Population Densities ofPhytophthora capsiciin Field Soils in Relation to Drip Irrigation, Rainfall, and Disease Incidence

Plant Disease ◽  
1992 ◽  
Vol 76 (10) ◽  
pp. 1017 ◽  
Author(s):  
Jean B. Ristaino
Keyword(s):  
Drip Irrigation ◽  
Disease Incidence ◽  
Population Densities ◽  
Field Soils

The relation of population densities of the antagonist, Laetisaria arvalis, to seedling diseases of table beet incited by Pythium ultimum

1986 ◽  
Vol 32 (2) ◽  
pp. 156-159 ◽  
Author(s):  
S. Bruce Martin ◽  
G. S. Abawi ◽  
H. C. Hoch
Keyword(s):  
Low Temperature ◽  
Population Density ◽  
Disease Incidence ◽  
Pythium Ultimum ◽  
Quadratic Model ◽  
Damping Off ◽  
Population Densities ◽  
Field Soils ◽  
Laetisaria Arvalis ◽  
The Relationship

Sclerotia of Laetisaria arvalis were added to raw or steamed table beet field soils infested with Pythium ultimum and other low-temperature Pythium spp. to determine the relationship between soil population densities of the antagonist to disease incidence. Decrease in disease incidence of table beet seedlings and final Pythium spp. inoculum densities were linearly related to increasing population density of the antagonist in raw field soils. In P. ultimum infested steamed soils, decreasing disease incidence was also related to increasing population densities of L. arvalis, but the relationship was curvilinear and was described by a quadratic model. The latter models also described the decrease in P. ultimum inoculum densities with increasing levels of the antagonist. Percentages of healthy plants (those surviving the pre- and post-emergence damping-off disease phases) were increased approximately 20% in raw soils containing 100 sclerotia of L. arvalis per gram soil in comparison with those of unamended soils. However, in Pythium infested steamed soils, percentages of healthy plants in soil amended with 100 sclerotia of L. arvalis per gram soil were increased by 40–60%.

scholarly journals Holdover Inoculum of Pseudomonas syringae pv. alisalensis from Broccoli Raab Causes Disease in Subsequent Plantings

Plant Disease ◽  
2006 ◽  
Vol 90 (8) ◽  
pp. 1077-1084 ◽  
Author(s):  
N. A. Cintas ◽  
S. T. Koike ◽  
R. A. Bunch ◽  
C. T. Bull
Keyword(s):  
Pseudomonas Syringae ◽  
Brassica Rapa ◽  
Bacterial Blight ◽  
Laboratory Tests ◽  
Bacterial Population ◽  
Disease Incidence ◽  
Untreated Soil ◽  
Bacterial Populations ◽  
Field Soils ◽  
Over Time

Uniform plots of broccoli raab (Brassica rapa subsp. rapa) seedlings were inoculated with a rifampicin-resistant strain of Pseudomonas syringae pv. alisalensis, the causal agent of bacterial blight on crucifers, resulting in 100% disease incidence in mature plants. Diseased plants were incorporated into the soil at maturity and smaller replicated plots were replanted at various times after incorporation. Rifampicin-resistant fluorescent pseudomonads with rep-PCR profiles identical to P. syringae pv. alisalensis were isolated from lesions on plants grown in soil into which the first diseased crop was incorporated. Disease incidence declined in mature plants as the length of time between incorporation of the first planting and seeding of the replanted plots increased. Bacterial population levels in soil decreased over time and bacteria were no longer detectable 3 weeks after incorporation of the diseased crop. In laboratory tests, population levels of P. syringae pv. alisalensis decreased in untreated soil but not in autoclaved soil. Greenhouse studies demonstrated a direct correlation between population levels of P. syringae pv. alisalensis applied to soil and disease incidence in seedlings. However, the decline in bacterial populations in field soils did not wholly account for the decline in disease incidence with subsequent plantings.

scholarly journals Distribution of Phytophthora spp. in Field Soils Determined by Immunoassay

