Survival of different life stages of phytophthora cinnamomi (RANDS) in soil and plant roots under mine site conditions

Gyeltshen, Jamba (2018) Survival of different life stages of phytophthora cinnamomi (RANDS) in soil and plant roots under mine site conditions. PhD thesis, Murdoch University.

Abstract

Phytophthora cinnamomi (Rands) is a soil and water-borne plant pathogen, associated with a devastating dieback disease in the jarrah (Eucalyptus marginata) forest, in Western Australia. As the forest is an active site for extensive open-cut bauxite mining, it is a challenge to prevent the potential spread of P. cinnamomi. Despite years of research, we have not fully understood how P. cinnamomi survives the long, hot and dry Mediterranean summer in the jarrah forest ecosystem, particularly under mine site conditions where surface temperatures periodically reach 60 ºC.

This study looked at the life span of oospores, chlamydospores and encysted zoospores under conditions typical of the mine sites. In particular, it compared the effect of dry and moist soil conditions on survival of oospores and chlamydospores. The study also examined the effects of exogenous materials (smoke water, fish emulsion, and the fungicides, ridomil and furalaxyl) that are known to have stimulatory or inhibitory effects on growth. These were shown not to have any significant impact on the survival structures.

The findings indicate that oospores of P. cinnamomi survive in the soil for less than one year irrespective of soil moisture conditions, while chlamydospores survive for less than 12 weeks under similar conditions. Encysted zoospores under submerged conditions (similar to those in drainage sumps along haul roads) did not survive beyond one week.

The effect of varying moisture levels was examined with oospores of a closely related species (P. multivora) which is associated with the dieback disease complex. At matric potentials between -1 kPa and -6 MPa, there was a clear decline in oospore viability, and at -6 MPa, which is the level of dryness typically experienced during the hot dry summers, oospore viability was reduced to 66% after 60 days.

The possible role of non-susceptible or tolerant host plants growing on topsoil stockpiles on pathogen survival was investigated to determine how plants contribute to the long-term survival of the pathogen. Meta-barcoding and high throughput sequencing detected P. cinnamomi on 16 of the 20 plant species assessed. Unexpectedly, the technique revealed the putative presence of 24 other Phytophthora species, thereby raising more questions on the role of these plants in the Phytophthora disease cycle. Based on the findings, this study recommends that the stockpiles be maintained in situ and plant-free for at least 2-3 years to minimize the risk of spreading the pathogen and permanently removing the source of inoculum.

Item Type:	Thesis (PhD)
Murdoch Affiliation(s):	School of Veterinary and Life Sciences
Supervisor(s):	Hardy, Giles, Burgess, Treena and Dunstan, Bill
URI:	http://researchrepository.murdoch.edu.au/id/eprint/40834

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