Interaction between Phytophthora cinnamomi zoospores and micro-organisms on non-mycorrhizal and ectomycorrhizal roots of Eucalyptus marginata

On lateritic podzolic soils in Western Australia Eucalyptus calophylla is resistant to Phytophthora cinnamomi whereas Eucalyptus marginata is susceptible and eventually killed by the pathogen. On loam soils both eucalypts are resistant. Possible mechanisms for resistance of E. calophylla in lateritic soil and the inhibitory action of loam soils were investigated. Aseptically raised eucalypt seedlings succumbed to infection in liquid culture tubes. The mechanism of infection was compared by light and electron microscopy which showed similar fungal invasion and penetration into roots of both eucalypt species. Vegetative hyphae initially penetrated intercellularly and proliferated rapidly within cortical and stelar tissue. Intracellular invasion of these tissues occurred 48hr after initial infection through dissolution of the host cell wall. Chlamydospores were formed within a number of cortical cells. Unsuberized roots of mature trees produced aseptically showed reactions to invasion similar to those of the eucalypt seedling roots. Suberized roots were not invaded. The addition of small quantities of lateritic soil to sterile sand so as to introduce soil micro-organisms without altering the chemical and physical status of the sand, and subsequent inoculation of the sand with P.cinnamomi, resulted in a reduction of root damage on both eucalypts when compared with seedlings raised in sterile sand. Roots of E.calophylla were less severely damaged than those of E.marginata. The addition of small quantities of loam soil significantly reduced root damage in seedlings of both species. These results parallel both pot experiments and field observations, and suggest that microorganisms of the rhizosphere may be an important factor in the resistance of E.calophylla to infection, and in the inhibitory effect of loam soil on P.cinnamomi.

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Re-evaluation of Phytophthora Species Isolated During 30 Years of Vegetation Health Surveys in Western Australia Using Molecular Techniques

Plant Disease ◽

10.1094/pdis-93-3-0215 ◽

2009 ◽

Vol 93 (3) ◽

pp. 215-223 ◽

Cited By ~ 55

Author(s):

Treena I. Burgess ◽

Janet L. Webster ◽

Juanita A. Ciampini ◽

Diane White ◽

Giles E. StJ. Hardy ◽

...

Keyword(s):

New Taxa ◽

Western Australia ◽

Dna Sequences ◽

Phytophthora Cinnamomi ◽

Sequence Data ◽

Phytophthora Species ◽

Molecular Techniques ◽

Similar Species ◽

Eucalyptus Marginata ◽

Similar Morphology

For 30 years, large-scale aerial photography has been used to map the extent of Phytophthora dieback disease in native forests in the southwest of Western Australia, with validation of the observations involving routine testing of soil and root samples for the presence of Phytophthora cinnamomi. In addition to P. cinnamomi, six morpho-species have been identified using this technique: P. citricola, P. megasperma, P. cryptogea, P. drechsleri, P. nicotianae, and P. boehmeriae. In recent years, many new Phytophthora species have been described worldwide, often with similar morphology to existing species; thus, as many of the isolates collected in Western Australia have been difficult to identify based on morphology, molecular identification of the morpho-species is required. Based on amplification of the internal transcribed spacer (ITS) region of the rDNA gene, sequence data of more than 230 isolates were compared with those of existing species and undescribed taxa. P. inundata, P. asparagi, P. taxon PgChlamydo, P. taxon personii, and P. taxon niederhauserii were identified based on sequence data. Phylogenetic analysis revealed that nine potentially new and undescribed taxa can be distinguished. Several of the new taxa are morphologically indistinguishable from species such as P. citricola, P. drechsleri, and P. megasperma. In some cases, the new taxa are closely related to species with similar morphology (e.g., P.sp.4 and P. citricola). However, the DNA sequences of other new taxa such as P.sp.3 and P.sp.9 show that they are not closely related to morphologically similar species P. drechsleri and P. megasperma, respectively. Most of the new taxa have been associated with dying Banksia spp., while P.sp.2 and P.sp.4 have also been isolated from dying Eucalyptus marginata (jarrah). Some taxa (P.sp.3, 6, and 7) appear to have limited distribution, while others like P.sp.4 are widespread.

