scholarly journals Initial Inoculum and Spatial Dispersal of Colletotrichum gloeosporioides, the Causal Agent of Strawberry Anthracnose Crown Rot

Plant Disease ◽  
2015 ◽  
Vol 99 (1) ◽  
pp. 80-86 ◽  
Author(s):  
Mahfuzur Rahman ◽  
Peter Ojiambo ◽  
Frank Louws
Keyword(s):  
Power Law ◽  
Colletotrichum Gloeosporioides ◽  
Exponential Model ◽  
Crown Rot ◽  
Plant Production ◽  
Inoculum Source ◽  
Initial Inoculum ◽  
Nursery Production ◽  
Mother Plants ◽  
Modified Power Law

Anthracnose crown rot (ACR), caused by Colletotrichum gloeosporioides, is a serious disease of strawberry (Fragaria × ananassa) in nurseries and fruiting fields in the southeastern United States. This study was conducted to determine the potential of alternative hosts for initial inoculum source and spread that causes ACR in strawberry nurseries. Results indicated that Parthenocissus quinquefolia is a noncultivated host of C. gloeosporioides in North Carolina and may serve as an initial inoculum source for planting material. Sources of inoculum data were complemented with a 2-year study of disease incidence and spread in simulated nursery production experiments. Sixty days after inoculation of the mother plants in the nursery, three different inoculation levels showed a significant positive correlation (r = 0.78, P < 0.004) with the quiescent infection (QI) incidence on the runner or daughter plants at the end of the nursery production cycle. Runner plant counts from different proportion of mother plants' inoculation treatments indicated that runner plant production was negatively and significantly (P < 0.001) affected by C. gloeosporioides. Infected tips used to produce transplants destined for fruit production resulted in 29.3 and 16.8% mortality in plug trays in 2007 and 2008, respectively. Tracking foliar QI incidence that resulted from dispersal of inoculum from an introduced point source in the nursery showed a sharp decline at 1 m and beyond from the inoculation focus. Although the exponential model (R2 = 0.92 to 0.94) had slightly higher coefficients of determination than the modified power law (R2 = 0.89 to 0.90), residual plots indicated that the modified power law model fit the disease gradient data better than the exponential model in both years. Results from our dispersal study indicated that rogueing of infected plants within a 4-m radius of infection foci would reduce the risk of transferring infected runner plants from the nursery to the fruiting field.

Primary Disease Gradients of Wheat Stripe Rust in Large Field Plots

2005 ◽  
Vol 95 (9) ◽  
pp. 983-991 ◽  
Author(s):  
Kathryn E. Sackett ◽  
Christopher C. Mundt
Keyword(s):  
Stripe Rust ◽  
Power Law ◽  
Puccinia Striiformis ◽  
Exponential Model ◽  
Plant Diseases ◽  
Large Field ◽  
Data Sets ◽  
Wheat Stripe Rust ◽  
Primary Disease ◽  
Modified Power Law

Field data on disease gradients are essential for understanding the spread of plant diseases. In particular, dispersal far from an inoculum source can drive the behavior of an expanding focal epidemic. In this study, primary disease gradients of wheat stripe rust, caused by the aerially dispersed fungal pathogen Puccinia striiformis, were measured in Madras and Hermiston, OR, in the spring of 2002 and 2003. Plots were 6.1 m wide by 128 to 171 m long, and inoculated with urediniospores in an area of 1.52 by 1.52 m. Gradients were measured as far as 79.2 m downwind and 12.2 m upwind of the focus. Four gradient models—the power law, the modified power law, the exponential model, and the Lambert's general model—were fit to the data. Five of eight gradients were better fit by the power law, modified power law, and Lambert model than by the exponential, revealing the non-exponentially bound nature of the gradient tails. The other three data sets, which comprised fewer data points, were fit equally well by all the models. By truncating the largest data sets (maximum distances 79.2, 48.8, and 30.5 m) to within 30.5, 18.3, and 6.1 m of the focus, it was shown how the relative suitability of dispersal models can be obscured when data are available only at a short distance from the focus. The truncated data sets were also used to examine the danger associated with extrapolating gradients to distances beyond available data. The power law and modified power law predicted dispersal at large distances well relative to the Lambert and exponential models, which consistently and sometimes severely underestimated dispersal at large distances.

