Development of Phytophthora cinnamomi Infection in Roots of Eucalypt Species Growing in a Soil That Suppresses Phytophthora Root Disease

1983 ◽  
Vol 31 (3) ◽  
pp. 239 ◽  
Author(s):  
GC Marks ◽  
IW Smith
Keyword(s):  
Inner Core ◽  
Phytophthora Cinnamomi ◽  
Sandy Loam ◽  
Seedling Survival ◽  
Genetic Resistance ◽  
Coarse Sand ◽  
Root Disease ◽  
Phenotypic Resistance ◽  
Eucalypt Species ◽  
Core Soil

When Eucalyptus sieberi was grown in either a steamed or unsteamed krasnozem that suppressed Phytophthora cinnamomi root rot and repotted when either 6 or 12 weeks old in a larger container of inoculated sandy loam, seedling survival was significantly greater in the unsteamed treatments. By varying the treatments in the inner core soil and outer inoculum jacket, substituting a biologically inert coarse sand in place of the krasnozem in the core, and using eucalypt species of varying disease tolerance while maintaining very strict hygiene conditions throughout these experiments, it was possible to either demonstrate or deduce that: (a) the seedlings were killed when infection spread into the major roots, root collar and lower stem; (b) the microflora in the unsteamed krasnozem appeared to slow down the decay process within the root, possibly when the fungus was attempting to establish itself within the root; (c) the phenotypic resistance of a seedling to root disease depended, inter alia, on its genetic resistance and on the microflora in the surrounding soil; (d) once the fungus was established in the suberized tissues the microflora in the external environment had no influence on disease.

Determination of water content in drying soils: incorporating transition from liquid phase to vapour phase

Soil Research ◽  
2004 ◽  
Vol 42 (1) ◽  
pp. 1 ◽  
Author(s):  
F. Konukcu ◽  
A. Istanbulluoglu ◽  
I. Kocaman
Keyword(s):  
Water Content ◽  
Transition Zone ◽  
Sandy Loam ◽  
Vapour Phase ◽  
Coarse Sand ◽  
Arid Environments ◽  
Evaporation Front ◽  
Matric Potential ◽  
Silty Loam

In arid and semi-arid environments, soil profiles often exhibit a liquid–vapour displacement known as evaporation front characterised by a critical matric potential (ψme) or water content (θe) located somewhere inside the unsaturated zone above a watertable (WT). The objective of this study was to determine the θe including the range of water content (θ) in the transition zone from liquid to vapour both theoretically and experimentally for different soil textures under saline and non-saline WTs. Characteristic shapes of water content and salt concentration profiles were the criteria to obtain θe experimentally, and the θ–diffusivity relationship was used to compute the θe and θ range in the transition zone. Measured θe values of 0.05 and 0.12 m3/m3 under non-saline WT and 0.07 and 0.15 m3/m3 under saline WT were in agreement with the computed values of 0.05 and 0.10 m3/m3 for sandy loam and clay loam soils, respectively. The model calculates roughly the same θe for saline and non-saline conditions. Besides experimental soils, θe and range of θ in the transition zone were calculated for silty loam and coarse sand. The lighter the soil texture, the smaller is θe and the steeper the transition zone. The results were further compared with those calculated by different authors.

Rate of Disease Development in Eucalyptus sieberi Growing in Suppressive Soils Inoculated With Phytophthora cinnamomi

1985 ◽  
Vol 33 (2) ◽  
pp. 159 ◽  
Author(s):  
GC Marks ◽  
IW Smith
Keyword(s):  
Post Infection ◽  
Phytophthora Cinnamomi ◽  
Inoculum Density ◽  
Disease Development ◽  
The Core ◽  
Development Rates ◽  
Core Soil ◽  
Compound Interest ◽  
Root Collar

