The potential for biological control of Zantedeschia aethiopica: A survey of south-western Australia for pathogens of this noxious weed

Maxwell, Aaron (1997) The potential for biological control of Zantedeschia aethiopica: A survey of south-western Australia for pathogens of this noxious weed. Honours thesis, Murdoch University.

Abstract

Zantedeshia aethiopica (arum lily) is a noxious weed in south-western Australia. Herbicides are ineffective in controlling it in native forest and bushland. Biological control of weeds using indigenous or 'naturalised' plant pathogens in an inundative or 'mycoherbicide' strategy is an effective, host specific method of weed control. The work in this thesis tested the hypothesis that there are pathogens of Z. aethiopica present in the weed population of Z. aethiopica in south-western Australia. The objective of the study was to provide the groundwork to establish a potential bio-control programme for Z. aethiopica.

Surveys were conducted for fungal, bacterial and nematode pathogens of Z. aethiopica over three geographic regions in south-western Australia: Perth metropolitan area; Garden Island nature reserve; and the Buselton-Augusta region. The diversity in fungi isolated varied amongst the three regions, with the greatest diversity of fungi being recovered from the Busselton-Augusta region of the study and the least diversity from the Garden Island region. Possible explanations for this variation are differences in rainfall, soil organics and soil pH.

A total of 782 isolates werer recovered from diseased roots and rhizomes of Z. aethiopica. Of these the fungal genera most commonly isolated from root or I rhizome rots were Fusarium, Pythium, Rhizoctonia and Alternaria species. These genera are all potential plant pathogens which have been isolated from z. aethiopica by workers world-wide. The most commonly isolated fungal species were Fusarium solani and Fusarium oxysporum. A frequently isolated Pythium sp. was identified as P. coloratum. This is a new host pathogen association. The most commonly occurring fungi associated with leaf lesions were Phoma species. It is unlikely that the Phoma spp. isolated were Phoma zantedeschia as the isolated organisms failed to fit the original description of this species which has clusters of of multi-septate chlamydospores. This is significant as it indicates that P. zantedeschia, a pathogen of Z. aethiopica in a number of countries throughout the world, is unlikely to be present in southwestern Australia. Another serious pathogen isolated from Z. aethiopica both overseas and in New South Wales which was not isolated in this study is Phytophthora richardiae.

Bacteria were associated with soft rots of rhizomes. Out of 50 bacterial isolates, nine of the most commonly occurring forms were examined in detail. Five were identified as Pseudomonas spp. and four as Erwinia species. These 9 isolates were tested for pathogenicity toward Z. aethiopica by infecting roots of Z. aethiopica grown in an aeroponics system. There was some indication that one of the Erwinia isolates may have been pathogenic toward Z. aethiopica. The differences were not significant (p>O.OS) but it is postulated that this is because of the high standard error, which could have been compensated for by increasing the number of replicates per treatment.

Fusarium oxysporum and Fusarium solani isolated from rhizome rots of z. aethiopica were also tested for pathogenicity toward Z. aethiopica in an aeroponics system. Lesion development was greater in response to inoculation with Fusarium isolates Foxl and Fs2 than in the non-inoculated controls, particularly in wounded treatments. The nematode Meloidogyne javanica was identified as the causal agent of galled roots observed on Z. aethiopica at 2 sites. This is a new host pathogen association. Meloidogyne javanica has a very broad host range and hence is not suitable as a biological control agent against Z. aethiopica. The diverse range of pathogenic genera isolated from Z. aethiopica gives reason for some optimism in the search for a bio-control agent to control the noxious weed Z. aethiopica. The existence of host specific pathovars of Fusarium oxysporum and Alternaria spp., which have been use in the biocontrol of weeds, offer avenues for further research into biocontrol of Z. aethiopica.

Item Type:	Thesis (Honours)
Murdoch Affiliation(s):	School of Biological and Environmental Sciences
Notes:	A digital copy of this thesis is not available. Your library can request a copy from Murdoch University Library via Document Delivery. A fee applies to this service.
Supervisor(s):	Hardy, Giles and Scott, J.
URI:	http://researchrepository.murdoch.edu.au/id/eprint/32812

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