scholarly journals The Effects of Dispersal Gradient and Pathogen Life Cycle Components on Epidemic Velocity in Computer Simulations

2005 ◽  
Vol 95 (9) ◽  
pp. 992-1000 ◽  
Author(s):  
Kathryn E. Sackett ◽  
Christopher C. Mundt
Keyword(s):  
Life Cycle ◽  
Stripe Rust ◽  
Power Law ◽  
Field Data ◽  
Exponential Model ◽  
Infectious Period ◽  
Multiplication Rate ◽  
Dispersive Wave ◽  
Modified Power Law ◽  
Over Time

The velocity of expansion of focal epidemics was studied using an updated version of the simulation model EPIMUL, with model parameters relevant to wheat stripe rust. The modified power law, the exponential model, and Lambert's general model were fit to primary disease gradient data from an artificially initiated field epidemic of stripe rust and employed to describe dispersal in simulations. The exponential model, which fit the field data poorly (R 2 = 0.728 to 0.776), yielded an epidemic that expanded as a traveling wave (i.e., at a constant velocity), after an initial buildup period. Both the modified power law and the Lambert model fit the field data well (R2 = 0.962 to 0.988) and resulted in dispersive epidemic waves (velocities increased over time for the entire course of the epidemic). The field epidemic also expanded as a dispersive wave. Using parameters based on the field epidemic and modified power law dispersal as a baseline, life cycle components of the pathogen (lesion growth rate, latent period, infectious period, and multiplication rate) and dispersal gradient steepness were varied within biologically reasonable ranges for this disease to test their effect on dispersive wave epidemics. All components but the infectious period had a strong influence on epidemic velocity, but none changed the general pattern of velocity increasing over time.

scholarly journals Epidemiological Significance of Crown Rot in the Fruiting Field in Relation to Colletotrichum gloeosporioides Infection of Strawberry Nursery Plants

Plant Disease ◽  
2017 ◽  
Vol 101 (6) ◽  
pp. 907-915
Author(s):  
Mahfuzur Rahman ◽  
Frank J. Louws
Keyword(s):  
North Carolina ◽  
Colletotrichum Gloeosporioides ◽  
Disease Risk ◽  
Crown Rot ◽  
Research Station ◽  
Yield Losses ◽  
Marketable Yield ◽  
Percent Increase ◽  
Mother Plants ◽  
Fruit Harvest

Anthracnose crown rot (ACR), caused by Colletotrichum gloeosporioides, is a serious disease of strawberry (Fragaria × ananassa) in the southeastern United States, and there is a need to determine the link between nursery and fruiting-field disease risk. A 2-year study in 2007, repeated in 2008, was conducted at the North Carolina State University Horticultural Crops Research Station, Clinton, using ‘Chandler’, the most popular cultivar in North Carolina and one that is highly susceptible to ACR. Mother plants in a summer nursery were inoculated midseason with three pathogenic strains of C. gloeosporioides at an incidence level of 0, 5, 10, or 25%. Asymptomatic runner plants were selected at maturity (85 to 88 days after inoculation) from the nursery in early to mid-October from within a 0.5-m (inner) or 0.5- to 1.0-m (outer) radius around inoculated mother plants and planted into a plasticulture fruiting field system, with fruit harvest in April to June the following spring. Plants collected from the 25%-inner treatment had the greatest area under the disease progress curve (AUDPC) values, with a terminal ACR-related plant mortality of 32 and 20% by the end of fruit harvest and marketable yield losses of 30.5 and 30.2% in 2007–08 (Yr1) and 2008–09 (Yr2) seasons, respectively. All treatments increased AUDPC values compared with noninoculated treatments except the 10%-outer (O) and 5%-O treatments in Yr1 and Yr2, respectively. Marketable yield decreased 291.6 kg/ha for every percent increase in inoculum level (i.e., 0 to 25%, R2 = 0.696, P = 0.001). Levels of quiescent infection (QI) incidence (percentage of sampled leaves) assessed 25 to 28 days before digging runner plants also directly affected yield. For example, yield decreased 131.0 kg/ha for every percent increase in QI incidence in mother plants (R2 = 0.744, P = 0.001). Immersion of plants in fungicide solutions prior to planting decreased AUDPC values and improved plant stand by 7 to 11% but did not affect marketable yield compared with controls. This study provides results that can enable nursery and fruit growers to assess risk and implement mitigation measures to limit nursery plant and fruit yield losses.