The rate at which root collar infection, caused by Phytophthora cinnamomi Rands, developed in Eucalyptus sieberi L. Johnson was tested by growing 40, 6-month-old seedlings in cores of disease- suppressive (DSS) krasnozem-type soil that had either been treated or not treated with steam. The core soil was inoculated by repotting the seedlings in a jacket of steamed or unsteamed sand or krasnozem that had been mixed with a mycelium-chlamydospore suspension. Disease development was of the compound interest type (sens. Van der Plank) and was slower in unsteamed DSS core soils. Inoculum density (ID) increased more than 10 times at the end of all tests, and the time taken for collar infection to appear was shortened when the inoculum was mixed with unsteamed DSS. The fungus was isolated more frequently from the collar of seedlings growing in steam-treated than in unsteamed DSS. The results showed that the soil used was only mildly disease-suppressive and suggest that post- infection antagonism may be the cause of slower disease development rates in DSS. Introduction

Evaluation of gypsum and organic matter additions for improving soil structure in a radiata pine nursery at Benalla, Victoria

1983 ◽  
Vol 23 (121) ◽  
pp. 208 ◽  
Author(s):  
DW Flinn ◽  
RJ Waugh
Keyword(s):  
Organic Matter ◽  
Seedling Survival ◽  
Clay Content ◽  
Radiata Pine ◽  
Fertilizer Application ◽  
Coarse Sand ◽  
Soil Conditions ◽  
Infiltration Capacity ◽  
Pine Seedlings ◽  
Block Experiment

A randomized block experiment was carried out in a radiata pine nursery at Benalla where the soil is weakly aggregated and slakes severely on wetting. Sunflower hulls or sudax ST6 hay or gypsum/dolomite were added during one cycle of a summer green crop, winter cover crop and a pine crop. Plots were also split for a deep ripping treatment. The aim was to improve soil conditions for the growth of pine seedlings. The addition of 170 t/ha of sunflower hulls reduced bulk density (P<0.01) and surface crust resistance (P< 0.05) and markedly increased infiltration capacity (P<0.01). Water-stable aggregation was not statistically affected by any of the treatments because the soil has a clay content of only 18%, though there was an encouraging trend of more water-stable aggregates within the size range 0.25-2 mm following the application of sunflower hulls. Germination of the pine crop was unaffected by treatments as the seed was covered with coarse sand. Seedling survival was low (range 41.1 -47.6%), due in part to saline conditions following fertilizer application. Early growth of seedlings was greater (P<0.05) where additional organic matter was incorporated, but differences between treatments were not statistically significant at harvest. We conclude that soil conditions can be improved for pine growth by adding a large quantity of organic matter, reducing cultivation and maintaining an intensive green cropping program.

scholarly journals Resistance toPhytophthora cinnamomiin American Chestnut (Castanea dentata) Backcross Populations that Descended from Two Chinese Chestnut (Castanea mollissima) Sources of Resistance

Plant Disease ◽  
2019 ◽  
Vol 103 (7) ◽  
pp. 1631-1641 ◽  
Author(s):  
Jared W. Westbrook ◽  
Joseph B. James ◽  
Paul H. Sisco ◽  
John Frampton ◽  
Sunny Lucas ◽  
...  
Keyword(s):  
Phytophthora Cinnamomi ◽  
Seedling Survival ◽  
Cryphonectria Parasitica ◽  
Castanea Dentata ◽  
American Chestnut ◽  
Chestnut Blight ◽  
Sources Of Resistance ◽  
Backcross Population ◽  
Chinese Chestnut ◽  
Root Health

