Phytophthora cinnamomi: Population Densities in Forest Soils

1977 ◽  
Vol 25 (5) ◽  
pp. 461 ◽  
Author(s):  
G Weste ◽  
P Ruppin
Keyword(s):  
Environmental Factors ◽  
Soil Water ◽  
Phytophthora Cinnamomi ◽  
Soil Water Potential ◽  
Forest Community ◽  
Population Densities ◽  
Sclerophyll Forest ◽  
Soil Temperatures ◽  
Disease Extension ◽  
Pathogen Populations

Population densities of Phytophthora cinnamomi, associated disease and environmental factors were studied concurrently during a 2-year period in three different forest ecosystems. Pathogen populations showed seasonal variation, low values being obtained for winter months associated with soil temperatures less than 10°C. Populations increased with warmer temperatures for spring and summer, but declined during dry periods in late summer or early autumn when the soil water potential was lower than -9 bars, although at that period soil temperatures were favourable. High populations were recorded in autumn, then declined with decrease in soil temperatures during winter. Correlation coefficients indicated a highly significant relationship between pathogen populations and soil temperatures from autumn to early summer, and between soil moisture and pathogen population for summer and autumn, in the Brisbane Ranges independently of site. The same pattern was evident in wetter forests at Narbethong and savannah woodlands at Wilson's Promontory, although results were not significant. Disease was evident wherever the pathogen occurred among susceptible hosts. The savannah woodland, the dry shrubby sclerophyll forest and the wetter sclerophyll forest all contained susceptible dominants; consequently disease was associated with changes in the forest community such as early death of the understorey, later die-back and death of the trees, and an increase in sedges and in bare ground. Symptoms and deaths increased with time from invasion. The severity of disease and its rate of extension, apart from spread by free water, were associated with environmental factors such as shallow soil, poor drainage and low soil water-holding capacity. These were characteristic of the Brisbane Ranges, where destruction of the forest community was severe and the rate of disease extension rapid. In the deep krasnozem at Narbethong and the deep sands of Wilson's Promontory, destruction was confined to the most susceptible hosts, disease extension was continuous but slow, and deaths occurred in a mosaic throughout the infected zone.

Phytophthora cinnamomi in the Brisbane Ranges: Patterns of Disease Extension

1976 ◽  
Vol 24 (2) ◽  
pp. 201 ◽  
Author(s):  
G Weste ◽  
P Ruppin ◽  
K Vithanage
Keyword(s):  
Environmental Factors ◽  
Phytophthora Cinnamomi ◽  
Soil Characteristics ◽  
Drainage Water ◽  
Sclerophyll Forest ◽  
Disease Extension ◽  
Wavy Boundary ◽  
Active Disease

Three patterns of disease extension were observed in areas of uncultivated shrubby dry sclerophyll forest invaded by the pathogen Phytophthora cinnamomi. Environmental factors were found to determine which pattern developed. Where inoculum was spread downhill with drainage water, diseased areas were separated by clearly defined boundaries from unaffected vegetation. Where disease extension occurred uphill through soil or from root to root, a wavy boundary marked the active disease front. Investigations showed that absence of disease extension for 4 years in highly susceptible vegetation may be associated with differences in soil characteristics.

Seasonal Variation in Numbers of Chlamydospores in Victorian Forest Soils Infected With Phytophthora cinnamomi

1978 ◽  
Vol 26 (5) ◽  
pp. 657 ◽  
Author(s):  
G Weste ◽  
K Vithanage
Keyword(s):  
Seasonal Variation ◽  
Soil Water ◽  
Forest Soils ◽  
Phytophthora Cinnamomi ◽  
Soil Water Potential ◽  
Native Forest ◽  
Forest Sites ◽  
Significant Seasonal Variation ◽  
Different Types ◽  
Soil Temperatures

Chlamydospore numbers were counted for 2 years on replicated soil samples from three different types of naturally infected Victorian native forest. Soil temperatures and soil water potentials were recorded concurrently. A highly significant seasonal variation in chlamydospore numbers was observed with maxima from summer to autumn and minima from winter to spring. There was little variation either between replicates or between different forest soils in winter and spring counts, but there was highly significant variation between different forest sites during the large summer and autumn counts. At this period sandy soil contained five to 12 times the number of chlamydo- spores found in other soils. For example, in autumn 1977,286 chlamydospores were recorded per 50 g sample from deep sandy soils compared with 31 for krasnozem and 17 for shallow duplex soils. At this period soil temperatures were similar but the soil water potential for the duplex soil was very low (-82 bars).

