Is there a way to analyse any possible inhibition effects of one pathogen on the other or possibly any other interactions between them ? e.g. one pathogen might just weaken the plant defenses without causing any symptoms, therefore facilitating easiest infection of the symptom-causing pathogen...
You might want to find the interactions between the pathogens first just cocultivating them in plates. Then, you can use systems like the gnotobiotic system to grow plants in sterile conditions and infect them with both pathogens. In this case you should use single-pathogen infected plants and healthy plants as controls. But if I was you I might specify better my hypothesis about what might happen to better design your experiment. Doses might play an important role too, as well and infection time and plant phenology. Too many things to be answered by the readers without more information...
Best wishes.
Thank you for your answer. What I am actually trying to investigate is early blight of potatoes. The literature is quite inadequate in identifying whether the disease is purely caused by A. solani or it is mixture of more than one Alternaria species. So far most of my isolation work is showing that in early blight lesion A. solani and A. alternata are both present, so I am looking of a way to find out whether the presence of A. alternata is of any importance to the early blight disease or it's just an opportunistic pathogen or even just a non-host present pathogen
Then I think single species inoculation and a treatment with both together might help you. At least as a first approach to see if there are any synergistic effects...
I've done this already in-vitro. Seemed to be a small difference in one of the cultures when grown together but this doesn't prove there is any inhibition other than some competition for resources maybe. And if done in plants what would you think it an appropriate measurement protocol ? Just extend and growth rate of lesions ? I was thinking there might be a more in-depth technique, maybe some kind of molecular technique to prove there is any interactions but all I can think so far are traditional microscopy and infection parameter methods (lesion growth, rate of growth, number of lesions, etc...)
You can see the expression pattern of genes spatially defense genes and developmental genes related to phytohormone production by using RTPCR. Such type of study with basic study will confirm the interaction pattern. You can also monitor the physiological changes in the plant by biochemical studies after pathogen inoculation i. e. level of antioxidants, level of reactive oxygen species and some enzymatic assay.
Thank you for your answer. Do you have any specific phytohormone genes in mind ?
EIN for ethylene signaling, PDF1.2 for Jasmonate signaling, you can easily get the list on Google and many research articles also.
Growing these two pathogens in-vitro may not show much of a difference. As with pathogens, the extent of pathogenecity alone or in combination with another pathogen is best expressed when they infect plants i.e. in the presence of a defense system. However, as A. solani and alternata are two relatively same pathogens and probably they would add each other in infection.
Ioannis, Alternaria alternata is very complex species that include pathogenic and non-pathogenic strains. Any Alternaria can easy turn to saprophyte after several sub-culturing on artificial medium. I guess the Alternaria alternata population virulence is changing during the summer season from very low to high level in correlation to amount of plants available for initial infection. Some ideas can be found at work "Linking emergence of fungal plant diseases and ecological speciation" http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2885483/
look for initial infection. then grow under in-vitro conditions. You may find aa mostly growing as saprophyte. But its very easy to identify between two.
Ioannis, I agree with Alex. As you know, today we cannot talk about species, but complex species. Besides differences in virulence among the species which can infect potatoes, such as Alternaria alternata, A. grandis, and A. solani, we can find considerable differences among isolates of these species. Therefore, I suggest you choose a specific interaction to elucidade the infection process. Leaf age and nitrogen fertilization play an important role in disease establishment and evolution and might be considered, especially for a weak pathogen like A. alternata.
Alex thank you for your answer. Do you have any references for alternaria species turning saprophytic after culturing ?