Verticillium wilt in Australian cotton: Examining the relationship between Australian Verticillium dahliae isolates and virulence

Field	Value	Language
dc.contributor.author	Dadd-Daigle, Pearl S.
dc.date.accessioned	2022-12-11T23:33:43Z
dc.date.available	2022-12-11T23:33:43Z
dc.date.issued	2022
dc.identifier.uri	http://hdl.handle.net/10453/164288
dc.description	University of Technology Sydney. Faculty of Science.	en_US.UTF-8
dc.description.abstract	Verticillium wilt, caused by the soil-borne phytopathogen Verticillium dahliae, affects many agriculturally important crops around the world, and, in Australia, the billion dollar cotton industry is increasingly impacted. Verticillium dahliae defoliating VCG1A is reported to cause severe damage to cotton internationally, while non-defoliating VCG2A is responsible for only mild to moderate disease symptoms. In Australian cotton however, the non-defoliating VCG2A is causing more severe damage to crops in the field than the defoliating VCG1A. A selection of isolates taken from the New South Wales (NSW) Department of Primary Industries Verticillium collection were used to infect cotton plants in controlled greenhouse conditions. Analysis revealed that although disease progression is slower in plants infected with non-defoliating VCG2A isolates, both Australian defoliating VCG1A and non-defoliating VCG2A are able to kill cotton plants in glasshouse trials. Cotton variety had minimal impact on disease outcomes. This was the first confirmed report of an Australian non-defoliating VCG2A causing plant mortality in cotton plants outside of the field. Eighty-four isolates from the NSW Department of Primary Industries Verticillium historical collection were further analysed using InterSequence Simple Repeats (ISSR) to produce a phylogenetic tree. The isolates clustered into three main groups. These groups were labelled “Defoliating-like”, “Non-defoliating”, and “Defoliating”, respectively. Further glasshouse trials to examine the virulence of isolates in each group confirmed that the virulent VCG2A isolates all fell within the “Defoliating-like” group, the virulent VCG1A isolates within the “Defoliating” group, and all non-virulent isolates in the “Non-defoliating” group. The inclusion of American V. dahliae defoliating VCG1A isolates and eight Israeli isolates of varying VCG into the ISSR study revealed that the Australian isolates appear to cluster separately and suggests that Australian V. dahliae isolates could be unique to Australia. To further examine the differences between Australian and international defoliating VCG1A V. dahliae, four VCG1A V. dahliae isolates were DNA sequenced using both Nanopore Minion and Illumina sequencing platforms to produce whole genomes. Isolates were analysed with 13 publicly available V. dahliae isolates using phylosift, and gene content examined using ProgressiveMauve. The comparisons found minimal differences between the four Australian isolates, but when compared with the other 13, they appear more genetically distant. Additionally, Australian VCG1A isolates lack a set of genes identified as being in involved in defoliation of cotton plants. This work highlights, for the first time, genetic differences between Australian and international defoliating VCG1A V. dahliae.	en_US.UTF-8
dc.format	Thesis (PhD)
dc.language.iso	en_US	en_US.UTF-8
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/164288/2/02whole.pdf
dc.rights	The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
dc.rights	au.edu.uts.lib/ppc
dc.rights	info:eu-repo/semantics/openAccess
dc.title	Verticillium wilt in Australian cotton: Examining the relationship between Australian Verticillium dahliae isolates and virulence	en_US.UTF-8
dc.type	Thesis
utslib.copyright.status	open_access	*

Abstract:

Verticillium wilt, caused by the soil-borne phytopathogen Verticillium dahliae, affects many agriculturally important crops around the world, and, in Australia, the billion dollar cotton industry is increasingly impacted. Verticillium dahliae defoliating VCG1A is reported to cause severe damage to cotton internationally, while non-defoliating VCG2A is responsible for only mild to moderate disease symptoms. In Australian cotton however, the non-defoliating VCG2A is causing more severe damage to crops in the field than the defoliating VCG1A. A selection of isolates taken from the New South Wales (NSW) Department of Primary Industries Verticillium collection were used to infect cotton plants in controlled greenhouse conditions. Analysis revealed that although disease progression is slower in plants infected with non-defoliating VCG2A isolates, both Australian defoliating VCG1A and non-defoliating VCG2A are able to kill cotton plants in glasshouse trials. Cotton variety had minimal impact on disease outcomes. This was the first confirmed report of an Australian non-defoliating VCG2A causing plant mortality in cotton plants outside of the field. Eighty-four isolates from the NSW Department of Primary Industries Verticillium historical collection were further analysed using InterSequence Simple Repeats (ISSR) to produce a phylogenetic tree. The isolates clustered into three main groups. These groups were labelled “Defoliating-like”, “Non-defoliating”, and “Defoliating”, respectively. Further glasshouse trials to examine the virulence of isolates in each group confirmed that the virulent VCG2A isolates all fell within the “Defoliating-like” group, the virulent VCG1A isolates within the “Defoliating” group, and all non-virulent isolates in the “Non-defoliating” group. The inclusion of American V. dahliae defoliating VCG1A isolates and eight Israeli isolates of varying VCG into the ISSR study revealed that the Australian isolates appear to cluster separately and suggests that Australian V. dahliae isolates could be unique to Australia. To further examine the differences between Australian and international defoliating VCG1A V. dahliae, four VCG1A V. dahliae isolates were DNA sequenced using both Nanopore Minion and Illumina sequencing platforms to produce whole genomes. Isolates were analysed with 13 publicly available V. dahliae isolates using phylosift, and gene content examined using ProgressiveMauve. The comparisons found minimal differences between the four Australian isolates, but when compared with the other 13, they appear more genetically distant. Additionally, Australian VCG1A isolates lack a set of genes identified as being in involved in defoliation of cotton plants. This work highlights, for the first time, genetic differences between Australian and international defoliating VCG1A V. dahliae.

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