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Title: Evolutionary dynamics of domestication : the case of Brassica rapa
Author: Bell, P. E. C.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2006
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The presence of three B. rapa forms in the UK provides an opportunity for a unique study of the relationships between cultivated B. rapa, and weedy and wild derived from them - the escape from cultivation. A range of morphological characters have been studied along with the DNA markers, AFLP and microsatellites, using the same plant material. Morphological characters discriminated between wild, weedy and cultivated forms of B. rapa. Within the cultivated group, the morphological analysis separates B. rapa var oleifera winter and spring turnip oil seed rape varieties. B. rapa var rapa stubble turnip varieties are separated from root turnip. Based on morphological analysis wild and weedy groups are differentiated, but this is not supported by AFLP analysis. AFLPs, as neutral markers, reflect the agricultural histories of B. rapa cultivars. All B. rapa var. rapa and var. oleifera cultivars clustered together in principal co-ordinate plots, although two accessions of vars. rapa clustered with wild and weedy forms (traditional cultivars, ‘Hardy Green Round’ and ‘Lincolnshire Red Globe’). Significant levels of genetic variation was observed in all B. rapa accessions. Genetic evidence indicates that weedy B. rapa is derived from wild plants not directly from cultivars. The microsatellite analysis indicated significant distinctions in allele frequency between wild, weedy and cultivated forms. The population structure of cultivated and weedy B. rapa was distinct from the wild group, with much enhanced homozygosity. Inbreeding and founder effects may be important factors here. Some plants of wild B. rapa growing adjacent to B. napus show intermediate DNA and morphological phenotypes. This indicates natural hybridisation and backcrossing.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available