Take-all disease: New insights into an important wheat root pathogen

Take-all disease, caused by the fungal root pathogen Gaeumannomyces tritici, is considered to be the most important root disease of wheat worldwide. Here we review the advances in take-all research over the last 15 years, focusing on the identification of new sources of genetic resistance in wheat relatives and the role of the microbiome in disease development. We also highlight recent breakthroughs in the molecular interactions between G. tritici and wheat, including genome and transcriptome analyses. These new findings will aid the development of novel control strategies against take-all disease. In light of this growing understanding, the G. tritici-wheat interaction could provide a model study system for root-infecting fungal pathogens of cereals

Impact of 2,4-diacetylphloroglucinol on Gaeumannomyces graminis var. tritici and wheat in the take-all pathosystem

Take-all, caused by Gaeumannomyces graminis var. tritici (Ggt), develops where wheat is grown under moist conditions. It is the most important root disease of wheat worldwide. Take-all decline (TAD) is the spontaneous decrease in take-all incidence and severity induced by continuous wheat or barley monoculture after a severe outbreak of the disease. The build-up of 2,4-diacetylphloroglucinol (2,4-DAPG)-producing Pseudomonas fluorescens (phlD+) during monoculture is responsible for TAD. More than 177 Ggt isolates were isolated from fields with different cropping histories. Sensitivity of Ggt to 2,4-DAPG was not correlated with cropping history, indicating that wheat monoculture does not lead to the emergence of 2,4-DAPG insensitive isolates of the pathogen. Gaeumannomyces-Phialophora complex were isolated from three reduced-till TAD fields in Eastern Washington and identified as Phialophora sp. Phialophora sp. showed less sensitivity to 2,4-DAPG than did isolates of Ggt. The Phialophora isolates may be contributing some level of take-all suppression in the field. A genome-wide deletion library of Saccharomyces cerevisiae was screened for sensitivity to 2,4-DAPG. The screen identified 231 mutants with increased sensitivity to 2,4-DAPG. The targeted mutants were impaired in three cellular physiological functions: membrane function, reactive oxygen regulation, and cellular homeostasis. 2,4-DAPG showed a chemical-genetic fitness data profile similar to the profiles of menthol, sodium azide, and hydrogen peroxide. These findings suggest that 2,4-DAPG inhibits S. cerevisiae, and presumably other fungi, through multiple targets at basic cellular processes. Accumulation of 2,4-DAPG was greatest at two weeks after planting and decreased over the next four weeks. The half life of 2,4-DAPG introduced artificially onto wheat roots with adhering rhizosphere soil was 6 hours. When wheat seedlings were grown on plates amended with 2,4-DAPG (10 [mu]g ml-1) roots showed stunting and brownish necrosis. Levels of 2,4-DAPG sufficient to cause phytotoxicity may in some cases accumulate on roots.A combination of P. fluorescens Q8r1-96 and host plant that supports moderate amounts of 2,4-DAPG accumulation showed the best suppression of take-all. Combinations that resulted in the greatest amount of 2,4-DAPG accumulation, failed to control the disease. This result indicated that a suitable amount of 2,4-DAPG is needed to maximize the biocontrol effect

\u3cem\u3eBrassica\u3c/em\u3e Mulches and Meal Control Fungal Wheat Pathogens \u3cem\u3ein vitro\u3c/em\u3e and Take-all Disease in Soil

