Development of a Rhizosheath Selection Tool for screening perennial ryegrass (Lolium perenne L.) for reduced root competition against white clover (Trifolium repens L.) for soil phosphorus
Yeates, R. M. (2018). Development of a Rhizosheath Selection Tool for screening perennial ryegrass (Lolium perenne L.) for reduced root competition against white clover (Trifolium repens L.) for soil phosphorus (Thesis, Master of Science (Research) (MSc(Research))). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/12078
Permanent Research Commons link: https://hdl.handle.net/10289/12078
Perennial ryegrass (Lolium perenne L.) outcompetes white clover (Trifolium repens L.) for soil phosphorus [P], resulting in higher P fertiliser rates to overcome the competition. Perennial ryegrass has long, dense root hairs compared to white clover, which increase the root contact with soil (soil exploration) and root surface area for P uptake. This study was conducted to test whether the selection of perennial ryegrass with reduced root hair length and density would reduce root competition for P with no detrimental effect on the perennial ryegrass growth. A Rhizosheath Selection Tool [RST] was developed to select ryegrass populations with contrasting root hair length and density. The RST protocol used rhizosheath traits (the width and coverage of soil adhered to the extracted root system) along with the total seedling weight to select two distinct ryegrass populations. The low rhizosheath population had shorter, sparser root hairs on seminal roots and sparser root hairs on adventitious roots than the high rhizosheath population. The two populations were then grown at five soil P levels in a glasshouse experiment and demonstrated that the rhizosheath trait selection had no detrimental effect on growth. There were no significant differences between the two population’s dry weight (g) and P concentration (mg P g-1 dry weight). However there was evidence to indicate that the high rhizosheath population was sometimes more efficient at P uptake with a larger total P content (mg P). The two perennial ryegrass populations were then grown with companion white clover in Olsen P 12 and 19 mg L⁻¹ soil with partitions separating the shoot systems to avoid shoot competition for light. The low rhizosheath population had reduced root competition with the companion white clover. In Olsen P 12 mg L⁻¹ soil, more P was partitioned to the white clover than the ryegrass, measured by total P content (mg P), and achieved a greater dry weight (g) than when grown with the HRS ryegrass. In Olsen P 19 mg L⁻¹ soil there was no rhizosheath selection effect on white clover growth, possibly because of the reduced need for soil exploration by roots under the higher soil P availability. The findings from this study confirmed that the RST for the selection of a perennial ryegrass population with a reduced capacity for root competition against white clover for soil P is effective. Furthermore, the RST selection had no detrimental effect to the ryegrass growth. This research highlights the importance of root traits in forage plant breeding, and the potential environmental and economic benefits a low rhizosheath perennial ryegrass could have in New Zealand’s pastoral farming system.
The University of Waikato
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