Transformation of 'Thielaviopsis basicola' to study host-pathogen interactions

Abstract

'Thielaviopsis basicola', a filamentous fungus, is a soil-borne plant pathogen belonging to the teleomorphic genus 'Ceratocystis' (perithecial ascomycete). Different strains are capable of attacking a wide range of host plants causing black root rot, a seedling disease. Control strategies based on cultural practices, biocontrol agents, chemical fungicides, and genetically determined host resistance have not yet solved the issue of the loss of yield of agricultural crops. The main aim of this project was to investigate the molecular aspects of host-pathogen interactions, generate new knowledge and make progress towards the development of new control strategies for black root rot. For 'T. basicola' to cause black root rot, it germinates in soil forming a germ tube that elongates to reach the plant roots, attaches to the root surface and penetrates into the root hairs or epidermal cells. It is possible that signalling mechanisms may be required at different stages of the infection process for its progress. 'In vitro' pathogenicity and water agar assays were developed in order to understand and appreciate the ability of 'T. basicola' to perceive signals and respond by germination and/or directed growth towards various plants and in order to analyse the susceptibility of various plants, 'in vitro' pathogenicity and water agar assays were developed. The results provided evidence that exudates released by roots of host and non-host plants were responsible for hyphal directional growth towards plant roots. There was little evidence to suggest that a host-specific stimulus caused hyphal directional growth. There was also little evidence to suggest that a correlation existed between hyphal directional growth towards host plants and disease severity caused by 'T. basicola' isolates. Isolates that showed a strong hyphal directional growth response towards a particular susceptible plant did not necessarily cause disease. Strains of 'T. basicola' isolated from particular hosts may exhibit stronger growth direction and/or pathogenicity towards other hosts.