2/9/2015. Dispersal. Light. Chemical. Spatial and temporal scales of atmospheric motion systems are cross dependent.

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1 Dispersal Light Nicholas Dufault Epidemiology Lecture February 8, 2015 Chemical That atmosphere extends 700 km above the earth. We focus on less than 0.05% for biota. Spatial and temporal scales of atmospheric motion systems are cross dependent. Biota flow in the atmosphere is known to occur at different stages. Biota boundary layer thickness can vary during different atmospheric conditions. 1

2 The structure of the surface and planetary boundary layers vary between night and day. Daytime Warm air 1 to 3 km Nighttime Cool air 0.3 to 0.5 km Surface layer 1 to 2 times the canopy top Wind profiles change with adjustments in surface roughness elements (i.e. plants). The size of eddies and horizontal distance traveled increases with height. Spores must cross the laminar layer in order to enter the turbulent layer for transport. Fungal spores can be liberated through a variety of different mechanisms. A. Gusts & heating B. Evaporation Passively liberated spores Dependent on environment (peak daytime) Puccinia, Uromyces, Ustilago, Blumaria, Bipolaris Actively liberated Independent of environment (peak night) Pyricularia oryzae, Cronartium, Peronospora C. Osmotically rupturing D. Drying and twirling E. Gravity 2

3 Spore liberation/take off can be assisted by raindrops. Spore concentrations decrease rapidly with height and distance from the source. A. Direct dispersal B. Indirect dispersal Height C. Splash dispersal Source Downwind Distance D.E. Aylor As an epidemic progresses, so does the number of spores that can be transported. Mundt et. al., 2009 EcoHealth 6, Eq. [7.33] of Madden et al., 2007 Relatively significant spore deposition near the source with wind and gravity. Sedimentation Gravitation settling Laminar layer (mm to meters) Impaction Wind assisted deposition High wind speeds Rainfall can deposit large quantities of spores at long distances from the source. Rainfall Washout Provides moisture for infection Removes a column of spores 3

4 Canopy structure can impact the deposition of spores at different depths. Environment after initial deposition can effect where the spores finally end up. Dufault et. al (2): Insects can be passively &actively transported in the atmosphere. Bimodal flight related to avoidance of strong winds and rain. The Influence of Light Some insects fly with frontal weather systems. Electromagnetic Radiation (EMR) A large portion of the EMR is absorbed by the atmosphere. In the atmosphere the Ozone absorbs UV light. 4

5 What effects do you think light can have on fungal spore? UV light has varying effects on all biological organisms. No response: light has no effect on fungal development properties. Stimulates: light can increase the developmental stage of the fungus. Inhibits: light can reduce the development or kill the fungus. EMR effects cannot be completely separated from other environmental factors. UV B can affect both pathogens & insect pests. DNA damage Modify gene expression Nordskog, B. et al Phytopath. 97: Increased UV B has an effect on the host. Light can inhibit fungal sporulation. Change metabolites Leaf anatomy Cuticle thickness Leaf thickness Some metabolites (i.e. flavonoids and carotenoids) are associated with fungal resistance. Lettuce downy mildew (Bremia lactucae) Waveband ranges 400 to 450 nm 450 to 500 nm 500 to 500 nm Nordskog, B. et al Phytopath. 97:

6 Other wavelengths besides UV can modify sporulation. UV light can be required for sporulation of fungal pathogens. Cucumber Downy Mildew PE Type Description 1 No UV B absorbance 2 PE1 + blue pigment 3 85% UV B absorbance 4 PE 3 + blue pigment 5 100% UV B absorbance 6 PE5 + blue pigment Note: blue pigment absorbs part of spectrum (peak 580 nm) The role of other light wavelengths associated with UV light needs to be assessed. Reuveni, R. et al Plant Dis. 81: Raviv, M. and Antignus, Y. UV radiation effects on pathogens and insect pests of greenhouse grown crops. Spores can be damaged/killed by varying intensities of light. Pathogen Spore Type Critical Dose (MJ m -2 )* P. infestans sporangia 0.9 P. tabacina sporangia 2.4 V. inaequalis conidia 21 P. pachyrhizi urediniospore 21 U. appendiculatus urediniospore 25 A. solani conidia 35 *The critical dose results in 63.2% mortality for the exposed spore population. Spore death from light (UV) critical to long distance transport. Case Study: Soybean Rust Transport 1,300 km, 100 h Greater UV intensity higher in atmosphere Spores exposed to solar irradiances of Cloudy 12.5 MJ/m 2 Clear 50 MJ/m 2 62% and 0% of the urediniospores survive Aylor, D.E Agri & Forest Meteo. 97: Isard, S. A. et. al Plant Disease. 90: Isard, S. A. et. al Plant Disease. 90: Light may stimulate or inhibit spore germination. Light intensity influences penetration and infection. Direct effects pathogen Susceptibility of host Isard, S. A. et. al Plant Disease. 90: Wu, B. M. et al Phytopath. 90: Septoria tritici Puccinia striiformis Exposure to blue or red to far red wavelengths can stimulate oospores of Phytophthora species. Ribeiro, O. K., et al. Mycologia. 68, No Benedict, W. G Physiol. Pl. Path. 1:55 66 de Vallavieille Pope et al Phytopath. 92:

7 Insects are affected by UV light reductions in the greenhouse. The Influence Chemicals Insect compound eyes are adapted to sense UV wavelengths. Thus, light affects insect orientation and navigation. Kumar, P. et al Environ. Entomol. 35: Pathogens can be affected by chemicals in the atmosphere and soil. Soil ph extremes can affect disease development. Air pollutants Soil ph Fertilizer Herbicide Potato scab Severe in neutral Isolates ph < 5.0 Cotton root rot Common alkaline soil Limited in acidic Club root of cabbage Inhibited by neutral Inhibited by alkaline Fertilizers influence disease develop by altering soil environment and plant growth. Herbicides can enhance and inhibit disease development. Enhance High incidence of damping off in sugar beets Chlorimuron (Classic) higher incidence of TSWV Inhibit Glyphosphate with rust fungi Trifluralin reduced root rot of pea (Aphanomyces euteiches) 7

8 Pollutants can affect both the host and the pathogen. Ozone effects on host Fungi from barley grain Ozone effects on fungi Allen, B. et al J. Environ. Sci. and Health. B38: