Hyperlocal Variation in Soil Iron and the Rhizosphere Bacterial Community Determines Dollar Spot Development in Amenity Turfgrass

ABSTRACT Dollar spot, caused by the fungal pathogen Clarireedia spp., is an economically important foliar disease of amenity turfgrass in temperate climates worldwide. This disease often occurs in a highly variable manner, even on a local scale with relatively uniform environmental conditions. The objective of this study was to investigate mechanisms behind this local variation, focusing on contributions of the soil and rhizosphere microbiome. Turfgrass, rhizosphere, and bulk soil samples were collected from within a 256-m2 area of healthy turfgrass, transported to a controlled environment chamber, and inoculated with Clarireedia jacksonii. Bacterial communities were profiled by targeting the 16S rRNA gene, and 16 different soil chemical properties were assessed. Despite their initial uniform appearance, the samples differentiated into highly susceptible and moderately susceptible groups following inoculation in the controlled environment chamber. The highly susceptible samples harbored a unique rhizosphere microbiome with suggestively lower relative abundance of putative antibiotic-producing bacterial taxa and higher predicted abundance of genes associated with xenobiotic biodegradation pathways. In addition, stepwise regression revealed that bulk soil iron content was the only significant soil characteristic that positively regressed with decreased dollar spot susceptibility during the peak disease development stage. These findings suggest that localized variation in soil iron induces the plant to select for a particular rhizosphere microbiome that alters the disease outcome. More broadly, further research in this area may indicate how plot-scale variability in soil properties can drive variable plant disease development through alterations in the rhizosphere microbiome. IMPORTANCE Dollar spot is the most economically important disease of amenity turfgrass, and more fungicides are applied targeting dollar spot than any other turfgrass disease. Dollar spot symptoms are small (3 to 5 cm), circular patches that develop in a highly variable manner within plot scale even under seemingly uniform conditions. The mechanism behind this variable development is unknown. This study observed that differences in dollar spot development over a 256-m2 area were associated with differences in bulk soil iron concentration and correlated with a particular rhizosphere microbiome. These findings provide interesting avenues for future research to further characterize the mechanisms behind the highly variable development of dollar spot, which may inform innovative control strategies. Additionally, these results suggest that small changes in soil properties can alter plant activity and hence the plant-associated microbial community, which has important implications for a broad array of agricultural and horticultural plant pathosystems.

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Hyperlocal Variation in Soil Iron and Rhizosphere Microbiome Determines Disease Development in Amenity Turfgrass

10.1101/2020.08.17.255265 ◽

2020 ◽

Author(s):

Ming-Yi Chou ◽

Smita Shrestha ◽

Renee Rioux ◽

Paul Koch

Keyword(s):

Soil Properties ◽

Bulk Soil ◽

Controlled Environment ◽

Rrna Gene ◽

Disease Development ◽

Dollar Spot ◽

Rhizosphere Microbiome ◽

Environment Chamber ◽

Plant Pathosystems ◽

Important Disease

ABSTRACTDollar spot, caused by the fungal pathogen Clarireedia spp., is an economically important disease of amenity turfgrass in temperate climates worldwide. This disease often occurs in a highly variable manner, even on a local scale with relatively uniform environmental conditions. The objective of this study was to investigate mechanisms behind this local variation, focusing on contributions of the soil and rhizosphere microbiome. Turfgrass, rhizosphere, and bulk soil samples were taken from within a 256 m2 area of healthy turfgrass, transported to a controlled environment chamber, and inoculated with C. jacksonii. Bacterial communities were profiled targeting the 16s rRNA gene, and 16 different soil chemical properties were assessed. Despite their initial uniform appearance, the samples differentiated into highly susceptible and moderately susceptible groups following inoculation in the controlled environment chamber. The highly susceptible samples harbored a unique rhizosphere microbiome with lower relative abundance of antibiotic-producing bacterial taxa and higher predicted abundance of genes associated with xenobiotic biodegradation pathways. In addition, stepwise regression revealed that bulk soil iron content was the only significant soil characteristic that positively regressed with decreased dollar spot susceptibility during the peak disease development stage. These findings suggest that localized variation in soil iron induces the plant to select for a particular rhizosphere microbiome that alters the disease outcome. More broadly, further research in this area may indicate how plot-scale variability in soil properties can drive variable plant disease development through alterations in the rhizosphere microbiome.IMPORTANCEDollar spot is the most economically important disease of amenity turfgrass, and more fungicides are applied targeting dollar spot than any other turfgrass disease. Dollar spot symptoms are small (3-5 cm), circular patches that develop in a highly variable manner within plot-scale even under seemingly uniform conditions. The mechanism behind this variable development is unknown. This study observed that differences in dollar spot development over a 256 m2 area were associated with differences in bulk soil iron concentration and correlated with a particular rhizosphere microbiome. These findings provide important clues for understanding the mechanisms behind the highly variable development of dollar spot, which may offer important clues for innovative control strategies. Additionally, these results also suggest that small changes in soil properties can alter plant activity and hence the plant-associated microbial community which has important implications for a broad array of important agricultural and horticultural plant pathosystems.