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Variation in seasonal population fluctuations of Phytophthora cinnamomi within and between infected Eucalyptus marginata sites of southwestern Australia

Forest Ecology and Management ◽

10.1016/0378-1127(87)90044-2 ◽

1987 ◽

Vol 21 (3-4) ◽

pp. 209-230 ◽

Cited By ~ 21

Author(s):

B.L. Shearer ◽

S.R. Shea

Keyword(s):

Phytophthora Cinnamomi ◽

Population Fluctuations ◽

Eucalyptus Marginata ◽

Southwestern Australia ◽

Seasonal Population

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Relative importance of site, weather and Phytophthora cinnamomi in the decline and death of Eucalyptus marginata – jarrah dieback investigations in the 1970s to 1990s

Australasian Plant Pathology ◽

10.1007/s13313-018-0558-8 ◽

2018 ◽

Vol 47 (3) ◽

pp. 245-257 ◽

Cited By ~ 5

Author(s):

E. M. Davison

Keyword(s):

Phytophthora Cinnamomi ◽

Relative Importance ◽

Eucalyptus Marginata

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Pathogenic Variability in Australian Isolates of Phytophthora cinnamomi

Australian Journal of Botany ◽

10.1071/bt9930721 ◽

1993 ◽

Vol 41 (6) ◽

pp. 721 ◽

Cited By ~ 25

Author(s):

MJ Dudzinski ◽

KM Old ◽

RJ Gibbs

Keyword(s):

Phytophthora Cinnamomi ◽

Growth Period ◽

Species Variation ◽

Eucalyptus Marginata ◽

Disease Symptoms ◽

Horticultural Crops ◽

Damage Reduction ◽

Single Clone ◽

Pathogenic Variability ◽

Stable Characteristic

Forty-two isolates of Phytophthora cinnamomi were obtained from native vegetation and horticultural crops within Australia. They represented a broad spectrum of geographical and host origins, both mating types, and all identified Australian isozyme genotypes. All isolates were tested for their pathogenicity to a single clone of Eucalyptus marginata by inoculation of soil in which plants were growing. Differences in pathogenicity were expressed as extent of root damage, reduction of plant growth, period to first visible disease symptoms and time to plant death. Significant variation between isolates was detected. Pathogenicity was unrelated to mating type and isozyme properties. A subset of these 42 isolates encompassing a range of virulence gave generally consistent rankings for pathogenicity variates when re-inoculated twice into plants derived from the original clone. This suggests that pathogenicity is a relatively stable characteristic. Detection of differences in susceptibility to P. cinnamomi between three selected E. marginata. clones was influenced by the pathogenicity of isolates. Only the more pathogenic isolates were useful in this regard. Seedling stems of five eucalypt species were inoculated with virulent and less virulent isolates of P. cinnamomi. This method detected variation in both pathogenicity in the fungus and susceptibility in the host species. Variation in pathogenicity within Australian populations of P. cinnamomi should be taken into account by the choice of isolates of proven virulence when selecting for resistance in trees and other woody hosts.

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Distribution of Phytophthora cinnamomi in the northern jarrah (Eucalyptus marginata) forest of Western Australia in relation to dieback age and topography

Australian Journal of Botany ◽

10.1071/bt01040 ◽

2002 ◽

Vol 50 (1) ◽

pp. 107 ◽

Cited By ~ 21

Author(s):

K. L. McDougall ◽

G. E. St J. Hardy ◽

R. J. Hobbs

Keyword(s):

Spatial Distribution ◽

Western Australia ◽

Aerial Photography ◽

Phytophthora Cinnamomi ◽

Ex Situ ◽

Patchy Distribution ◽

Jarrah Forest ◽

Eucalyptus Marginata ◽

Almost All

The spatial distribution of Phytophthora cinnamomi Rands at seven dieback sites in the jarrah (Eucalyptus marginata Donn. ex Smith) forest of Western Australia was determined by the following two baiting techniques: in situ baiting with live Banksia grandis Willd. seedlings and ex situ baiting of sampled soil and root material. Four areas within each site were sampled, reflecting dieback age and position in the landscape. Approximate dieback ages of 50, 20 and 5 years were determined by aerial photography. The 50-year-old age class was divided into wet valley floor and dry gravelly slope. Phytophthora cinnamomi was recovered most frequently from the 5-year-old (dieback fronts) and wet 50-year-old areas by both baiting techniques. It was recovered from more than twice as many areas and about five times as many samples when in situ B. grandis baits were used compared with ex situ soil and root baiting. Almost all recoveries from in situ baits were made between October and December. From both methods, it appears that P. cinnamomi has a patchy distribution within dieback sites in the northern jarrah forest. It is easily detected only on dieback fronts and wet valley floors. On dry gravelly sites affected 20 years or more ago, P. cinnamomi is rare and may even be absent at some sites. This makes confident detection of the pathogen difficult. In situ baiting at least allows a temporal component to the sampling and will be a useful method of detection in areas where P. cinnamomi is rare or transient.