Restoration of American chestnut (Castanea dentata) depends on combining resistance to both the chestnut blight fungus (Cryphonectria parasitica) and Phytophthora cinnamomi, which causes Phytophthora root rot, in a diverse population of C. dentata. Over a 14-year period (2004 to 2017), survival and root health of American chestnut backcross seedlings after inoculation with P. cinnamomi were compared among 28 BC3, 66 BC4, and 389 BC3F3families that descended from two BC1trees (Clapper and Graves) with different Chinese chestnut grandparents. The 5% most resistant Graves BC3F3families survived P. cinnamomi infection at rates of 75 to 100% but had mean root health scores that were intermediate between resistant Chinese chestnut and susceptible American chestnut families. Within Graves BC3F3families, seedling survival was greater than survival of Graves BC3and BC4families and was not genetically correlated with chestnut blight canker severity. Only low to intermediate resistance to P. cinnamomi was detected among backcross descendants from the Clapper tree. Results suggest that major-effect resistance alleles were inherited by descendants from the Graves tree, that intercrossing backcross trees enhances progeny resistance to P. cinnamomi, and that alleles for resistance to P. cinnamomi and C. parasitica are not linked. To combine resistance to both C. parasitica and P. cinnamomi, a diverse Graves backcross population will be screened for resistance to P. cinnamomi, survivors bred with trees selected for resistance to C. parasitica, and progeny selected for resistance to both pathogens will be intercrossed.

Relationship of rainfall, cultural practices, soil and plant nutrients, and seedling survival with root disease and parasitic nematode numbers in annual Medicago spp. Pastures

1999 ◽  
Vol 50 (6) ◽  
pp. 977 ◽  
Author(s):  
M. P. You ◽  
I. T. Riley ◽  
K. Sivasithamparam ◽  
M. J. Barbetti
Keyword(s):  
Root Rot ◽  
Lateral Root ◽  
Cultural Practices ◽  
Seedling Survival ◽  
Root Disease ◽  
Plant Nutrients ◽  
Tap Root ◽  
Low Levels ◽  
Annual Medicago ◽  
Relationship Of

Surveys were conducted for annual Medicago spp. (medic) pastures in the grain belt of south-west Western Australia during spring 1996 and winter–spring 1997 to determine the relationship of rainfall, cultural practices, soil and plant nutrients, and seedling survival with severity of root disease and numbers of parasitic nematodes. Medic pasture was sampled on 116 farms. Most pastures consisted of a single medic variety, viz. Serena, Santiago, Cyprus, or Caliph, whereas about 33% of sites had mixed varieties. Regression analyses showed that high rainfall and application of phosphorus fertilisers were correlated with increased severity of rot in medic tap roots. Crop history and medic variety were not related to the level of root rot. Numbers of Pratylenchusin medic roots were not correlated with the level of tap or lateral root rot, medic variety, rainfall, or with the application of insecticide, fertilisers, or herbicides. Soil with relatively high levels of P, NO3-, or Fe was associated with an increased level of tap root rot. Soils with high pH were associated with reduced tap root rot. Soils with relatively high K were related to severe lateral root rot, whereas relatively high levels of P in soil were associated with reduced lateral root rot. Plants with high levels of tap root rot showed low levels of Mg, whilst low levels of Ca and NO3– in tissues were related to high levels of lateral root rot. High levels of tap root rot were associated with relatively high levels of total N, K, and S, Cu, Zn, Mn, and NO3- in plant tissues. Plants with relatively high levels of lateral root rot had relatively high levels of Cu in shoots. Of the 116 annual Medicago pastures sampled, only 1% had adequate Mg content and only 19% had adequate Ca content. However, 83% had higher than adequate levels of Cu, 70% had higher than adequate levels of Mn, and all samples showed more than adequate levels of chloride. Experimental sites of M. polymorpha cv. Serena at 6 farms showed that the percentage survival rate of seedlings was negatively correlated with the severity of tap and lateral root rot in the previous year. These results indicate that in the farms surveyed there is a serious threat to annual medic pastures from root rot fungi. The severity of the disease was partly determined by soil conditions and cultural practices.

