Distribution of Phytophthora cinnamomi-Supprcssive Soil in Nature

Phytophthora cinnamomi-suppressivc soils were found to be widely distributed in nature. About 40 % of soil samples collected from locations with different vegetation, soil type or elevation throughout the island of Hawaii were suppressive to chlamydospore germination of Phytophthora cinnamomi. Soil samples collected from the same general areas varied greatly in degree of suppressive-ness to P. cinnamomi, ranging from conducive to strongly suppressive. Among the 155 soil samples tested, those with pH close to 4 or 8 tend to be more suppressive to P. cinnamomi than those with pH close to 6.     

Interaction of vesicular arbuscular mycorrhiza with root knot nematodes in tomato

Summary The interaction between the VA mycorrhizal fungus,Glomus fasciculatus and the root-knot nematodes,Meloidogyne incognita andM. javanica, and their effects on the growth and phosphorus nutrition of tomato was studied in a red sandy loam soil of pH 6.0. Inoculation of tomato roots with root-knot nematodes enhanced infection and spore production byG. fasciculatus. Inoculation of tomato plants withG. fasciculatus significantly reduced the number and size of the root-knot galls produced byM. incognita andM. javanica. Inoculation withG. fasciculatus although improved plant growth and its total phosphorus content compared to the uninoculated plants, the difference were not statistically significant.     

Containment and spot eradication of a highly destructive,invasive plant pathogen (<Emphasis Type="Italic">Phytophthora cinnamomi</Emphasis>) in natural ecosystems

The invasive plant pathogen Phytophthora cinnamomi (Stramenopila, Oomycota) has been introduced into 15 of the 25 global biodiversity hotspots, threatening susceptible rare flora and degrading plant communities with severe consequences for fauna. We developed protocols to contain or eradicate P. cinnamomi from spot infestations in threatened ecosystems based on two assumptions: in the absence of living hosts, P. cinnamomi is a weakly competitive saprotroph; and in the ecosystems we treated, the transmission of the pathogen occurs mainly by root-to-root contact. At two P. cinnamomi-infested sites differing in climate and vegetation types, we applied increasingly robust treatments including vegetation (host) destruction, fungicides, fumigation and physical root barriers. P. cinnamomi was not recovered at three assessments of treated plots 6–9 months after treatments. Given the high rates of recovery of P. cinnamomi from untreated infested soil and the sampling frequency, the probability of failing to detect P. cinnamomi in treated soil was <0.0003. The methods described have application in containing large infestations, eradicating small infestations and protecting remnant populations of threatened species.     

Studies in tetrapartite symbioses

Alnus incana seedlings were successfully inoculated with an endomycorrhizal fungus (Glomus fasciculatus), an ectomycorrhizal fungus (Paxillus involutus) and an isolate ofFrankia (ACN1) simultaneously. The effects of the inoculation treatments on the growth performance of the seedlings were evaluated under controlled conditions.The overall growth performance of the seedlings inoculated with the three organisms was better than those inoculated withFrankia, G. fasciculatus andP. involutus individually or withFrankia+G. fasciculatus andFrankia+P. involutus combinations. The highest growth performance and mycorrhizal infection occurred when the seedlings were inoculated simultaneously withFrankia+G. fasciculatus+P. involutus.     

Mechanisms of salt tolerance in transgenic Arabidopsis thaliana constitutively overexpressing the tomato 14-3-3 protein TFT7