Soilborne pathogens have an economic impact on crops throughout the world. Many survive saprophytically and therefore are difficult to control. Soil fumigation and seed treatments are sometimes effective. However, they are economically impractical for many crops. Crop rotation/alternative crops are often a practical, economical, and successful means of controlling soilborne pathogens. Recent studies have revealed that Brassica spp. Inhibit a wide array of plant pathogens. Decomposing species of Brassica release glucosinolates, which are converted to isothiocyanates (ITC) by the enzyme myrosinase. The ITC compounds inhibit microorganisms. The present study had three objectives. The first was to evaluate the effect of Brassica spp. On growth of Gaeumannomyces graminis var. tritici (Ggt), Fusarium oxysporum, F. solani, and F. graminearum, and to determine if inhibition was fungicidal. The first in vitro bioassay was designed as a 3 x 3 factorial in a completely randomized design (CRD) with three isolates of Ggt and three mulch treatments, with 3 replicates. The second bioassay was a 6 x 6 factorial with six fungi [three isolates of Ggt (A2, WX, and 211.1), F. solani, F. oxysporum, and F. graminearum] and six mulch treatments (B. juncea ‘Florida Broadleaf’ mustard mulch, B. juncea mustard seed meal, B. napus ‘Dwarf Essex Rape’, B. napus canola, wheat, and no mulch) in a CRD with three replicates. Plant tissue was placed in 490-cm3 glass jars covered by inverted Petri dishes containing potato dextrose agar (PDA) with a 1-day-old fungal plug. Colony diameters were recorded for eight days. All fungal pathogens tested were inhibited by B. napus and wheat mulch, but fungal growth resumed when the mulches were removed. No growth was recorded for fungi exposed to B. juncea mulch and seed meal, where inhibition was fungicidal. The second objective of the present study was to determine the amount of allyl isothiocyanate (AITC) needed to inhibit growth of the take-all pathogen. The tests were designed in a CRD with five rates of AITC or five rates of B. juncea seed meal. Gaeumannomyces graminis var. tritici isolate WX was exposed to AITC, a dominant isothiocyanate compound found in Brassica spp. Treatments of pure AITC and AITC from B. juncea mustard seed meal (mixed with water) at 0, 0.01, 0.02, 0.03, and 0.04 g were evaluated for the effects on Ggt growth. Petri plates with PDA and 1-day-old fungal plugs were inverted over 490- cm3 glass jars with AITC or seed meal treatments for 5 h. Headspace concentrations of pure AITC and AITC volatized from B. juncea seed meal were recorded after 1 and 2 h; mycelial diameter was measured for 9 days to determine suppression or death of the fungus. Mycelial growth was inhibited by all B. juncea seed meal treatments. The concentrations of AITC produced by B. juncea seed meal that inhibited 50 and 90% of mycelial growth were 0.43 and 0.80 μmol∙liter-1, respectively. Inhibition attributable to pure AITC alone was higher than that achieved by B. juncea seed meal. The third objective of the present study was to determine if incorporating B. juncea mustard mulch into soil containing Ggt-infested wheat crowns would reduce take-all in a subsequent wheat crop, and to evaluate phytotoxicity of Brassica mulch to wheat seedlings. The experiment was designed as a factorial in a split plot with two rates of Ggt (present or absent), two rates of B. juncea ‘Florida Broadleaf’ mulch (present or absent), and ten replicates. The main plot was Brassica mulch; the sbu-plot was Ggt. There were ten plants per replicate and the study was repeated. For the initial crop, wheat seeds were planted into soil in plastic containers with and without inoculum of Ggt, isolates A2 and WX, and maintained in a growth chamber 18˚C. After 28 days, shoots were excised and wheat roots were left in soil. Soils with healthy and diseased roots were mulched with ‘Florida Broadleaf’ mustard for five days; mulch was not applied to controls. For the ‘final crop’ wheat seeds were replanted into soil; take-all severity, shoot height, and percent germination were measured after 28 days. The main effects of mulch and Ggt, and the interaction were significant for disease severity in two trials. Treatment of soil containing Ggt-infected roots with Brassica mulch significantly reduced take-all in the subsequent wheat planting in two tests. In one test, height of seedlings was reduced in soil with Brassica mulch and seedling germination was reduced with Brassica mulch regardless of the presence of Ggt

The biocontrol bacterium Pseudomonas fluorescens Pf29Arp strain affects the pathogenesis-related gene expression of the take-all fungus Gaeumannomyces graminis var. tritici on wheat roots

The main effects of antagonistic rhizobacteria on plant pathogenic fungi are antibiosis, fungistasis or an indirect constraint through the induction of a plant defence response. To explore different biocontrol mechanisms, an in vitro confrontation assay was conducted with the rhizobacterium Pseudomonas fluorescens Pf29Arp as a biocontrol agent of the fungus Gaeumannomyces graminis var. tritici (Ggt) on wheat roots. In parallel with the assessment of disease extension, together with the bacterial and fungal root colonization rates, the transcript levels of candidate fungal pathogenicity and plant-induced genes were monitored during the 10-day infection process. The bacterial inoculation of wheat roots with the Pf29Arp strain reduced the development of Ggt-induced disease expressed as attack frequency and necrosis length. The growth rates of Ggt and Pf29Arp, monitored through quantitative polymerase chain reaction of DNA amounts with a part of the Ggt 18S rDNA gene and a specific Pf29Arp strain detection probe, respectively, increased throughout the interactions. Bacterial antagonism and colonization had no significant effect on root colonization by Ggt. The expression of fungal and plant genes was quantified in planta by quantitative reverse transcription-polymerase chain reaction during the interactions thanks to the design of specific primers and an innovative universal reference system. During the early stages of the tripartite interaction, several of the fungal genes assayed were down-regulated by Pf29Arp, including two laccases, a β-1,3-exoglucanase and a mitogen-activated protein kinase. The plant host glutathione-S-transferase gene was induced by Ggt alone and up-regulated by Pf29Arp bacteria in interaction with the pathogen. We conclude that Pf29Arp antagonism acts through the alteration of fungal pathogenesis and probably through the activation of host defences

