Interesting question whose answer is complex because there are so many factors (both biotic and abiotic) involved.
Our work has shown that cover crops can enhance the soil and field environment to favor beneficial insects (“Managing Pests with Cover Crops” in book “Managing Cover Crop Profitably”). Under natural ecosystems or under agricultural systems managed to increase biological diversity (e.g., by using cover crops), there is increased number of organisms that compete with pathogens and insect vectors.
We have found (unpublished data) that tomato grown on cover crop residue had reduced incidences of Tomato spotted wilt (viral disease transmitted by thrips) compared to tomato grown in bare soil.
@Ivan, I believe that we can find all possible types of interaction between cultivated plants, vectors, and pathogens (add wild/weedy plants and environment to this list). Most of pests are vectors for some pathogens (even if they are not well-studied yet). Pests prefer healthy plants, sure, to have more good food, but can be often attracted by chemical signals of some pathogens (Pectobacteria do it for an example). Pathogens often attack plants diseased by other pathogen (many examples for viruses and bacteria). But, natural ecosystems are more robust to epidemic type of pathogen spreading comparing to artificial. Just consider an example of hydroponic glasshouse as "perfect" managed ecosystem.
I think it depends on the type of pathogens you're considering. For fungi, spores are the main form of infection, but they are totally non-mobile. Spores are transported by abiotic vectors like rain and wind. In other cases, like the "Flavescence dorée", a phytoplasma is transported by an insect (Scaphoideus titanus) , and contaminates grapevine plants. The phytoplasma can multiplicate in the plant and in the insect. The pathology spreads at the same rate as the insect movements. For sure, a great surface of the same culture promotes a better level of infection. But, if you breaks the monotony of the field, like with natural hedges, you break the movements of the insect. And you also promote housing for birds, which can predate the insect.
For sure, the question of pathology spreding across the biotope is complex, and needs a multidisciplinary approach.
First of all, thank you all so much for your valued feedback and suggestions on the proposed subject. I agree that this is indeed a very complex and interesting question to be asked.
From a plant perspective, plants specify responses to individual attackers by varying the composition and timing of hormones produced (i.e., salicylic acid [SA] stimulates compounds targeting pathogens and jasmonic acid [JA] tends to produce compounds targeting insects) and further, in some plants, the production of one (SA or JA) inhibits production of the other as shown by Thaler et al. (2010). Also a more recent preliminary work by Chisholm et al. (2014) showed that Pea enation Mosaic Virus indirectly promotes aphid (Acyrthosiphon pisum; vectors) fitness by suppressing plant defenses and that Pea leaf weevil (Sitona lineatus; non vector generlists) indirectly benefits aphid (Acyrthosiphon pisum; vectors) behavior by increasing plant palatability.
And these fairly complex answers (studies) address just one aspect of these by far more complex interactions in managed systems.
Looking at the effects of soil environment in managed systems adds another dimension to it. Thanks for sharing your research Juan!
As Alex mentioned, what about natural ecosystems which are by far more robust and more complex?
For sure, I agree that the question of pathology of a specific type of pathogen spreading across the biotope is complex, and needs a multidisciplinary approach. Thanks Bertrand!
Thaler, J.S., Agrawal, A.A. and Halitschke, R., 2010. Salicylate‐mediated interactions between pathogens and herbivores. Ecology, 91(4), pp.1075-1082.
Chisholm, P., Eigenbrode, S.D., Crowder, D. 2014. Can non-vector herbivores suppress the spread of a plant virus? Annual Meeting Entomological Society of America, Nov. 20
Yes...I think spread of soil borne pathogen is also an interesting idea. It involves pathogens like bacteria , fungi and plant parasitic nematodes. These have their infectious spores, mycelia, sclerotia and eggs & larvae. They compete with natural microflora in rhizosphere and get entry inside the host when the balance is shifted towards them. Nematodes make entry generally through stylet making holes which facilitate the entry of secondary I
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