Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Biology

Program Name/Specialization

Integrative Biology

Faculty/School

Faculty of Science

First Advisor

Dr. Mihai Costea, Dr. Frederique Guinel

Advisor Role

Co-supervisor

Abstract

Cuscuta (dodder), the only parasitic genus of Convolvulaceae family, is a significant plant from ecological, economical, and conservational point of views. The genus consists of c. 200 described species with wide ranges of ecological distributions. Cuscuta spp. are categorized as stem parasitic plants with reduced (or lost) photosynthesis-related genes. The filamentous coiled embryo, embedded in the endosperm, lacks cotyledons and is covered with a multiple-layered seed coat. The seedlings carry a vestigial root-like organ which is not considered a ‘true’ functional root. Members of the genus differ in their germination rate and seedling survival. It is known that seed germination, as a vital stage for seedling establishment, is influenced by the impermeable seed coat in most Cuscuta species. However, anatomical data are still lacking; for example, it is unknown how seed coats of Cuscuta species differ from one another, and if the differences (if any) affect the germination rates. In the seedling stage, Cuscuta lives for a short period of time if the plant cannot attach to a proper host(s). The seedling lifespan varies widely among Cuscuta species; however, the factors causing the variations have not received much attention. Thus, the aims of this study are: 1) to examine the structure of Cuscuta seed coats in relation to the germination success using three Cuscuta species, 2) to study the capability of Cuscuta vestigial root to absorb water and nutrients, and 3) to investigate factors affecting seedling growth and longevity, including mycorrhizal association, in two Cuscuta species. To achieve these goals, various microscopic techniques were employed to examine the structure of the seed coat. Furthermore, the interaction of two mycorrhizal fungal species with the roots and the effects of fungal colonisations on seedling growth and survival of two Cuscuta species were studied. Moreover, morphological, structural and absorptive capabilities of the root were investigated. Structural analysis of the seed coats suggested that palisade layers and the overall seed coat thickness likely have significant effects on the germination rate. The absorptive capabilities and mycorrhizal associations of the Cuscuta seedling roots led me to consider the vestigial root-like organ of the Cuscuta seedlings as a ‘true’ root although it is an ephemeral organ. I noted that Cuscuta species interact differently with the fungal species causing dissimilarity in the growth and longevity of their seedlings. This suggests that the fungal specificity may play a role in the ecological distributions of Cuscuta species. The work presented in this thesis is significant because it brings to light a relationship between species survival and ecological distribution.

Convocation Year

2014

Convocation Season

Fall

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