Narimene, have you included potato as control for inoculation success?

No , I didn't

Thank you for the idea

First, What do you mean by positive control? Or what kind of positive control did you use? The real positive control should be a same potato variety from which Alternaria solani pathogen was isolated. But in any case, I think yes, it is possible to get no necrosis on positive control, and you can find explanation for that on disease triangle concepts (host-pathogen-environment). For example, It could be that the concentration of Alternaria solani from your inoculum was not high enough to successfully induce the disease.... etc.

Dear Joao ,

A positive control means that the leaf ( tomato) was inoculated only bu fungi, without treatment ( fungicide).

It should be the same variety , but the purpose of my study is to see if this fungi (A.solani) has developed any immunity or sensivity to some fungicides such as Chlorothalonil , azoxystrobine+difenoconazole,difenoconazole., using others varieties.

Yes we may obtain no necrosis , but the thing is that I have obtained some necrosis on leafs that I have treated with fungicide

How do you explain that ?

Ps: I took the inoculum from the same petri dish

How did you inoculate it? How many replications per treatment? Are all plants/replicates from positive control showing no necrosis?

1. I have inoculated with " explantin" 

• 3 repetitions/ treatmet ( for fungicide) 
• 2 repetitions for positive control 
• 3 repetitions for natural control ( only the leaf ) 

2. no only those which have been inoculated with A.solani ( isolated from potato) 

What do you mean by explantin?

Sorry , fungal explant