Effect of soil properties and soil disturbance on frost heaving of mineral soil: a laboratory experiment

2006 ◽  
Vol 36 (11) ◽  
pp. 2885-2893 ◽  
Author(s):  
Michelle de Chantal ◽  
Hannu Rita ◽  
Urban Bergsten ◽  
Mikaell Ottosson Löfvenius ◽  
Harald Grip
Keyword(s):  
Laboratory Experiment ◽  
Repeated Measures ◽  
Sandy Loam ◽  
Mineral Soil ◽  
Fine Sand ◽  
Soil Disturbance ◽  
Coarse Sand ◽  
Loamy Sand ◽  
Frost Heaving ◽  
C And N

A laboratory experiment was done to identify the properties that make a substrate susceptible to frost heaving. Tests were carried out on nondisturbed soil cores (fresh and dry) of Ae and B horizons from sand, loamy sand, and sandy loam in a freezing cabinet (–3.5 °C). Cores were continuously supplied with water from below. Freezing tests were repeated after soil disturbance (V-shaped furrow, 50% increase in surface area). The effects of texture, horizon, drying, and disturbance on frost heaving were tested using repeated-measures analysis of variance with soil elements (organic Al, organic Fe, inorganic Al, inorganic Fe, C, and N) and soil fractions (clay, fine silt, coarse silt, fine sand, and coarse sand) as covariates. The effect of horizon was as important as that of texture, and soil disturbance increased frost heaving. Disturbed fresh B horizon from loamy sand and sandy loam heaved the most (soil expansion >5% in height), whereas nondisturbed dry Ae horizon, regardless of texture, and nondisturbed dry B horizon from sand heaved the least (soil expansion <0.8% in height). Soil elements and fractions had an impact on frost heaving, especially organic Al, although it was of a smaller magnitude. Therefore, it is suggested that seedbeds or planting substrates be prepared by exposing the nondisturbed Ae horizon only, that is, without exposing or disturbing the B horizon.

Sulfonylurea herbicides applied to acidic sandy soils: a bioassay for residues and factors affecting recoveries

1991 ◽  
Vol 42 (7) ◽  
pp. 1205 ◽  
Author(s):  
WM Blacklow ◽  
WM Blacklow ◽  
PC Pheloung ◽  
PC Pheloung
Keyword(s):  
Half Life ◽  
Lens Culinaris ◽  
Sandy Loam ◽  
Crop Protection ◽  
Coarse Sand ◽  
Cereal Crop ◽  
Minimum Concentration ◽  
Factors Affecting ◽  
White Sand ◽  
Plastic Bags

Chlorsulfuron and triasulfuron, applied at 15-35 g ha-1, are a challenge to analytical methods because residues are phytotoxic at concentrations of pg kg-1 soil. A bioassay based on the suppression of root growth of lentils (Lens culinaris cv. Laird) can detect a minimum concentration of 0.48g kg-1 soil. The sandy loam, 20g, is extracted with methanol and extracts are made up in 5 mM CaCl2. The extracts, 20 mL, are added to 250 g of coarse white sand in plastic cups and sown with seven pre-germinated lentil seeds. The cups are enclosed in plastic bags to prevent evaporation, and incubated for 6 days at 20�C. Herbicide concentrations are brought within the range of sensitivity of the bioassay by dilutions of the extracts. The assay was easier, and more sensitive, precise and reproducible than a direct assay of soil. Herbicides in the field were lost due to photolysis (38-49% in 8 h) and in laboratory manipulations by hydrolysis with high pH extractants, such as saturated Ca(OH)2 (pH 11.2) where the half-life was about 4 h. Hydrolysis at the pH of the sandy loam and the bioassay in coarse sand, pH 5 - 8, gave a half-life of 176 and 198 days for chlorsulfuron and triasulfuron, respectively, at 20�C; at 30�C, the corresponding half-lives were 47 and 27 days. At concentrations for 50% suppressions of lentil roots (ID50 = 0.6 8g L-1 in coarsesand), adsorption in the sandy loam, estimated by the Langmuir equation, was 76% of the total residues of both herbicides. Adsorption could account for the differences in the ID50 of lentils grown in sandy loam and coarse sand for triasulfuron, but it was overcorrected for chlorsulfuron. The herbicides should be applied as near to seeding the cereal crop as possible and should be incorporated with the seeding operation so that losses from photolysis and hydrolysis in warm acidic soils are minimized before crop protection is needed.

