Root diseases have long been prevalent in Australian grain-growing regions, and most management decisions to reduce the risk of yield loss need to be implemented before the crop is sown. The levels ...of pathogens that cause the major root diseases can be measured using DNA-based services such as PreDicta B. Although these pathogens are often studied individually, in the field they often occur as mixed populations and their combined effect on crop production is likely to vary across diverse cropping environments. A 3-year survey was conducted covering most cropping regions in Western Australia, utilizing PreDicta B to determine soilborne pathogen levels and visual assessments to score root health and incidence of individual crop root diseases caused by the major root pathogens, including Rhizoctonia solani (anastomosis group AG-8), Gaeumannomyces graminis var. tritici (take-all), Fusarium pseudograminearum, and Pratylenchus spp. (root-lesion nematodes) on wheat roots for 115, 50, and 94 fields during 2010, 2011, and 2012, respectively. A predictive model was developed for root health utilizing autumn and summer rainfall and soil temperature parameters. The model showed that pathogen DNA explained 16, 5, and 2% of the variation in root health whereas environmental parameters explained 22, 11, and 1% of the variation in 2010, 2011, and 2012, respectively. Results showed that R. solani AG-8 soil pathogen DNA, environmental soil temperature, and rainfall parameters explained most of the variation in the root health. This research shows that interactions between environment and pathogen levels before seeding can be utilized in predictive models to improve assessment of risk from root diseases to assist growers to plan more profitable cropping programs.
Novel species of microfungi described in the present study include the following from Australia: Phytophthora amnicola from still water, Gnomoniopsis smithogilvyi from Castanea sp., Pseudoplagiostoma ...corymbiae from Corymbia sp., Diaporthe eucalyptorum
from Eucalyptus sp., Sporisorium andrewmitchellii from Enneapogon aff. lindleyanus, Myrmecridium banksiae from Banksia, and Pilidiella wangiensis from Eucalyptus sp. Several species are also described from South Africa, namely: Gondwanamyces
wingfieldii from Protea caffra, Montagnula aloes from Aloe sp., Diaporthe canthii from Canthium inerne, Phyllosticta ericarum from Erica gracilis, Coleophoma proteae from Protea caffra, Toxicocladosporium strelitziae from Strelitzia reginae,
and Devriesia agapanthi from Agapanthus africanus. Other species include Phytophthora asparagi from Asparagus officinalis (USA), and Diaporthe passiflorae from Passiflora edulis (South America). Furthermore, novel genera of coelomycetes include Chrysocrypta
corymbiae from Corymbia sp. (Australia), Trinosporium guianense, isolated as a contaminant (French Guiana), and Xenosonderhenia syzygii, from Syzygium cordatum (South Africa). Pseudopenidiella piceae from Picea abies (Czech Republic),
and Phaeocercospora colophospermi from Colophospermum mopane (South Africa) represent novel genera of hyphomycetes. Morphological and culture characteristics along with ITS DNA barcodes are provided for all taxa.
During one spring season, 12
Phytophthora
species, two
Phytophthora
hybrids, three
Halophytophthora
species and three
Phytopythium
species, were isolated from 48 waterways across Western Australia. ...The waterways were sampled using nylon mesh bags containing leaf baits of up to six different plant species and were isolated by plating necrotic lesions on these onto
Phytophthora
-selective agar media.
Phytophthora
species were isolated from all except one waterway. Of the
Phytophthora
species isolated, eight are known while the remaining four are undescribed taxa. Six of the
Phytophthora
species and the two hybrids are from clade 6. The two hybrids and
P. inundata
were the predominant species recovered. Recoveries from different plant leaf baits varied with the best two baits being
Pittosporum undulatum
and
Banksia attentuata
; and from these two combined all
Phytophthora
species were isolated. There was a marked difference in the
Phytophthora
diversity in the waterways from different regions. This is the first comprehensive study from Australia to examine the
Phytophthora
communities in waterways, and advances our understanding of the role of these oomycetes in natural and anthropized ecosystems.