In vitro screening of the effect of three glucosinolate derived nitriles on soil-borne fungi

Glucosinolates are allelochemicals present in all plants of the order Capparales that are hydrolysed by endogenous enzymes (myrosinases) forming a variety of compounds with biological activity. ‘Biofumigation’ is the term used to describe the effect of these compounds on soil-borne pathogens and it has normally been attributed to isothiocyanates. At acidic pH and in the presence of redox co-factors such as glutathione, glucosinolate hydrolysis yields also nitriles, which are more hydrophilic and stable than isothiocyanates. Three nitriles (allyl-, benzyl- and phenethyl cyanide) were tested against soil borne fungi of economic importance: Aphanomyces euteiches var. pisi, Gaeumannomyces graminis var. tritici and Verticillium dahliae. The nitriles were initially tested at 1 mM and four additional concentrations were further tested in order to determine LD50. At 1 mM, allyl cyanide showed in all cases less than 10% inhibition and it did not inhibit fungi growth at higher concentrations. LD50 of benzyl cyanide was 2.5 mM for Verticillium and Aphanomyces, whereas it was as low as 0.5 mM for Gaeumannomyces. LD50 of phenyl ethyl cyanide was 2.5 mM for Verticillium, 1.4 mM Gaeumannomyces and 1.25 mM Aphanomyces. Although nitriles are generally less toxic than ITCs, their role in biofumigation should not be disregarded

Production of mutants of Gaeumannomyces graminis var. tritici and var. avenae by 4- nitroquinolene-oxide treatment of protoplasts.

The ascomycete fungus Gaeumannomyces graminis is the causative agent of take-all disease of cereals. Much information about the physiology and pathology of this organism has been generated (Asher and Shipton (Eds.) Biology and Control of Take-All , Academic Press, 1981), but genetic studies such as the production of mutants have been hindered by problems in obtaining viable propagules suitable for mutagenesis (Blanch et al. 1981. Trans. Brit. Mycol. Soc. 77:391-399). The fungus is homothallic but many strains cannot be induced to form perithecia in culture and even the fertile strains produce insufficient numbers of ascospores for use in mutagenesis. It is, however, possible to produce and regenerate large numbers of protoplasts and Rochefrette et al

Evaluation of Ultradwarf Bermudagrass Cultural Management Practices and Identification, Characterization, and Pathogenicity of Ectotrophic Root-Infecting Fungi Associated with Summer Decline of Ultradwarf Bermudagrass Putting Greens

This research addressed the effects of cultural management practices, cultivar selection, and applications of seasonal fungicides on ultradwarf bermudagrass health and playability and occurrence of foliar diseases. Additionally, novel ectotrophic root-infecting fungi were isolated from ultradwarf bermudagrass roots exhibiting symptoms of summer decline, identified via multilocus phylogenetic analyses, and characterized by morphological assessments and pathogenicity evaluations

Development of a PCR assay to quantify take-all pathogens of wheat

Take-all is a disease in wheat which can cause significant yield losses. If it was possible to predict these losses, by competitive PCR, agronomic decisions could be made to reduce them. As the causal agent, Gaeumannomyces graminis, is found in the soil organic matter, soil DNA extraction methods were tested for their efficacy. An inhibition assay was designed to test the level of inhibition present in DNA extracted from soil. Of the extractions tested the CTAB extraction was the most successful at removing inhibitors and the commercially available Soil DNA Isolation Kit ™ was the least successful. All extraction methods tested required some dilution to enable the amplification of the inhibition standard. Soil DNA extraction was found to be time consuming so stem bases and roots were used with the competitive PCR assay. To create a quantitative competitive PCR assay published primers were amplified with known G. graminis isolates. They produced unexpected results which meant that they were unsuitable for use in a competitive PCR assay. Consequently HAGG primers were designed and successfully amplified known G. graminis var. tritici and var. avenae isolates, and isolated G. graminis from take-all infected wheat plants. The HAGG competitive PCR assay was used to quantify the presence of the take-all pathogen in a large number of plant samples ranging in age. Regressions of DNA concentration and visual symptoms or yield did not result in strong correlations. Analysis suggested the variability between the fields explained a large proportion of variability. A large scale experiment was completed to compare the impact of various seed treatments on pathogen DNA concentration, visual disease assessment, grain quality and yield. Early assessment of the plant material demonstrated the heterogeneous nature of this disease. When taking the pathogen DNA concentration at stubble into account a Latitude® (silthiofam) seed treatment achieved the greatest yield; Baytan® (triadimenol and fuberidazole) resulted in the lowest yield. The experiment demonstrated that this competitive PCR assay has the potential in field experiments to take account of the initial inoculum load