Microbial populations of three forest soils: seasonal variations and changes associated with Phytophthora cinnamomi

1977 ◽  
Vol 25 (4) ◽  
pp. 377 ◽  
Author(s):  
G Weste ◽  
K. Vithanage
Keyword(s):  
Forest Soils ◽  
Phytophthora Cinnamomi ◽  
Severe Disease ◽  
Organic Content ◽  
Microbial Populations ◽  
Garden Soil ◽  
Soil Temperatures ◽  
Disease Extension ◽  
Pathogen Populations ◽  
Soil Microbial Population

Microbial populations of three forest soils were assayed by a dilution plate procedure and compared with garden soil. The forest soils were selected from areas subjected to die-back disease caused by Phytophthora cinnamomi Rands, and were from sites for which pathogen populations, soil temperatures, rainfall and soil water potentials were concurrently recorded. Forest soils showed low microbial populations compared with garden soil. This was associated with low organic content, low nitrogen status and poor water-holding capacity. Areas with severe disease and rapid disease extension had a small soil microbial population, particuarly of actinomycetes, compared with soil from areas with moderate disease and slow disease extension. Microbial populations were lowest in spring and autumn when P. cinnamomi was most active, and zoospore production, dispersal and infection was maximal. Microbial populations of forest soil were reduced following die-back; and the reduction of disease was highly significant (P < 0.01) for the Brisbane Ranges where plant mortality was high and the percentage of bare ground increased.

A Model for Predicting Large Crabgrass (Digitaria sanguinalis) Emergence as Influenced by Temperature and Water Potential

Weed Science ◽  
1994 ◽  
Vol 42 (4) ◽  
pp. 561-567 ◽  
Author(s):  
Charles A. King ◽  
Lawrence R. Oliver
Keyword(s):  
Water Potential ◽  
Soil Water ◽  
Water Uptake ◽  
Field Experiments ◽  
Soil Water Potential ◽  
Lag Phase ◽  
Subsequent Increase ◽  
Soil Temperatures ◽  
Emergence Percentage ◽  
Large Crabgrass

Experiments were conducted to evaluate the influence of temperature and water potential on water uptake, germination, and emergence of large crabgrass in order to predict emergence in the field. Water uptake of seed soaked in polyethylene glycol solutions of 0 to −1400 kPa underwent an initial imbibition phase followed by a lag phase and subsequent increase in water content when radicles emerged from the seed. Maximum germination at 15 C was 12% at 0 kPa and 60% at 25 C at 0 to −200 kPa osmotic potential. In the growth chamber, large crabgrass emergence from soil began 2 to 3 d after planting at 30 or 35 C and within 9 to 10 d at 15 C. Maximum emergence of 77 % occurred at 25 C and at a soil water potential of −30 kPa. Emergence percentage decreased as water potential decreased or as temperature increased or decreased. A logistic equation described emergence of large crabgrass at each combination of temperature and soil water potential at which emergence occurred, and a predictive model was developed and validated by field data. In the field, there was little or no emergence at soil temperatures below 15 C or water potentials below −50 to −60 kPa. The model predicted the time of onset of large crabgrass emergence and the time to reach maximum emergence to within 2 to 4 d of that recorded in field experiments. The model also predicted the correct number of flushes of emergence occurring in the field in three of four experiments.

scholarly journals Robust Estimation of Absorbing Root Surface Distributions From Xylem Water Isotope Compositions With an Inverse Plant Hydraulic Model