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026 The Effect of Temperature on the Development of Fusarium Stem Rot in Greenhouse Peppers in South Florida

HortScience ◽

10.21273/hortsci.35.3.392d ◽

2000 ◽

Vol 35 (3) ◽

pp. 392D-392

Author(s):

E.M. Lamb ◽

R.M Sonoda ◽

E.F. Oxman ◽

E.N. Rosskopf

Keyword(s):

Lesion Size ◽

South Florida ◽

Stem Rot ◽

Effect Of Temperature ◽

Lesion Length ◽

Controlled Environment ◽

Disease Development ◽

Greenhouse Production ◽

Disease Symptoms ◽

Environment Chamber

Hydroponic greenhouse production of sweet peppers is a well-established and growing industry in South Florida. Plants are in the greenhouse from about October until June, and the long season makes disease problems particularly costly to producers. A stem rot caused by Fusarium solani (anamorph of Nectria haematococca) and previously unreported in South Florida was found on greenhouse peppers in March 1999. Black lesions occurred at nodes where the plant was pruned or fruit was harvested. Tissues above the lesion appeared normal until the lesion girdled the stem, at which point the tissues above the lesion wilted and died. Greenhouse surveys over a 4-month period suggested that environmental factors played a role in number of infected plants and lesion size. A controlled environment chamber test was conducted to evaluate the effect of temperature and cultivar on disease development and severity. Three greenhouse pepper cultivars; Cubico, Triple 4, and Kelvin, were stem inoculated with F. solani at the 3- to 4-week stage. Noninoculated plants were included as a control. Fifteen plants of each cultivar plus control plants were incubated at ≈35, 32, and 29 °C for 2 weeks. The test was run twice. All inoculated plants developed lesions while no control plants developed disease symptoms. Lesion length and diameter were measured for all plants and wilting associated with disease development was noted. Temperature had a significant effect on disease severity with larger lesions and more frequent wilting occurring at higher temperatures. Cultivar did not affect the development of the disease.

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TOLERANCE OF EARLY-MATURING SOYBEAN CULTIVARS TO METRIBUZIN

Canadian Journal of Plant Science ◽

10.4141/cjps86-016 ◽

1986 ◽

Vol 66 (1) ◽

pp. 125-130 ◽

Cited By ~ 6

Author(s):

G. H. FRIESEN ◽

D. A. WALL

Keyword(s):

Sandy Loam ◽

Controlled Environment ◽

Clay Loam ◽

Clay Loam Soil ◽

Soybean Cultivars ◽

Early Maturing ◽

Glycine Max L ◽

Loam Soil ◽

Environment Chamber ◽

Chamber Studies

McCall, Maple Presto, Maple Amber and OT80-3 soybean (Glycine max (L.) Merr.) cultivars were evaluated under field conditions for their response to metribuzin. Maple Amber was found to be less tolerant than the other cultivars. In controlled environment chamber studies, injury to this cultivar was more severe on a sandy loam soil than on a clay loam soil. Fall applications of metribuzin, alone or tank-mixed with trifluralin, were tolerant to Maple Amber soybeans and such applications may offer a practical alternative to spring treatments for broad spectrum weed control in the less tolerant soybean cultivars grown in Manitoba.Key words: Metribuzin, trifluralin, preplant incorporation, fall treatments, soybean cultivars

