FA), and root angle (RA) trait values (q < 0.001) and narrower trait ranges than F1 hybrids, but the standard deviations for each trait were similar across generations (Table 1)
Summary
Plant root systems are responsible for the vital roles of plant anchorage, absorption of water, and assimilation of nutrients (Lynch 1995). Changes in root system architecture and water acquisition in relation to plant density have shown to be good predictors of the historical elite maize yield (Hammer et al 2009), highlighting the relevance of understanding the factors that influence root growth, development, and response to external factors. There is a scarcity of data on root systems acquired from field experiments, despite the overall importance of the root system for productivity. This is likely a result of the intense labor required to excavate and clean intact root systems on a large scale and the challenge of collecting quantitative data on the numerous fine features of roots within a reasonable time frame. To associate advantageous genetic variation for root characteristics with plant performance, a rapid and accurate means of measuring root traits is needed
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