Антагонистическая активность штамма Pseudomonas fluorescens 2303 по отношению к фитопатогенам

Досліджено антагонізм штаму Pseudomonas fluorescens 2303 стосовно фітопатогенних бактерій і грибів. Цей штам пригнічував розвиток P.syringae pv. syringae 8511, P.syringae pv. atrofaciens 9400, Xantomonas campestris 8003б, Clavibacter michiganensis 102 — зони затримки росту становили 20—40 мм. Штам P.fluorescens 2303, на відміну від штамів препарату гаупсин, пригнічував розвиток таких фітопатогенних бактерій, як Pectobacterium carotovorum 8982 та Agrobacterium tumefaciens 8626. Штам P.fluorescens 2303 виявився високоактивним стосовно фітопатогенних грибів і був, у середньому, в два рази активнішим за штам препарату для захисту рослин — гаупсину. Зокрема, індекс пригнічення розвитку збудника офіобольозної кореневої гнилі Gaeumannomyces graminis var. tritici 10Z у 9,4 разу перевищував відповідне значення для гаупсину. За результатами проведених досліджень штам P.fluorescens 2303 є перспективним для застосування у сільському господарстві для комплексного захисту рослин від фітопатогенних грибів та бактерій, а також для розроблення препарату на основі цього штаму.In this paper, we study the antagonism of Pseudomonas fluorescens 2303 strain on pathogenic bacteria’s and fungi’s. This strain inhibited the development of P.syringae pv. syringae 8511, P.syringae pv. atrofaciens 9400, Xantomonas campestris 8003b, Clavibacter michiganensis 102 — stunting zones were 20—40 mm. Strain P.fluorescens 2303, unlike the product haupsyn, inhibited the growth of pathogenic bacteria such as Pectobacterium carotovorum 8982 and 8626 Agrobacterium tumefaciens. P.fluorescens 2303 strain was highly active against phytopathogenic fungi and was on average two times more active than the strain of plant protection product — gaupsin. In particular, the inhibition index of root rots caused by Gaeumannomyces graminis var. tritici 10Z is 9,4 times higher than the corresponding value for gaupsin. The research into P.fluorescens 2303 strain is promising for its applying in agriculture for comprehensive plants protection of plants against pathogenic fungi and bacteria, as well as for developing a product based on this strain.Исследован антагонизм штамма Pseudomonas fluorescens 2303 по отношению к фитопатогенным бактериям и грибам. Данный штамм подавлял развитие P.syringae pv. syringae 8511, P.syringae pv. atrofaciens 9400, Xantomonas campestris 8003б, Clavibacter michiganensis 102 — зоны задержки роста составляли 20—40 мм. Штамм P.fluorescens 2303, в отличие от штаммов препарата гаупсин, подавлял развитие таких фитопатогенных бактерий, как Pectobacterium carotovorum 8982 и Agrobacterium tumefaciens 8626. Штамм P.fluorescens 2303 оказался высокоактивным по отношению к фитопатогенным грибам и был, в среднем, в два раза более активный чем штамм препарата для защиты растений — гаупсина. В частности, индекс угнетения развития возбудителя офиоболезной корневой гнили Gaeumannomyces graminis var. tritici 10Z в 9,4 раза превышал соответствующее значение для гаупсина. По результатам проведенных исследований штамм P.fluorescens 2303 является перспективным для использования в сельском хозяйстве для комплексной защиты растений от фитопатогенных грибов и бактерий, а также для разработки препарата на основе данного штамма

Evaluation of Ultradwarf Bermudagrass Cultural Management Practices and Identification, Characterization, and Pathogenicity of Ectotrophic Root-Infecting Fungi Associated with Summer Decline of Ultradwarf Bermudagrass Putting Greens

This research addressed the effects of cultural management practices, cultivar selection, and applications of seasonal fungicides on ultradwarf bermudagrass health and playability and occurrence of foliar diseases. Additionally, novel ectotrophic root-infecting fungi were isolated from ultradwarf bermudagrass roots exhibiting symptoms of summer decline, identified via multilocus phylogenetic analyses, and characterized by morphological assessments and pathogenicity evaluations