Water used for the irrigation of plants has the potential to harbour and spread plant pathogens yet little research is conducted within this field. This review was undertaken to critically review ...current understanding of waterborne fungal and oomycete plant pathogens in open irrigation systems, particularly in the context of plant biosecurity. It was determined that very limited data exists on these plant pathogens, with the majority of previous studies only recording pathogen presence. There are significant gaps in current knowledge of pathogen survival and spread, and very limited information on their ability to cause disease when contaminated irrigation water is applied to crops. This review highlights the need for new research on the epidemiology and pathogenicity of putative plant pathogens isolated from water, in order to determine their risk to crops. The importance of regular monitoring of irrigation systems for the early detection of plant pathogens is also discussed.
Umbellularia californica is one of the key infectious hosts of the exotic Phytophthora ramorum, which causes sudden oak death (SOD) in California and Oregon forests. This study provides a ...comprehensive analysis of the epidemiologically relevant parameters for SOD in California and southern Oregon, including potential differences between the two states. Experimental infection of U. californica leaves was optimal when leaves were wet for 6–12 h, temperature was approximately 19°C and pathogen concentration was approximately 2·7 × 104 zoospores mL−1. Seasonal variation in host susceptibility and disease incidence was examined for two populations by inoculating detached leaves at 12 dates and by monitoring naturally infected leaves, respectively. Susceptibility of U. californica and disease incidence varied significantly in time and the variation was highest for both in spring. Susceptibility of trees from 17 natural populations from California and southern Oregon was assessed in detached leaf inoculations. One California and three southern Oregon populations had significantly and repeatable lower average susceptibility in artificial inoculations, but differences among three selected California and Oregon populations were not significant in inoculations of seedlings grown from seed in a common garden. This study concludes that U. californica susceptibility has a large environmental component, yet still predicts potential disease severity in different sites especially where infestations are young or the pathogen has not yet arrived. The accuracy and utility of predictive risk models for P. ramorum will be enhanced by the inclusion of both the environmental and host susceptibility components.
Novel species of microfungi described in the present study include the following from Australia: Bagadiella victoriae and Bagadiella koalae on Eucalyptus spp., Catenulostroma eucalyptorum on ...Eucalyptus laevopinea, Cercospora eremochloae on Eremochloa
bimaculata, Devriesia queenslandica on Scaevola taccada, Diaporthe musigena on Musa sp., Diaporthe acaciigena on Acacia retinodes, Leptoxyphium kurandae on Eucalyptus sp., Neofusicoccum grevilleae on Grevillea aurea, Phytophthora
fluvialis from water in native bushland, Pseudocercospora cyathicola on Cyathea australis, and Teratosphaeria mareebensis on Eucalyptus sp. Other species include Passalora leptophlebiae on Eucalyptus leptophlebia (Brazil), Exophiala tremulae
on Populus tremuloides and Dictyosporium stellatum from submerged wood (Canada), Mycosphaerella valgourgensis on Yucca sp. (France), Sclerostagonospora cycadis on Cycas revoluta (Japan), Rachicladosporium pini on Pinus monophylla (Netherlands),
Mycosphaerella wachendorfiae on Wachendorfia thyrsifolia and Diaporthe rhusicola on Rhus pendulina (South Africa). Novel genera of hyphomycetes include Noosia banksiae on Banksia aemula (Australia), Utrechtiana cibiessia on Phragmites australis
(Netherlands), and Funbolia dimorpha on blackened stem bark of an unidentified tree (USA). Morphological and culture characteristics along with ITS DNA barcodes are provided for all taxa.
Susceptibility to branch dieback caused by Phytophthora ramorum was tested using a detached branch assay for 66 Australian native plant species sourced from established gardens and arboreta in ...California. Six of these species were further tested for their susceptibility to bole cankers caused by P. ramorum using a sealed log assay. Isopogon formosus and Eucalyptus denticulata were identified as potentially highly susceptible Australian branch dieback hosts. Thirteen potentially tolerant Australian host species included Banksia attenuata, B. marginata, E. haemastoma, E. regnans, Pittosporum undulatum and Billardiera heterophylla. Eucalyptus regnans was identified as a potentially highly susceptible bole canker host, while E. diversicolor and E. viminalis were considered potentially tolerant species to bole cankers caused by P. ramorum. Phytophthora ramorum was able to infect all 66 species, as confirmed by reisolation. These results extend the known potential host range for P. ramorum, confirm it as a possible threat to Australian plant industries and ecosystems and highlight additional associated hosts that are important in the global horticultural trade, native forests and plantation forestry.
