A study of the physiology and genetics of rapid rooting traits in lettuce (Lactuca sativa)

Roberts, J.M. (2021) A study of the physiology and genetics of rapid rooting traits in lettuce (Lactuca sativa). Doctoral thesis, Harper Adams University.

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Lettuce is usually germinated and grown for a short period in nurseries before planting (transplanted) in the field in the UK and Europe.Plants that are transplanted are more uniform in maturity due to more uniform germination, avoid early environmental stresses and usually mature earlier than direct sown crops. Lettuce transplants need to establish quickly in the field to optimise growth and uniformity and can be exposed to stresses that include mild initial drought,variable soil and environmental conditions and root pruning. These stresses are only likely to be exacerbated with increasing pressures on growers to reduce inputs. Identification of phenotypic and genotypic variation for a “rapid rooting”trait in the lettuce gene pool therefore may enable faster establishment and has the potential to improve the performance of lettuce transplants if integrated into a marker assisted breeding programme for lettuce varieties.The following work optimised a 2D high-throughput assay to screen 14-dayold seedlings of a lettuce diversity fixed foundation set (DFFS)and identified phenotypic variation for key rapid rooting traits that could prove important for future breeding programmes. Phenotypic variation was also observedwithin the DFFS fordeeper rooting potential of lateral rootsandfor root hair traits.The 2D assay was also utilised to identify 16 significant quantitative trait loci (QTL) associated withthe rapid rooting phenotype, of which six were associated with increased primary root growth, three with increased lateral root growth, two were associated with lateral root length density, three with lateral root number density and two with mean lateral root length. Atargeted transcriptomic analysis utilising extreme lines identifiednine candidate genes located under five of the reported QTL for the “rapid rooting” phenotype. The genes coded for proteins involved in various pathways involved with root growth including cell proliferation, cell expansion, cell wall synthesis and ABA synthesis. Thesegenes mayoffer a promising approach for the improvement of lettuce establishment in a commercial breeding programme.The extreme lines were then analysed in a 3D transplant sand assay to assess the effect of altering the root:shoot ratio through controlled root pruninghad on the rapid rooting phenotype and identified that although some ofthelines behaved differently some of the lines maintain a rapid rooting phenotype at transplant maturity and recovered a larger proportion of the root:shootratio compared to the slower rooting lines and commercial controls.

Item Type: Thesis (Doctoral)
Divisions: Agriculture and Environment (from 1.08.20)
Depositing User: Ms Kath Osborn
Date Deposited: 05 Mar 2021 10:51
Last Modified: 22 Jul 2021 11:30
URI: https://hau.repository.guildhe.ac.uk/id/eprint/17657

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