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Vegetation alters how soil properties and climate influence microbial activity and functional diversity in rhizosphere and bulk soil along an elevation gradient

Soil Biology and Biochemistry ◽

10.1016/j.soilbio.2021.108485 ◽

2021 ◽

pp. 108485

Author(s):

Daniel Hernández-Cáceres ◽

Alexia Stokes ◽

Guillermo Angeles-Alvarez ◽

Josiane Abadie ◽

Fabien Anthelme ◽

...

Keyword(s):

Soil Properties ◽

Microbial Activity ◽

Functional Diversity ◽

Elevation Gradient ◽

Bulk Soil

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Humidity Effects on Porous Silica Thin Films

MRS Proceedings ◽

10.1557/proc-411-419 ◽

1995 ◽

Vol 411 ◽

Cited By ~ 2

Author(s):

J. R. Kokan ◽

R. A. Gerhardt

Keyword(s):

Thin Films ◽

Ac Conductivity ◽

Sol Gel ◽

Porous Silica ◽

Controlled Environment ◽

Alkali Ions ◽

Humidity Effects ◽

Silica Thin Films ◽

Environment Chamber ◽

Humidity Sensitivity

ABSTRACTImpedance Spectroscopy is being used to study the humidity sensitivity of porous silica thin films. The films are processed via a colloidal sol-gel method which leaves some remnant potassium and sodium. Previous work on bulk porous silica samples processed by the same method showed that the dielectric properties and ac conductivity were very sensitive to changes in humidity. The aim of this work was to determine if the same dependencies could be found in the thin films. The capacitance, dielectric loss, and ac conductivity of the films were measured in a controlled environment chamber from 20–80% RH for frequencies ranging from 10Hz–10MHz. In addition to characterizing films with varying amounts of residual alkali ions obtained through leaching, we have also measured films that were surface doped with controlled amounts of KCl, LiCl, or NaCl. Relative humidity dependencies in the films are not as dramatic as in the bulk samples. The reasons for this behavior are not yet clear, but may be associated with the porosity, thickness, and surface area of the films.

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Predominance of soil vs root effect in rhizosphere microbiota reassembly

FEMS Microbiology Ecology ◽

10.1093/femsec/fiz139 ◽

2019 ◽

Vol 95 (10) ◽

Cited By ~ 3

Author(s):

Mengli Zhao ◽

Jun Yuan ◽

Zongzhuan Shen ◽

Menghui Dong ◽

Hongjun Liu ◽

...

Keyword(s):

Bacterial Communities ◽

Disease Incidence ◽

Bulk Soil ◽

Pathogen Population ◽

Root Effect ◽

Rhizosphere Microbiome ◽

Distinct Disease ◽

Pathogenic Microbes ◽

Disease Suppressive Soil ◽

Rhizosphere Community

ABSTRACT Rhizosphere community assembly is simultaneously affected by both plants and bulk soils and is vital for plant health. However, it is still unclear how and to what extent disease-suppressive rhizosphere microbiota can be constructed from bulk soil, and the underlying agents involved in the process that render the rhizosphere suppressive against pathogenic microbes remain elusive. In this study, the evolutionary processes of the rhizosphere microbiome were explored based on transplanting plants previously growing in distinct disease-incidence soils to one disease-suppressive soil. Our results showed that distinct rhizoplane bacterial communities were assembled on account of the original bulk soil communities with different disease incidences. Furthermore, the bacterial communities in the transplanted rhizosphere were noticeably influenced by the second disease-suppressive microbial pool, rather than that of original formed rhizoplane microbiota and homogenous nontransplanted rhizosphere microbiome, contributing to a significant decrease in the pathogen population. In addition, Spearman's correlations between relative abundances of bacterial taxa and the abundance of Ralstonia solanacearum indicated Anoxybacillus, Flavobacterium, Permianibacter and Pseudomonas were predicted to be associated with disease-suppressive function formation. Altogether, our results showed that bulk soil played an important role in the process of assembling and reassembling the rhizosphere microbiome of plants.