1997 ◽  
Vol 87 (1) ◽  
pp. 101-107 ◽  
Author(s):  
S. A. Miller ◽  
L. V. Madden ◽  
A. F. Schmitthenner
Keyword(s):  
Disease Incidence ◽  
Detection Threshold ◽  
Threshold Value ◽  
Enzyme Linked Immunosorbent Assay ◽  
Field Sampling ◽  
Phytophthora Blight ◽  
Phytophthora Root Rot ◽  
Soybean Field ◽  
Phytophthora Spp ◽  
Field Soils

Populations of Phytophthora spp. were determined by enzyme-linked immunosorbent assay (ELISA) in field soils used for pepper and soybean production in Ohio. Soybean fields were sampled extensively (64 fields, n = 6 samples per field over 2 years) and intensively (4 fields, n = 64 samples per field in 1 year) to assess heterogeneity of P. sojae populations. Four pepper fields (n = 64), three of which had a history of Phytophthora blight (caused by P. capsici), also were sampled intensively during a 6-month period. Mean (m), variance (v), and measures of aggregation (e.g., variance-to-mean ratio [v/m]) of immunoassay values, translated to Phytophthora antigen units (PAU), were related to the disease history in each of the pepper and soybean fields. Mean PAU values for fields in which Phytophthora root rot (soybean) or blight (pepper) had been moderate to severe were higher than in fields in which disease incidence had been low or not observed. A detection threshold value of 11.3 PAU was calculated with values for 64 samples from one pepper field, all of which tested negative for Phytophthora by bioassay and ELISA. Seven of the eight intensively sampled fields contained at least some detectable Phytophthora propagules, with the percentage of positive samples ranging from 1.6 to 73.4. Mean PAU values ranged from 1 to 84 (extensive soybean field sampling), 6 to 24 (intensive soybean field sampling), and 4 to 30 (intensive pepper field sampling); however, variances ranged from 0 to 7,774 (extensive sampling), 30 to 848 (intensive soybean field sampling), and 5 to 2,401 (intensive pepper field sampling). Heterogeneity of PAU was high in most individual soybean and pepper fields, with values of v/m greater than 1, and log(v) increasing with log(m), with a slope of about 2.0. Spatial autocorrelation coefficients were not significant, indicating there was no relationship of PAU values in neighboring sampling units (i.e., field locations) of the intensively sampled fields. Combined results for autocorrelations and v/m values indicate that Phytophthora was highly aggregated in these fields but that the scale of the aggregation (e.g., average focus size) was less than the size of the sampling units. Because of the observed variability, we calculated that sample sizes of 20 or more would be needed to estimate precisely the mean density of Phytophthora in most cases.

scholarly journals Effects of Crop Rotation and Irrigation on Verticillium dahliae Microsclerotia in Soil and Wilt in Cauliflower

1998 ◽  
Vol 88 (10) ◽  
pp. 1046-1055 ◽  
Author(s):  
C. L. Xiao ◽  
K. V. Subbarao ◽  
K. F. Schulbach ◽  
S. T. Koike
Keyword(s):  
Verticillium Wilt ◽  
Verticillium Dahliae ◽  
Drip Irrigation ◽  
Disease Incidence ◽  
Subsurface Drip Irrigation ◽  
Irrigation Methods ◽  
Irrigation Regimes ◽  
Subsurface Drip ◽  
Field Plots ◽  
Plot Design

Experiments were conducted in field plots to evaluate the effects of broccoli residue on population dynamics of Verticillium dahliae in soil and on Verticillium wilt development on cauliflower under furrow and subsurface-drip irrigation and three irrigation regimes in 1994 and 1995. Treatments were a factorial combination of three main plots (broccoli crop grown, harvested, and residue incorporated in V.dahliae-infested plots; no broccoli crop or residue in infested plots; and fumigated control plots), two subplots (furrow and subsurface-drip irrigation), and three sub-subplots (deficit, moderate, and excessive irrigation regimes) arranged in a split-split-plot design with three replications. Soil samples collected at various times were assayed for V. dahliae propagules using the modified Anderson sampler technique. Incidence and severity of Verticillium wilt on cauliflower were assessed at 7- to 10-day intervals beginning a month after cauliflower transplanting and continuing until harvest. Number of propagules in all broccoli plots declined significantly (P < 0.05) after residue incorporation and continued to decline throughout the cauliflower season. The overall reduction in the number of propagules after two broccoli crops was approximately 94%, in contrast to the fivefold increase in the number of propagules in infested main plots without broccoli after two cauliflower crops. Disease incidence and severity were both reduced approximately 50% (P < 0.05) in broccoli treatments compared with no broccoli treatments. Differences between furrow and subsurface-drip irrigation were not significant, but incidence and severity were significantly (P < 0.05) lower in the deficit irrigation regime compared with the other two regimes. Abundance of microsclerotia of V. dahliae on cauliflower roots about 8 weeks after cauliflower harvest was significantly (P < 0.05) lower in treatments with broccoli compared with treatments without broccoli. Rotating broccoli with cauliflower and incorporating broccoli residues into the soils is a novel means of managing Verticillium wilt on cauliflower and perhaps on other susceptible crops. This practice would be successful regardless of the irrigation methods or regimes followed on the susceptible crops.