A hydroponics experiment was conducted to investigate the effects of iron plaque on root surfaces with respect to selenite uptake and translocation within the seedlings of two cultivars of rice (Oryza sativa L. cv Xiushui48 and Bing9652). Different amounts of iron plaque were formed by adding 0, 10, 30, 50, 70 mg Fe l⁻¹ in the nutrient solution. After 24 h of growth, the amount of iron plaque was positively correlated with the Fe²⁺ addition to the nutrient solution. These concentrations of Fe, inducing plaque, had no significant effect on the shoot and root growth of rice plants in 50 μg Se l⁻¹ nutrient solution. The amount of Se accumulated in iron plaque was positively correlated to the amount of iron plaque. Increasing iron plaque decreased the selenium concentration in shoots and in roots. At the same time, the translocation of Se from roots to shoots was reduced with increasing amounts of iron plaque. At both the shorter and longer exposure times, the ratio of root- to-shoot selenium was higher than in the controls. More Se stayed in the roots at the longer exposure time than at the shorter time. The concentration of selenium in the xylem sap was sharply decreased with increasing amount of iron plaque on the rice roots. The DCB (dithionite-citrate-bicarbonate)-extracted Se was up to 89.9–91.1% of the total Se when roots with iron plaque (Fe 70) were incubated in 50 μg Se l⁻¹ solution for 30 min. This DCB-extracted Se, however, accounted for only 21.9–28.7% of total Se when roots with iron plaque were incubated in the same solution for 3 days. Se adsorbed in iron plaque can be desorbed by low-molecular-weight organic acids, similar to the desorption of Se from ferrihydrite. These results suggest that iron plaque might act as a ‘buffer’ for Se in the rhizosphere.     

Bioclimatic analysis of the distribution of damage to native plants in Tasmania by Phytophthora cinnamomi

Climatic profiles were generated by the computer program BIOCLIM for three sets of sites in native vegetation in Tasmania: (i) 308 sites at which Phytophthora cinnamomi was isolated from diseased plants Pc+ ive; (ii) 322 sites in healthy plant communities from which P. cinnamomi could not be recovered Pc?ive; and (iii) 801 sites representing the climatic range across Tasmania. A discriminatory analysis comparing the first and third sets indicated that seven of the 16 climatic indices available for analysis were good discriminators of the distribution of damage by P. cinnamomi. The analysis suggests that damage to native vegetation due to P. cinnamomi is unlikely on sites where annual mean temperature does not exceed 7.5°C or annual mean rainfall is < 600 mm. Two maps were produced to indicate those areas of Tasmania that have climates suited to damaging interaction between P. cinnamomi and native vegetation. The first was based on those sites that had annual mean temperature more than 7.5°C and annual mean rainfall less than 600 mm. The second included those sites that matched the values of the Pc+ ive set for all seven good discriminators. The two approaches produced similar results. Areas in which even the most favourable microsites are unlikely to support pathogenic activity by P. cinnamomi constitute less than 20% of the land area. Twelve substantial areas of native vegetation that occur in climates suited to infection by P. cinnamomi. but for which no record of the fungus exists, have been identified.     

Growth of three legume trees inoculated with VA mycorrhizal fungi and Rhizobium

Effectiveness among four VA mycorrhizal fungi and Rhizobium (R) in promoting growth of three legume trees in a P-deficient soil was studied.Glomus fasciculatus + R andGigaspora margarita + R were most effective forAcacia mangium andAlbizia falcataria (syn.:Paraserianthes falcataria). Scutellospora persica + R,Gigaspora margarita + R andGlomus fasciculatus + R were most effective forAcacia auriculifornis. Consistently poor growth was attained by seedlings inoculated withSclerocystis clavispora + R,Rhizobium alone, or by uninoculated seedlings.     

Selection of efficient VA mycorrhizal fungi

Summary A procedure is described for selection and screening of VA mycorrhizal fungi in pot and field trials. The VA mycorrhizal fungi from 20 farm paddocks with unexpectedly high pasture production were compared withGlomus fasciculatus for ability to stimulate plant growth. The fungi from three soils (F4, F11, and F20) which were 84–142% more effective thanG. fasciculatus at stimulating growth in sterilised soils were then tested for ability to stimulate clover growth in unsterilised soils in pots, and in the field. F4, F11 and F20 were more efficient thanG. fasciculatus and the indigenous mycorrhizal fungi in all except one field soil.     