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Relative and quantitative rhizosphere microbiome profiling result in distinct abundance patterns

10.1101/2021.02.19.431941 ◽

2021 ◽

Author(s):

Hamed Azarbad ◽

Julien Tremblay ◽

Luke D. Bainard ◽

Etienne Yergeau

Keyword(s):

Water Stress ◽

Relative Abundance ◽

Its Region ◽

Cost Effective ◽

Amplicon Sequencing ◽

Rrna Gene ◽

Real Time Quantitative Pcr ◽

Rhizosphere Microbiome ◽

History Of ◽

Almost All

AbstractNext-generation sequencing is recognized as one of the most popular and cost-effective way of characterizing microbiome in multiple samples. However, most of the currently available amplicon sequencing approaches are inherently limited, as they are often presented based on the relative abundance of microbial taxa, which may not fully represent actual microbiome profiles. Here, we combined amplicon sequencing (16S rRNA gene for bacteria and ITS region for fungi) with real-time quantitative PCR (qPCR) to characterize the rhizosphere microbiome of wheat. We show that the increase in relative abundance of major microbial phyla does not necessarily result in an increase in abundance. One striking observation when comparing relative and quantitative abundances was a substantial increase in the abundance of almost all phyla associated with the rhizosphere of plants grown in soil with no history of water stress as compared with the rhizosphere of plants growing in soil with a history of water stress, which was in contradiction with the trends observed in the relative abundance data. Our results suggest that the estimated absolute abundance approach gives a different perspective than the relative abundance approach, providing complementary information that helps to better understand the rhizosphere microbiome.

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Soil aggregate-based nucleic acid analyses of the impact of maize roots and their root hairs on the structural diversity of microbial communities

10.5194/egusphere-egu21-7620 ◽

2021 ◽

Author(s):

Christoph Tebbe ◽

Damini Damini ◽

Damien Finn ◽

Nataliya Bilyera ◽

Minh Ganther ◽

...

Keyword(s):

16S Rrna ◽

16S Rrna Gene ◽

Root Hair ◽

Soil Aggregates ◽

Root Hairs ◽

Soil Samples ◽

Plant Roots ◽

Bulk Soil ◽

Rrna Gene ◽

The Impact

The deposition of energy rich carbon sources released by plant roots during their growth fuels microbially driven ecosystem processes in soil, but there is a lack of understanding how microorganisms interact and collaborate. The objective of this research was therefore to characterize microbial networks as they assemble under the influence of plant roots. To identify the specific importance of root hairs, we compared the impact of a maize wild-type to a root-air defective mutant (rth3; (1).The microbial community structure was analyzed by qPCR and 16S rRNA gene amplicon sequencing from soil DNA. In order to increase the probability of detecting truly interacting microbial partners as a basis for network analyses, we first evaluated a new protocol to obtain DNA from as little as 1 mg instead of the usual 250 mg soil samples, thereby approaching the aggregate level (2). While the diversity of bacterial 16S rRNA gene amplicons of 250-mg samples taken from the same soil was not distinct, DNA analyses from individual aggregates clearly differed from each other underlining that soil aggregates represent distinct microbial habitats.Soil column experiments with maize grown in a loam soil (3) revealed distinct communities between rhizosphere and bulk soil. The community composition of individual aggregates showed more differences in bulk soil compared to rhizosphere. Less elaborated networks were seen in bulk soil and a profound effect of root hairs could be unravelled. Null model testing demonstrated that Actinobacteria were equally important for network connectivity independent of the root hair mutation, but for networks of the wildtype, Acidobacteria were essential for synergistic interactions and overall network structure. In contrast, Proteobacteria and Firmicutes connectivity became more important. The observed differences in community composition and interactions suggests carbon cycling, and perhaps other microbially-driven functions, are markedly affected by the presence of root hairs.Utilizing maize root soil microcosms for studying soil zymography in the rhizosphere allowed to obtain soil samples from regions with distinct specific enzyme activities. In order to enhance the detection of actively metabolizing bacterial community members, we studied rRNA sequences and compared it to rRNA gene sequences from the same samples. Currently the data are under analysis.References(1) Wen, T-J, Schnable PS (1994) Analyses of mutants of three genes that influence root hair development in Zea mays (Gramineae) suggest that root hairs are dispensable. Am. J. Bot. 81, 833&#8211;842.(2) Szoboszlay M, Tebbe CC (2020) Hidden heterogeneity and co-occurrence networks of soil prokaryotic communities revealed at the scale of individual soil aggregates. Microbiol. Open, e1144. DOI: 10.1002/mbo3.1144(3) Vetterlein D et al. (2020) Experimental platforms for the investigation of spatiotemporal patterns in the rhizosphere &#8211; laboratory and field scale. J. Plant Nutr. Soil Sci., 000, 1&#8211;16 DOI: 10.1002/jpln.202000079