Coast live oak (
Quercus agrifolia
) is a known host for
Phytophthora ramorum
, the casual agent of sudden oak death in California, with symptoms expressed as necrotic stem cankers. In the forest, ...leaves on two saplings in California were found to be infected with
P. ramorum
and these were associated with infected bay laurel (
Umbellularia californica
) trees. Coast live oak leaves supported sporulation and produced chlamydospores
in vitro
. This is the first report to identify foliage of coast live oak as a source of infection of
P. ramorum
in the forest and its confirmation in
in vitro
inoculations.
In a series of growth cabinet, glasshouse and field experiments, tissue samples from living clonal Eucalyptus marginata (jarrah) were incubated immediately after sampling on agar (NARPH) selective ...for Phytophthora. Phytophthora cinnamomi was recovered 3-6 months after inoculation from 50% of samples with lesions and 30% of symptomless samples. However, up to 11% of samples with and without lesions and from which P. cinnamomi was not initially isolated contained viable pathogen. This was shown by removing tissue which had not produced any growth of P. cinnamomi on NARPH plates, cutting it into smaller sections, washing in sterile deionised water repeatedly for 9 days, and replating. Plating stem or bark tissue directly onto NARPH produced false-negative results for nine P. cinnarnomi isolates and six jarrah clones. The behaviour of the pathogen indicates that it could be present as dormant structures, such as chlamydospores, that need to be induced to germinate. Alternatively, fungistatic compounds in the tissue needed to be removed to allow the pathogen to grow. These results have important implications for disease diagnosis and management, disease-free certification and quarantine clearance.PUBLICATION ABSTRACT
•Fusarium spp. and Rhizoctonia solani were favoured by cereal dominated rotations.•Pythium spp. and Pratylenchus neglectus were favoured by more diverse rotations.•Windrow burning had little effect ...on amount of stubble-borne disease.•Farmers require up-to-date information on the crop host status.
No-tillage is a cropping system that promotes minimal soil disturbance, full residue retention and diverse crop rotation. From a disease perspective, crop rotation is one of the best control measures in no-tillage systems, as many diseases are stubble-borne. A long-term no-tillage systems experiment was conducted from 2007 to 2016 in Western Australia to test effects of crop rotation and residue amount on soil health, crop growth and yield. The current research focusses on the progression of the main stubble-borne and root diseases and plant-parasitic nematodes in this experiment. The research compared a diverse crop rotation with a ‘typical’ farmer rotation, a cereal rotation and wheat monoculture. Three-year rotations were used and the crops and cultivars were changed periodically, within the rotations, to ensure they were relevant to farmers.
Levels of root lesion nematode (Pratylenchus neglectus) and Pythium increased most in the pasture and diverse rotations, followed by the wheat monoculture and appeared to decrease slightly in the farmer and cereal rotations. The combination of canola and wheat, along with susceptible chickpea, appeared to favour root lesion nematode. In contrast, fallow and lupin in the farmer rotation appeared most effective at reducing levels. The relatively high numbers of P. neglectus in the pasture was likely due to continuous presence of a number of susceptible weeds and subterranean clover. The crop selections in the diverse rotation of this experiment have generally been a poor choice in terms of P. neglectus, the main nematode threat in Western Australia.
By 2016, there was significantly greater Rhizoctonia solani in the soil following cereals compared with canola, chickpea and fallow. Nonetheless, the break crops appeared to have had a relatively short term effect on amounts of R. solani.
Over the nine years, Fusarium spp. DNA in the soil increased most in the cereal rotation and wheat monoculture; it hardly changed in the farmer rotation and pasture and it declined in the diverse rotation.
There was a decrease in Didymella pinodes/Phoma medicaginis var pinodella DNA (causing pea black spot) in the cereal rotation, farmer rotation and wheat monoculture. In contrast, there was a small increase in pea black spot pathogen DNA in the diverse rotation. This generally reflected the number of pea crops grown, except for the farmer rotation, which had peas grown at the same intensity as the diverse rotation. The difference between these two rotations was likely due to the lower amounts of residue in the farmer rotation, which had fallow and tillage since 2013. As expected, there were higher incidence of the stubble-borne disease in wheat and barley when following the same type of crop. Crop residue management, by windrow burning, had little effect on the level of leaf, root or crown diseases.
The differences in host status between crop types and even varieties means that farmers require up-to-date information on the host status if rotations are going to be effective in reducing a broad range of plant-parasitic nematodes and pathogens in soils with no-tillage.
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