scholarly journals Determination of the Boundaries of the Compressible Strata When Conducting Engineering Surveys

2020 ◽  
Vol 24 (3) ◽  
pp. 79-87
Author(s):  
K. O. Dubrakova ◽  
V. A. Solodilova
Keyword(s):  
Sandy Loam ◽  
Physical And Mechanical Properties ◽  
Fine Sand ◽  
Coarse Sand ◽  
Adequate Accuracy ◽  
Practical Standpoint ◽  
The Cost ◽  
The Given ◽  
Main Influence

Purpose of research. Errors and inaccuracies in the preparation of deliverables based on the results of engineering surveys which are an integral and important part of the design and estimate documentation, can lead to irreversible consequences and significantly reduce the life of buildings and structures. The main difficulty in investigating soil physical and mechanical properties at a construction site is to determine the depth of excavation. This is due to the fact that an increase in the calculated depth leads to the increase in the cost of work, and its decrease leads to the risk of inaccuracies and errors in the design of foundations of buildings and structures. In accordance with the current regulatory documents, the excavation depth during soil investigation should be 1-2 meters below the boundary of the compressible strata. The condition on the basis of which the specified boundary is determined is provided. The development of a technique that allows determining the depth of the compressible strata at the stage of engineering surveying with adequate accuracy is an important task from a practical standpoint. Methods. Determining natural stress Ϭzg,0 as the product of foundation depth d and the specific gravity of the soil above the base ɣ′ІІ,  , taking into account the fact that the average pressure tends to the value of the estimated resistance of the soil, it is shown that physical-mechanical structure of the base soil exerts the main influence on the parameters of the compressible strata, and correspondingly, to the excavation depth value. In this case, the stresses transferred by the foundation of a building or structure have an indirect effect. Results. The maximum values of the depth of excavation for engineering and geological surveying for tight coarse sand, medium density and fineness sand, and fine sand and sandy loam are determined. Conclusion. It is concluded that the given technique allows determining the depth of excavation during engineering and geological surveying with an adequate accuracy.

scholarly journals Individual bacteria in structured environments rely on phenotypic resistance to phage

PLoS Biology ◽  
2021 ◽  
Vol 19 (10) ◽  
pp. e3001406
Author(s):  
Erin L. Attrill ◽  
Rory Claydon ◽  
Urszula Łapińska ◽  
Mario Recker ◽  
Sean Meaden ◽  
...  
Keyword(s):  
Genetic Resistance ◽  
Natural Environments ◽  
Bacterial Survival ◽  
Phenotypic Resistance ◽  
Bacterial Response ◽  
Modelling Framework ◽  
Planktonic Bacteria ◽  
Phage Dna ◽  
Phage Receptor

Bacteriophages represent an avenue to overcome the current antibiotic resistance crisis, but evolution of genetic resistance to phages remains a concern. In vitro, bacteria evolve genetic resistance, preventing phage adsorption or degrading phage DNA. In natural environments, evolved resistance is lower possibly because the spatial heterogeneity within biofilms, microcolonies, or wall populations favours phenotypic survival to lytic phages. However, it is also possible that the persistence of genetically sensitive bacteria is due to less efficient phage amplification in natural environments, the existence of refuges where bacteria can hide, and a reduced spread of resistant genotypes. Here, we monitor the interactions between individual planktonic bacteria in isolation in ephemeral refuges and bacteriophage by tracking the survival of individual cells. We find that in these transient spatial refuges, phenotypic resistance due to reduced expression of the phage receptor is a key determinant of bacterial survival. This survival strategy is in contrast with the emergence of genetic resistance in the absence of ephemeral refuges in well-mixed environments. Predictions generated via a mathematical modelling framework to track bacterial response to phages reveal that the presence of spatial refuges leads to fundamentally different population dynamics that should be considered in order to predict and manipulate the evolutionary and ecological dynamics of bacteria–phage interactions in naturally structured environments.

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