Delimitation and classification ofBromus fasciculatus (Poaceae)

The syntypes ofBromus madritensis var.delilei Boiss. comprise two different elements: specimens ofB. haussknechtii Boiss. and ofB. fasciculatus C. Presl s.l. By its lectotypification and on the basis of new morphological characters, the validation ofB. fasciculatus subsp.delilei (Boiss.)H. Scholz 1971 was substantiated. This subspecies represents the eastern marginal segregate of the south-Mediterranean species.B. fasciculatus var.alexandrinus Thell. is a minor variant of the typical subspecies.Dedicated to Prof.K. H. Rechinger on the occasion of his 80th birthday.     

Taxonomic value of a betaine lipid in Ectocarpus (Phaeophyceae) and the first record of a sexual population of E. fasciculatus for the Pacific Ocean

The betaine lipid DGTA differentiates between two species of Ectocarpus: it is present in E. fasciculatus Harvey, and lacking in E. siliculosus (Dillwyn) Lyngbye, Two ectocarpoid isolates from the coast of Chile, which could not be identified to species level, were found to belong to opposite DGTA types. Culture experiments showed that these plants were sporophytes. Their meiospores produced gametophytes of the species predicted by the lipid analysis. Promoted by this new approach, a sexual population of Ectocarpus fasciculatus has been detected for the first time in the Pacific Ocean.     

The Microscopic Examination of Phytophthora cinnamomi in Plant Tissues Using Fluorescent In Situ Hybridization

The microscopic examination of Phytophthora cinnamomi in plant tissues is often difficult as structures such as hyphae, chlamydospores and oospores are frequently indistinguishable from those of other fungi and oomycetes, with histological stains not enabling species differentiation. This lack of staining specificity makes the localization of P. cinnamomi hyphae and reproductive structures within plant tissues difficult, especially in woody tissues. This study demonstrates that with the use of a species‐specific fluorescently labelled DNA probe, P. cinnamomi can be specifically detected and visualized directly using fluorescent in situ hybridization (FISH) without damage to plant or pathogen cell integrity or the need for subculturing. This approach provides a new application for FISH with potential use in the detailed study of plant–pathogen interactions in plants.     

Worldwide occurrence of virus-infections in filamentous marine brown algae

Virus infections were detected inEctocarpus siliculosus andEctocarpus fasciculatus on the coasts of Ireland, California, Peru, southern South America, Australia and New Zealand; in threeFeldmannia species on the coasts of Ireland, continental Chile and Archipelago Juan Fernandez (Chile); and inLeptonematella from Antarctica. Natural populations on the Irish coast contained 3% infected plants inE. fasciculatus, and less than 1% inFeldmannia simplex. On the Californian coast, 15 to 25% ofEctocarpus isolates were infected. Virus symptoms were absent inE. siliculosus from Peru, but appeared after meiosis in laboratory cultures. The virus particles inE. fasciculatus are identical in size and capsid structure to those reported forE. siliculosus, while the virus inF. simplex is smaller and has a different envelope. Our findings suggest that virus infections are a common and worldwide phenomenon in filamentous brown algae.     

Current and projected global distribution of Phytophthora cinnamomi,one of the world's worst plant pathogens

Globally, Phytophthora cinnamomi is listed as one of the 100 worst invasive alien species and active management is required to reduce impact and prevent spread in both horticulture and natural ecosystems. Conversely, there are regions thought to be suitable for the pathogen where no disease is observed. We developed a climex model for the global distribution of P. cinnamomi based on the pathogen's response to temperature and moisture and by incorporating extensive empirical evidence on the presence and absence of the pathogen. The climex model captured areas of climatic suitability where P. cinnamomi occurs that is congruent with all available records. The model was validated by the collection of soil samples from asymptomatic vegetation in areas projected to be suitable by the model for which there were few records. DNA was extracted, and the presence or absence of P. cinnamomi was determined by high‐throughput sequencing (HTS). While not detected using traditional isolation methods, HTS detected P. cinnamomi at higher elevations in eastern Australia and central Tasmania as projected by the climex model. Further support for the climex model was obtained using the large data set from south‐west Australia where the proportion of positive records in an area is related to the Ecoclimatic Index value for the same area. We provide for the first time a comprehensive global map of the current P. cinnamomi distribution, an improved climex model of the distribution, and a projection to 2080 of the distribution with predicted climate change. This information provides the basis for more detailed regional‐scale modelling and supports risk assessment for governments to plan management of this important soil‐borne plant pathogen.     