2021 ◽  
Vol 4 ◽  
Author(s):  
Hannes P. T. De Deurwaerder ◽  
Marco D. Visser ◽  
Félicien Meunier ◽  
Matteo Detto ◽  
Pedro Hervé-Fernández ◽  
...  
Keyword(s):  
Environmental Factors ◽  
Soil Water ◽  
Robust Estimation ◽  
Inverse Modeling ◽  
Sap Flow ◽  
Soil Water Potential ◽  
Modeling Method ◽  
Flow Monitoring ◽  
Root Surfaces ◽  
Water Isotope

The vertical distribution of absorbing roots is one of the most influential plant traits determining plant strategy to access below ground resources. Yet little is known of natural variability in root distribution since collecting field data is challenging and labor-intensive. Studying stable water isotope compositions in plants could offer a cost-effective and practical solution to estimate the absorbing root surfaces distribution. However, such an approach requires developing realistic inverse modeling techniques that enable robust estimation of rooting distributions and associated uncertainty from xylem water isotopic composition observations. This study introduces an inverse modeling method that supports the assessment of the root allocation parameter (β) that defines the exponential vertical decay of a plants’ absorbing root surfaces distribution with soil depth. The method requires measurements obtained from xylem and soil water isotope composition, soil water potentials, and sap flow velocities when plants’ xylem water is sampled at a certain height above the rooting point. In a simulation study, we show that the approach can provide unbiased estimates of β and its associated uncertainty due to measuring errors and unmeasured environmental factors that can impact the xylem water isotopic data. We also recommend improving the accuracy and power of β estimation, highlighting the need for considering accurate soil water potential and sap flow monitoring. Finally, we apply the inverse modeling method to xylem water isotope data of lianas and trees collected in French Guiana. Our work shows that the inverse modeling procedure provides a robust analytical and statistical framework to estimate β. The method accounts for potential bias due to extraction errors and unmeasured environmental factors, which improves the viability of using stable water isotope compositions to estimate the distribution of absorbing root surfaces complementary to the assessment of relative root water uptake profiles.

Field Resistance in Three Native Monocotyledon Species That Colonize Indigenous Sclerophyll Forest After Invasion by Phytophthora cinnamomi

1984 ◽  
Vol 32 (4) ◽  
pp. 339 ◽  
Author(s):  
D Phillips ◽  
G Weste
Keyword(s):  
Phytophthora Cinnamomi ◽  
Lateral Roots ◽  
Fungal Growth ◽  
Field Resistance ◽  
Root Production ◽  
Root Tip ◽  
Bare Ground ◽  
Rapid Reduction ◽  
Sclerophyll Forest ◽  
Disease Extension

Lepidosperma laterale (Cyperaceae), Gahnia radula (Cyperaceae) and Poa sieberana (Poaceae) colonize bare ground of dry sclerophyll forest after disease due to P. cinnamomi. To determine their resistance, plants grown in divided root boxes were inoculated with 150-200 zoospores of the pathogen. Infected roots ceased growth. In the small necrotic lesions produced, the pathogen remained viable and capable of providing a source of inoculum for disease extension. Fungal growth was usually limited to the lesion but in some cases a few hyphae were observed in adjacent tissue. Away from the lesion there was a rapid reduction of fungal material and of the associated cellular disintegration. Rates of root production and root growth were not stimulated by infection but uninfected lateral roots replaced the root tip in some plants; in others, a new root tip emerged from the necrotic zone, enabling the plant to outgrow the fungal attack.

THE EFFECT OF SOIL WATER POTENTIAL, TEMPERATURE AND SEEDING DEPTH ON SEEDLING EMERGENCE OF WHEAT

1979 ◽  
Vol 59 (3) ◽  
pp. 259-264 ◽  
Author(s):  
R. DE JONG ◽  
K. F. BEST
Keyword(s):  
Water Potential ◽  
Soil Water ◽  
Minimum Temperature ◽  
Seedling Emergence ◽  
Potential Temperature ◽  
Soil Water Potential ◽  
Triticum Aestivum L ◽  
Planting Dates ◽  
Water Potentials ◽  
Soil Temperatures

