Spread of Plant Disease on a Continental Scale: Role of Aerial Dispersal of Pathogens

Abstract

Successful transmission of plant diseases over long distances through the atmosphere depends on the reproductive rate of the pathogens, on the carrying capacity of the source locality, on atmospheric turbulence, stability, and wind speed, and on the survival of spores during exposure to inhospitable temperature and humidity and to UVB radiation from the sun. These interacting factors were incorporated into a model to estimate the rate and extent of seasonal incursions of disease from southern into northern areas of the United States. The model indicates a practical limit for long-distance dispersal (LDD) of a plant pathogen, which depends strongly on its fecundity and on its ability to survive in the atmosphere. Two classic plant diseases, stem rust of wheat and tobacco blue mold, are used to illustrate the model. Both diseases appear to spread northward on average at about the same rate as the seasonal advance of the ''green wave'' of available susceptible host tissue. The near concordance of the disease wave and the green wave underscores two important points. First, it suggests that disease spread over long distances may be limited more often by pathogen establishment than by LDD. The green wave also reduces the stochastic variability and speed of disease spread by presenting a barrier to potential long-distance, lowprobability dispersal events. Second, it helps to focus attention on alternative pathways for disease spread and on possible unappreciated niches for overseasoning, both of which can have important implications for disease control strategies.

Effects of Host Variability on the Spread of Invasive Forest Diseases

“…Strong filtering exists between the different phases; successful invasion is a rare event such that only a small fraction of alien species survive to pass through and establish themselves in a novel environment. Both host availability (as a suitable ecological niche) and environmental conditions (extremes of temperature, moisture, and UV radiation) in the new location place strong limitations on a pathogen's survival, its ability to reproduce and disperse, and subsequently spread [19,20]. These factors act as a strong selection filter leading to rapid adaptation to new environmental conditions and rapid evolution and exploitation of novel hosts [20].…”

“…Understanding novel forest pathogen introductions and the factors driving invasion success requires a deeper understanding of the invasion sequence that is conditioned by local or long-distance transport mechanisms from their native habitat to a novel environment, as well as environmental conditions and ecological factors determining an organism's survival and reproducibility, and any population and community effects affecting their dynamics across a range of spatial and temporal scales (see Figure 1). (extremes of temperature, moisture, and UV radiation) in the new location place strong limitations on a pathogen's survival, its ability to reproduce and disperse, and subsequently spread [19,20]. These factors act as a strong selection filter leading to rapid adaptation to new environmental conditions and rapid evolution and exploitation of novel hosts [20].…”

The Population Genetic Structure of Clonal Organisms Generated by Exponentially Bounded and Fat-Tailed Dispersal

“…Fungal spores causing severe agricultural diseases are dispersed in rare events over hundreds or even thousands of kilometers . Transport through the air is profoundly affected by turbulence over a wide range of spatial scales (Aylor 2003;Nathan et al 2005).…”

“…A recent study addressing the above problems showed that dispersal of the wheat stripe or yellow rust fungus (Puccinia striiformis) fitted a power-law model well if enough sufficiently distant spore traps were used (Sackett and Mundt 2005). Moreover, although several physical processes underlie wind dispersal, theoretical arguments strongly propose that LDD of small objects can be modeled by a single function that will have inverse power-law behavior in the tails (Shaw 1995;Kot et al 1996;Stockmarr 2002;Aylor 2003;Shaw et al 2006). Uplift is the most important factor for heavier propagules but many factors are equally important for smaller objects such as spores (Nathan et al 2005).…”

Patchy patterns due to group dispersal

“…The models we had in mind are based on spatial point processes as in Section 4.4 and in Austerlitz et al (2004), Klein et al (2006a), Minogue (1989) and Tufto et al (1997). There also exist models including LDD which are based on Gaussian puff or differential equations (Aylor, 1987(Aylor, , 2003Ferrandino, 1993). In these models, which take the vertical dimension into account, the turbulence allows the particles to escape the canopy and to be transported over long distances.…”