scholarly journals Use of Chemical Flocculation and Nested PCR for Heterodera glycines Detection in DNA Extracts from Field Soils with Low Population Densities

Plant Disease ◽  
2017 ◽  
Vol 101 (7) ◽  
pp. 1153-1161 ◽  
Author(s):  
Richard Baidoo ◽  
Guiping Yan ◽  
Berlin Nelson ◽  
Andrea M. Skantar ◽  
Senyu Chen
Keyword(s):  
Nested Pcr ◽  
Soybean Cyst Nematode ◽  
Heterodera Glycines ◽  
Nematode Species ◽  
Field Soil ◽  
Population Densities ◽  
Pcr Assay ◽  
Soil Dna ◽  
Pcr Inhibitor ◽  
Field Soils

The soybean cyst nematode (SCN) Heterodera glycines is a major pathogen of soybean worldwide. Distinction between SCN and other members of the H. schachtii sensu stricto group based on morphology is a tedious task. A molecular assay was developed to detect SCN in field soils with low population densities and to differentiate SCN from other species. Various numbers of SCN eggs or juveniles were inoculated into 10 g of sterilized soil from which soil DNA was extracted using the PowerSoil DNA Isolation Kit. A specific amplicon was amplified using published SCN-specific primers SCNF1/SCNR1. This primer set was evaluated for the first time to detect SCN directly in soil DNA extracts. The specificity of the primers was confirmed by testing 36 isolates of other nematode species. The PCR assay detected one SCN egg or juvenile added to 10 g of soil. The assay was validated using 35 field soil samples. Grinding the field soil coupled with PCR inhibitor removal by AlNH4(SO4)20.12H2O treatment of soil DNA extracts followed by nested PCR enabled SCN detection as low as 12 SCN eggs/200 g soil. The PCR assay not only provides a sensitive method for SCN detection at low densities but also provides a discrimination method for SCN from other closely related nematodes.

scholarly journals Distribution of Lettuce Big-Vein Incidence Under Three Irrigation Systems

Plant Disease ◽  
2014 ◽  
Vol 98 (2) ◽  
pp. 206-212
Author(s):  
J. J. Hao ◽  
K. V. Subbarao
Keyword(s):  
Drip Irrigation ◽  
Disease Incidence ◽  
Sprinkler Irrigation ◽  
Distribution Patterns ◽  
Subsurface Drip Irrigation ◽  
Healthy Plant ◽  
Distribution Analysis ◽  
Irrigation Systems ◽  
Vector Distribution ◽  
Subsurface Drip

Spatial patterns of lettuce big-vein (LBV) incidence under furrow, sprinkler, and subsurface drip irrigation systems were determined. Because LBV pathogen is a virus and is vectored by the soilborne chytrid Olpidium brassicae, different irrigation systems likely affect the movement of the vector and were hypothesized to result in different distribution patterns and levels of the disease. Lettuce plants were mapped by recording the location of each LBV-infected or healthy plant in arbitrarily selected plots of sizes 16 by 30, 20 by 30, and 18 by 50 m in Salinas, Gonzales, and Santa Maria in California. Data were arrayed into different quadrat sizes by rearrangement, and disease incidence was calculated for each quadrat. Frequency distribution analysis and spatial autocorrelation analyses were performed on this data. LBV incidence was aggregated in all furrow-irrigated fields, four of five subsurface drip-irrigated fields, and two of three sprinkler-irrigated fields. The remaining fields had a random distribution. As the quadrat size increased, index of aggregation decreased, and vice versa. In fields under sprinkler irrigation, regardless of whether the spatial pattern of LBV was random or aggregated, no directional orientation occurred. However, under furrow or subsurface drip irrigation, the aggregation mostly occurred across the rows. Although irrigation type influenced LBV distribution pattern and incidence in lettuce fields, the differential effects of irrigation type on vector O. brassicae could not be discerned in this study. The sprinkler irrigation practiced in lettuce production until thinning may influence the vector distribution and the subsequent irrigation methods adapted for the remainder of the season in individual fields may play a significant role in disease incidence.

Morphological, pathogenic and molecular characterization of Phoma spp. isolated from onion field soils in Puerto Rico.

1969 ◽  
Vol 92 (1-2) ◽  
pp. 73-86 ◽  
Author(s):  
Ismael E. Badillo-Vargas ◽  
Lydia I. Rivera-Vargas ◽  
Juan Calle-Bellido
Keyword(s):  
Puerto Rico ◽  
Disease Incidence ◽  
Its Region ◽  
Restriction Enzymes ◽  
Molecular Characteristics ◽  
Base Pairs ◽  
Rdna Its ◽  
Field Soils ◽  
Rdna Its Region

Thirteen Phoma spp. isolates collected during a survey conducted in onion field soils in Santa Isabel, Puerto Rico, were examined on the basis of morphology, pathogenicity and molecular characteristics. Twelve isolates were identified as Phoma putaminum Speg. and one isolate as an atypical Phoma macrostoma var. incolorata (section Phyllostictoides).This is the first report of P. putaminum and P. macrostoma var. incolorata for Puerto Rico and the Caribbean. In vitro, Phoma putaminum isolates were pathogenic to onion cvs. Mercedes and Excalibur, resulting in necrosis of young bulbs and roots seven days after inoculation. Disease incidence caused by P. putaminum was higher in cultivar Mercedes, ranging from 75 to 100%, than in P. macrostoma var. incolorata (0 to 25%). No symptoms were observed on cultivar Excalibur inoculated with P. macrostoma var. incolorata or on control plants. In vitro inoculations of commercial onion bulbs and field inoculations of roots failed to reproduce symptoms, thus showing that P. putaminum and P. macrostoma var. incolorata are weak pathogens. Sequence size of the nuclear internal transcribed spacer (ITS) of ribosomal DNA (rDNA) gene ranged from 458 to 610 base pairs (bp) for P. putaminum and was 456 bp for P. macrostoma var. incolorata isolate. Analysis of rDNA ITS region by PCR-RFLP showed that restriction enzyme, Hindlll, among other restriction enzymes evaluated (Alul, EcoRI, Clal and Seal), differentiate between P. putaminum and P. macrostoma var. incolorata isolates.

Effect of acid deposition on trichome morphology and dogwood anthracnose biology

1992 ◽  
Vol 50 (1) ◽  
pp. 840-841
Author(s):  
Kyle T. Thornham ◽  
R. Jay Stipes ◽  
Randolph L. Grayson
Keyword(s):  
Acid Deposition ◽  
Disease Incidence ◽  
Natural Populations ◽  
Tree Disease ◽  
Flowering Dogwood ◽  
Discula Destructiva ◽  
Disease Induction ◽  
Dogwood Anthracnose ◽  
Trichome Morphology ◽  
Precipitation Events

Dogwood anthracnose, caused by Discula destructiva (1), is another new catastrophic tree disease that has ravaged natural populations of the flowering dogwood (Cornus florida) in the Appalachians over the past 15 years, and the epidemic is prognosticated to continue (2). An estimated 9.5 million acres have been affected, primarily in the Appalachian Mountains, from VA southwards, alone, and an estimated 50% of all dogwoods in PA have been killed. Since acid deposition has been linked experimentally with disease induction, and since the disease incidence and severity are more pronounced at higher elevations where lower pH precipitation events occur, we investigated the effect of acidic foliar sprays on moiphologic changes in the foliar cuticle and trichomes (3), the initial sites of infection and foci of Discula sporulation.

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