Daily emergence counts were made on Canthatch wheat (Triticum aestivum L.) grown in five soil types, at four soil temperatures and three water potentials and planted at five different depths. Regardless of soil type, soil water potential or depth of planting, 50% emergence generally occurred within a week at 19.4 and 26.7 °C, and within 2 wk at 12.2 °C, but it took up to 6 wk at 5 °C. The heat sum required to attain 50% seedling emergence did not increase significantly with decreasing soil water potentials, but the minimum temperature for emergence dropped from 1.3 to 0.2 °C as the water potential decreased from −⅓ to −10 bar. It was suggested that the seedlings compensated for the increased water stress by lowering their minimum temperature requirements. Increasing the planting depth not only increased the heat requirement for emergence, but it also increased the variability of emergence, especially at low temperatures. Practical aspects concerning planting dates and depths were considered.

scholarly journals Orchard Groundcover Management Impacts on Soil Physical Properties

1994 ◽  
Vol 119 (2) ◽  
pp. 216-222 ◽  
Author(s):  
Ian A. Merwin ◽  
Warren C. Stiles ◽  
Harold M. van Es
Keyword(s):  
Soil Water ◽  
Soil Water Potential ◽  
Organic Matter Content ◽  
Matter Content ◽  
Water Infiltration ◽  
Soil Organic Matter Content ◽  
Water Capacity ◽  
Growing Seasons ◽  
Soil Temperatures

This study was conducted to compare various orchard groundcover management systems (GMSs)—including a crownvetch “living mulch” (CNVCH), close-mowed (MWSOD) and chemically growth-regulated (GRSOD) sodgrasses, pre-emergence (NDPQT) and two widths of post-emergence (GLY1.5 and GLY2.5) herbicides, hay-straw mulch (STMCH), and monthly rototillage (tilled)—during the first 6 years in a newly established apple (Malus domestica Borkh.) planting. Mean soil water potential at 5 to 35 cm deep varied substantially among treatments each summer, and treatment × year interactions were observed. During most growing seasons from 1986 to 1991, soil water availability trends were STMCH > NDPQT > GLY2.5 > GLY1.5 > tilled > GRSOD > MWSOD > CNVCH. Soil organic matter content increased under STMCH, CNVCH, and MWSOD and decreased under NDPQT and tilled treatments. Water infiltration and saturated hydraulic conductivity after 4 years were lower under NDPQT and tilled, and soil under STMCH and GRSOD retained more water per unit volume at applied pressures approximating field water capacity. Mid-summer soil temperatures at 5 cm deep were highest (25 to 28C) in tilled and NDPQT plots, intermediate (22 to 24C) under GRSOD, and lowest (16 to 20C) under CNVCH and STMCH. These observations indicate that long-term soil fertility and orchard productivity may be diminished under pre-emergence herbicides and mechanical cultivation in comparison with certain other GMSs.

Factors Affecting the Population Density of Phytophthora cinnamomi in Native Forests of the Brisbane Ranges, Victoria.

1975 ◽  
Vol 23 (1) ◽  
pp. 77 ◽  
Author(s):  
G Weste ◽  
P Ruppin
Keyword(s):  
Phytophthora Cinnamomi ◽  
Ground Cover ◽  
Wood Production ◽  
Population Densities ◽  
Pathogen Population ◽  
Recent Infection ◽  
Factors Affecting ◽  
Disease Extension ◽  
Open Woodland

Population densities of Phytophthora cinnamomi Rands were measured at 10-day intervals during a period of 13 months at three sites in the Brisbane Ranges. Statistical analyses of results and of simultaneous metereological measurements demonstrated that both low temperatures and dry soils were correlated with a significant decrease in pathogen population. Disease extension occurred uphill on a slope of 4" at 6 . 6 m per year, but only from recent infection. Population densities of older sites were significantly less than that of the new site and no measurable disease extension occurred uphill from them. Disease caused an immediate and continuing reduction in understorey in both the number of species and the ground cover and, in the long term, a reduction in both wood production and the number of trees as the dense dry sclerophyll shrubby forest was changed to an open woodland.

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