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Effects of Sunlight Exposure on Grapevine Powdery Mildew Development

Phytopathology ◽

10.1094/phyto-07-11-0205 ◽

2012 ◽

Vol 102 (9) ◽

pp. 857-866 ◽

Cited By ~ 24

Author(s):

Craig N. Austin ◽

Wayne F. Wilcox

Keyword(s):

Powdery Mildew ◽

Solar Radiation ◽

Controlled Environment ◽

Disease Development ◽

Inhibitory Effects ◽

Grapevine Powdery Mildew ◽

Individual Experiment ◽

Hyphal Formation ◽

The Individual ◽

Artificial Shading

Natural and artificially induced shade increased grapevine powdery mildew (Erysiphe necator) severity in the vineyard, with foliar disease severity 49 to 75% higher relative to leaves in full sun, depending on the level of natural shading experienced and the individual experiment. Cluster disease severities increased by 20 to 40% relative to those on check vines when ultraviolet (UV) radiation was filtered from sunlight reaching vines in artificial shading experiments. Surface temperatures of leaves in full sunlight averaged 5 to 8°C higher than those in natural shade, and in one experiment, filtering 80% of all wavelengths of solar radiation, including longer wavelengths responsible for heating irradiated tissues, increased disease more than filtering UV alone. In controlled environment experiments, UV-B radiation reduced germination of E. necator conidia and inhibited both colony establishment (hyphal formation and elongation) and maturity (latent period). Inhibitory effects of UV-B radiation were significantly greater at 30°C than at 20 or 25°C. Thus, sunlight appears to inhibit powdery mildew development through at least two mechanisms, i.e., (i) UV radiation's damaging effects on exposed conidia and thalli of the pathogen; and (ii) elevating temperatures of irradiated tissues to a level supraoptimal or inhibitory for pathogen development. Furthermore, these effects are synergistic at temperatures near the upper threshold for disease development.

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Combination Effects of Low Rates of Fluridone and Bentazon

Weed Technology ◽

10.1017/s0890037x00029390 ◽

1987 ◽

Vol 1 (2) ◽

pp. 168-170

Author(s):

J. P. Sterrett

Keyword(s):

Cirsium Arvense ◽

Growth Chamber ◽

Controlled Environment ◽

Cyperus Esculentus ◽

Canada Thistle ◽

Combination Effects ◽

Yellow Nutsedge ◽

Environment Chamber

The response of yellow nutsedge (Cyperus esculentusL. #3CYPES) and Canada thistle [Cirsium arvense(L.) Scop. # CIRAR] to combinations of low rates of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} and bentazon [3-(1-methylethyl)-(1H)-2,l,3-benzothiadiazin-4(3H)-one 2,2-dioxide] was determined in a controlled environment chamber and on Canada thistle in the field. In the growth chamber, injury to yellow nutsedge was increased with 24 g ai/ha fluridone combined with 323 g ai/ha bentazon. Either 2.7 or 5.4 g/ha fluridone combined with 27 g/ha bentazon caused uniform injury to Canada thistle. In the field, the combinations of 5.6 g/ha fluridone with either 28 or 2800 g/ha bentazon was phytotoxic to Canada thistle.

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