A novel formulation for blood trauma prediction by a modified power-law mathematical model

2005 ◽  
Vol 4 (4) ◽  
pp. 249-260 ◽  
Author(s):  
Mauro Grigioni ◽  
Umberto Morbiducci ◽  
Giuseppe D’Avenio ◽  
Giacomo Di Benedetto ◽  
Costantino Del Gaudio
Keyword(s):  
Mathematical Model ◽  
Power Law ◽  
Modified Power Law ◽  
Blood Trauma

scholarly journals Constraints on the distribution of supernova remnants with Galactocentric radius

2015 ◽  
Vol 454 (2) ◽  
pp. 1517-1524 ◽  
Author(s):  
D A Green
Keyword(s):  
Cosmic Rays ◽  
Power Law ◽  
Supernova Remnants ◽  
Exponential Model ◽  
Galactic Centre ◽  
Selection Effects ◽  
The Galaxy ◽  
Best Fitting ◽  
Galactic Longitude ◽  
Galactic Distribution

Abstract Supernova remnants (SNRs) in the Galaxy are an important source of energy injection into the interstellar medium, and also of cosmic rays. Currently there are 294 known SNRs in the Galaxy, and their distribution with Galactocentric radius is of interest for various studies. Here I discuss some of the statistics of Galactic SNRs, including the observational selection effects that apply, and difficulties in obtaining distances for individual remnants from the ‘$\Sigma$–D’ relation. Comparison of the observed Galactic longitude distribution of a sample of bright Galactic SNRs – which are not strongly affected by selection effects – with those expected from models is used to constrain the Galactic distribution of SNRs. The best-fitting power-law/exponential model is more concentrated towards the Galactic Centre than the widely used distribution obtained by Case & Bhattacharya.

Thermo-Mechanical Vibration Analysis of Imperfect Inhomogeneous Beams Based on a Four-Variable Refined Shear Deformation Beam Theory Considering Neutral Surface Position

2019 ◽  
Vol 24 (3) ◽  
pp. 426-439
Author(s):  
Farzad Ebrahimi ◽  
Ali Jafari
Keyword(s):  
Mechanical Properties ◽  
Shear Deformation ◽  
Power Law ◽  
Volume Fraction ◽  
Beam Theory ◽  
Refined Theory ◽  
Neutral Surface ◽  
Thickness Direction ◽  
Neutral Surface Position ◽  
Modified Power Law

In this disquisition, an exact solution method is developed for analyzing the vibration characteristics of porous functionally graded (FG) beams by considering neutral surface position and different thermal loadings via a four-variable shear deformation refined beam theory. Four types of environmental conditions through the z-axis direction are supposed as: uniform (UTR), linear (LTR), nonlinear (NLTR) and sinusoidal (STR) temperature rises. Mechanical properties of porous FG beams are supposed to vary through the thickness direction and are modeled via the modified power-law. The modified power-law is formulated using the concept of even and uneven porosity distributions. Since the variation of pores along the thickness direction influences the mechanical properties, porosity plays a key role in the mechanical response of FG structures. The governing differential equations and related boundary conditions of porous FG beams are subjected to temperature field that is derived by Hamilton's principle based on a four-variable refined theory which verifies shear deformation regardless of any shear correction factor. The Navier-type solution procedure is used to achieve the natural frequencies of porous-FG beams supposed to various thermal loadings which satisfies the simply-simply boundary condition. A parametric study is led to carry out the effects of material graduation exponent, porosity volume fraction, different porosity distribution, and thermal effect on dimensionless frequencies of porous FG beams. It is concluded that these parameters play noticeable roles in the vibration behavior of imperfect FG beams. Presented numerical results can be applied as benchmarks for future designs of imperfect FG structures with porosity phases.

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