Immunological Discrimination of Phytophthora cinnamomi from other Phytophthorae Pathogenic on Chestnut

A polyclonal antiserum (A379) against water soluble proteins from Phytophthora cinnamomi mycelium was produced in rabbit. In ELISA, the 1 : 10 000 diluted antiserum revealed only Phytophthora isolates, not allowing a clear‐cut discrimination among congenerous species, in spite of a generally higher reactivity on P. cinnamomi proteins. The antiserum gave positive reactions in Western blot analyses against mycelial proteins from nine species of Phytophthora and Pythium sp. (grown on rich media), but not with Rhizoctonia solani, binucleate Rhizoctonia, Verticillium dahliae, Fusarium oxysporum and Cryphonectria parasitica. All Phytophthora species showed common epitopes on proteins of molecular masses 77, 66, 51 and 48 kDa. However, a species‐specific protein of 55 kDa was immunodecorated only in P. cinnamomi samples, thus allowing univocal identification of this species. When tested against total proteins from the same fungi grown on water, the antibody revealed diagnostic bands of 55 and 51 kDa in P. cinnamomi only. The antiserum is therefore suitable for the specific identification of P. cinnamomi emerging in distilled water from infected tissues of chestnut, blueberry and azalea.     

Induction of resistance in Camellia sinensis against Sclerotium rolfsii by dual application of Rhizophagus fasciculatus and Bacillus pumilus

Rhizophagus fasciculatus and Bacillus pumilus, isolated from rhizosphere of tea (Camellia sinensis (L.) O.Kuntze) bushes, were selected for the present study. Inoculation of tea bushes with any of the two micro-organisms increased growth of plants but significant increase was obtained in case of dual application. B. pumilus exhibited plant growth promoting rhizobacterial traits and antagonistic activity against Sclerotium rolfsii in vitro. Disease reduction following application of R. fasciculatus and B. pumilus was obtained when applied individually but joint application gave more significant results. A sharp increase was found in polyphenolic accumulation and activities of four defence enzymes which play a key role in disease suppression. Immunodetection of S. rolfsii in soil was done after treatments with bioinoculants using PAb of S. rolfsii and its population was significantly reduced owing to application of B. pumilus and R. fasciculatus.     

THE ROLE OF ENDOMYCORRHIZAE IN REVEGETATION PRACTICES IN THE SEMI-ARID WEST. II. A BIOASSAY TO DETERMINE THE EFFECT OF LAND DISTURBANCE ON ENDOMYCORRHIZAL POPULATIONS

Populations of the endomycorrhizal fungus Glomus fasciculatus were significantly reduced following land disturbance in western Colorado soil. A bioassay was developed to measure changes in the endomycorrhizal population. In the bioassay, inoculum levels were measured by comparing the percentage infection in corn (Zea mays) root systems thirty days after planting in undisturbed or disturbed soils. The percentage infection was 2% in the disturbed soil compared to 77% in the adjacent undisturbed soil. Glomus fasciculatus was identified as the endophyte in both soils. Considering the importance and function of endomycorrhizal fungi to their plant hosts the reduction of active inoculum in the disturbed soil may be an important ecological factor in subsequent succession.     

Distribution of Phytophthora cinnamomi at different spatial scales: When can a negative result be considered positively?

