Engineering Allium White Rot Disease Resistance in Allium Species and Tobacco Model Species

Type of content
Theses / Dissertations
Publisher's DOI/URI
Thesis discipline
Microbiology
Degree name
Master of Science
Publisher
University of Canterbury. School of Biological Sciences
Journal Title
Journal ISSN
Volume Title
Language
Date
2009
Authors
Glue, Joshua Barnaby
Abstract

Allium white rot (AWR) is a soilborne disease that seriously damages commercial cultivation of onion (Allium cepa) and garlic (Allium sativum) crops. The disease has been found everywhere onions are cultivated and at present no system of control has been found that fully prevents the occurrence of the disease. The fungus responsible for the disease, Sclerotium cepivorum, uses oxalic acid to kill Allium bulb and root tissue in growing onion and garlic plants. Research suggests recombinant oxalate oxidase and oxalate decarboxylase enzymes may be able to degrade this acid and confer resistance against pathogens that rely on it, such as Sm. cepivorum or Sclerotinia sclerotiorum.

To test the efficacy of these enzymes against white rot pathogens, three transgenes for wheat oxalate oxidase, barley oxalate oxidase and Flammulina oxalate decarboxylase were transformed into onions and garlic by Agrobacterium-mediated transformation. Allium species are highly recalcitrant to transformation, so these three transgenes were also transformed into tobacco to provide fast-recovering, easy to test transformants to assess the efficacy of the transgenes. Transformed garlic and tobacco lines were analysed to assess the integration and expression of the transgenes, then challenged with Sm. cepivorum or Sa. sclerotiorum, respectively, to assess the bioactivity of recombinant wheat oxalate oxidase, barley oxalate oxidase, and Flammulina oxalate decarboxylase against oxalic acid-dependent pathogens.

Results show that one line of tobacco expressing the Flammulina oxalate decarboxylase enzyme was found to be consistently resistant to Sclerotinia sclerotiorum. Garlic lines transformed with this transgene failed to display stable transgene expression or disease resistance, possibly due to silencing of the transgene in recovered transformant tissue.

Description
Citation
Keywords
Allium, oxalic acid, Sclerotium cepivorum, Sclerotinia sclerotiorum, oxalate oxidase, oxalate decarboxylase, Allium genetic transformation, disease resistance
Ngā upoko tukutuku/Māori subject headings
ANZSRC fields of research
Rights
Copyright Joshua Barnaby Glue