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Site and Seasonal Effects on Susceptibility of Eucalyptus marginata to Phytophthora cinnamomi

Australian Journal of Botany ◽

10.1071/bt9890481 ◽

1989 ◽

Vol 37 (6) ◽

pp. 481 ◽

Cited By ~ 16

Author(s):

JT Tippett ◽

JF Mcgrath ◽

TC Hill

Keyword(s):

Phytophthora Cinnamomi ◽

Water Status ◽

Fungal Growth ◽

Soil Nutrient ◽

Nutrient Status ◽

Seasonal Effects ◽

Soluble Carbohydrate ◽

Eucalyptus Marginata ◽

Relative Water ◽

Stem Lesions

Susceptibility of Eucalyptus marginata stems and roots to invasion by Phytophthora cinnamomi was compared at four sites in the northern jarrah forest and reasons for differences in tree susceptibility were sought. The sites were located in both the low (750 mm year -I ) and high (1 100 mm year -1) rainfall zones and differed in understorey composition and soil nutrient status. Stems were inoculated at monthly intervals between October 1983 and April 1984. Measurement of stem lesions induced by inoculation showed that rate of fungal growth in trees at all sites generally increased during the October-December (1983) period. During February and March (1984) there was a large difference in the susceptibility of stems and roots in low-rainfall zone sites compared with those in high-rainfall zone sites. Roots inoculated during February at three of the four sites showed the same relative susceptibilities as stems inoculated one week later. Mean relative water contents (RWC) of the phloem (inner bark) were used to compare the water status of the saplings at the four sites and the observed inhibition of the fungus in the sapling stems and roots at the driest sites, coincided with the months when phloem RWC values were at their lowest. Phloem was also sampled from pole-sized trees at the four sites and seasonal changes in RWC values, soluble carbohydrate concentrations and phenols were monitored for 12 months. Soluble carbohydrate concentrations in the phloem of some of the saplings inoculated at each site were also determined. Concentrations of carbohydrates and phenols did change seasonally and differed between sites but no evidence was found to suggest that they had a direct effect on fungal growth.

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Quantification of the susceptibility of the native flora of the South-West Botanical Province, Western Australia, to Phytophthora cinnamomi

Australian Journal of Botany ◽

10.1071/bt03131 ◽

2004 ◽

Vol 52 (4) ◽

pp. 435 ◽

Cited By ~ 112

Author(s):

B. L. Shearer ◽

C. E. Crane ◽

A. Cochrane

Keyword(s):

Western Australia ◽

National Park ◽

Phytophthora Cinnamomi ◽

Natural Environments ◽

The South ◽

Irreversible Damage ◽

Eucalyptus Marginata ◽

Native Flora ◽

South West ◽

Wide Range

This study compares, for the first time, variation in estimates of susceptibility of native flora to Phytophthora cinnamomi Rands among four databases and proposes an estimate of the proportion of the flora of the South-West Botanical Province of Western Australia that is susceptible to the pathogen. Estimates of the susceptibility of south-western native flora to P. cinnamomi infection were obtained from databases for Banksia woodland of the Swan Coastal Plain, jarrah (Eucalyptus marginata Donn. ex Smith) forest, the Stirling Range National Park and Rare and Threatened Flora of Western Australia. For the woodland, forest and national park databases, hosts were naturally infected in uncontrolled diverse natural environments. In contrast, threatened flora were artificially inoculated in a shadehouse environment. Considerable variation occurred within taxonomic units, making occurrence within family and genus poor predictors of species susceptibility. Identification of intra-specific resistance suggests that P. cinnamomi could be having a strong selection pressure on some threatened flora at infested sites and the populations could shift to more resistant types. Similar estimates of the proportion of species susceptible to P. cinnamomi among the databases from the wide range of environments suggests that a realistic estimate of species susceptibility to P. cinnamomi infection in the south-western region has been obtained. The mean of 40% susceptible and 14% highly susceptible equates to 2284 and 800 species of the 5710 described plant species in the South-West Botanical Province susceptible and highly susceptible to P. cinnamomi, respectively. Such estimates are important for determining the cost of disease to conservation values and for prioritising disease importance and research priorities. P. cinnamomi in south-western Australia is an unparalleled example of an introduced pathogen with a wide host range causing immense irreversible damage to unique, diverse but mainly susceptible plant communities.

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