Abstract In October 1999, patches of dead and dying trees were identified in rainforest vegetation throughout the Tully Falls area in north Queensland, Australia. Previous incidents of patch death in the region had been attributed to Phytophthora cinnamomi. The distribution of P. cinnamomi was assessed by testing for its presence in seven sites displaying signs of dieback and seven sites that appeared healthy. Each site was a circular quadrat, 20‐m radius (total area = 1256.6 m²). Within each quadrat, two perpendicular line transects were constructed. A single soil sample (250 g) was taken at the centre point and at 1‐m intervals along each transect. All soil samples were tested for the presence of P. cinnamomi using a combination of lupin baiting, subsequent culturing and microscopic identification. Of the 1134 samples, 783 recorded positive responses. The mean number of positive responses was not significantly greater in patch death sites than in control sites, suggesting that at this scale of resolution the distribution of P. cinnamomi was uniform. However, at spatial scales of 1‐m intervals across transects the distribution of P. cinnamomi was random.     

Benzoic acid induces tolerance to biotic stress caused by Phytophthora cinnamomi in Banksia attenuata

Banksia attenuata plants were treated with soil drenches or foliar sprays of benzoic acid (BZA) to determine induced resistance to Phytophthora cinnamomi. Stems of B. attenuata were inoculated with the pathogen 1 week after treatment with BZA. Resistance was estimated by measuring P. cinnamomi lesions on stems. Treatment with 0.10 mM, 0.25 mM or 0.50 mM BZA caused a reduction in lesion size with 0.50 mM BZA applied as a soil drench being the most effective treatment at suppressing the development of lesions. This is the first report of BZA induced host resistance in any plant species to any pathogen.     

Inter-specific differences in responses to copper by natural populations of Ectocarpus

Two species of Ectocarpus, E. siliculosus (Dillw.) Lyngb. and E. fasciculatus Harv., occupying the same habitat at Port St Mary, Isle of Man, and apparently subject to the same environmental conditions, exhibit markedly different responses to copper.

The greater tolerance shown by E. siliculosus is unlikely to be attributable to direct local selection, but may result from immigration of copper-tolerant individuals from highly selective habitats nearby. E. siliculosus would appear to be a more variable species than E. fasciculatus, thereby being more readily affected by the forces of natural selection.     

Phosphite stimulated histological responses of Eucalyptus marginata to infection by Phytophthora cinnamomi

Phosphite is used to protect plants from the soil borne pathogen, Phytophthora cinnamomi. Although phosphite stimulates resistance to P. cinnamomi, this is the first histological study of its effect on Eucalyptus marginata, an economically important forest tree in Western Australia. Clonal lines of E. marginata, considered resistant and susceptible to P. cinnamomi, were underbark inoculated with P. cinnamomi. 4 days later, they were treated with 0, 2.5, 5 or 10 g L⁻¹ phosphite. Transverse hand sections were stained for suberin and lignin, and histological responses to infection were examined. Defence responses were stimulated at all phosphite concentrations in both clonal lines, and the genotypic difference in lesion length was eliminated within 8 days of treatment. In the resistant line, suberin production was stimulated while in the susceptible line both lignin and suberin were stimulated. By 2 days after treatment, phosphite stimulated a faster rate of suberin production in the resistant line than the susceptible line, but by 4 days after treatment, there was no difference in the increase between the lines. Damage caused by P. cinnamomi was found to extend furthest in the cortex and outer phloem in transverse sections in both genotypes. In the presence of P. cinnamomi, phosphite stimulated mitosis as part of the defence response, with meristematic activity involved in the compartmentalisation of damaged tissue (formation of periderm) and closure of healthy tissue (callus). Phytotoxicity had a detrimental effect in healthy tissues and this was more apparent in the resistant line, where it did not provide the best protection from lesion extension and plant mortality, suggesting phytotoxicity could disrupt defence responses. Phosphite increases the capacity of susceptible and resistant E. marginata clonal lines to wall-off and contain P. cinnamomi colonisation through lignin and suberin deposition, and increased meristematic activity.