Dear all
I hope you have a good tima.
would you please help me. This looks like Alternaria?
Possibly Early Blight caused by Alternaria solani? See images here:
https://www.google.ca/search?q=images:+early+blight+tomato&biw=1920&bih=876&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjP5O3A1rLOAhVr6IMKHQ6ZBpkQsAQIGg
Symptoms of early blight occur on fruit, stem and foliage of tomatoes and stem, foliage and tubers of potatoes. Initial symptoms on leaves appear as small 1-2 mm black or brown lesions and under conducive environmental conditions the lesions will enlarge and are often surrounded by a yellow halo. Lesions greater than 10 mm in diameter often have dark pigmented concentric rings. This so-called “bullseye” type lesion is highly characteristic of early blight.
Please see: https://pubs.ext.vt.edu/450/450-708/450-708_pdf.pdf
These symptoms are characteristic and definitely caused by Alternaria solani
There is no “bullseye” type lesion which is highly characteristic of early blight. Use the microscope and look for characteristic spores of Alternaria sp. Symptoms are reminiscent of pesticide phytotoxicity or nutrient deficiency.
I fully agree with Franci. Do not buy it as early blight, caused by Alternaria sp. Microscopic examination after leaving leaf samples in a moist chamber for 48 hours should indicate the presence of Alternaria, that must be checked for pathogenicity after isolation, before confirming the diagnosis. However, I would consider a strong possibility of nutrient deficiency or pesticide toxicity, or a virus infection. Informations on distribution of diseased plantas in the field an cultural practices adopted in the crop need to be obtained for completing the diagnosis
leaf mosaic, yellow and curly young leaves, non-fertilized flowers: it looks like virus symptons. Regards.
Dear Franci and Carlos, I am impressed you do not see the characteristic, target-like lesions on the leaves surrounded by chlorotic halo shown on the first picture...It happens I have worked with both the pathogen and the host in few projects, thus I know exactly how they look like. Please do not confuse people with answers like, probably this or that, either virus, toxicities, deficiencies bacteria, fungi or whatever.....!
Dear Elaheh, the best way to find out is by isolating the pathogen from the infected tissue. Follow the instructions provided by Carlos, although, you could see the characteristic conidia forming a chain (one on top of the other) on conidiophores, under a stereoscope. And then please let us know what you found...! Thanks...
Dear Anastasios,
if you see target-like lesions on the first picture, I do not. And what do you say about chlorotic leaves without lesions. On the third picture are very uncharacteristic symptoms for the Alternaria sp. I also proposed Elaheh a microscopic examination. In the attachment, you can find my photos of symptoms characteristic for the Alternaria sp. on tomato leaves and stem (target-like lesions).
Best regards, Franci
Nice discussion. I don´t think symptoms are related to Alternaria; I´m attaching a technical paper with two pictures of Alternaria lessions in tomato (pp. 39 y 40). Usually is easy to catch Alternaria conidia from lessions just grasping on it with a piece of tape, putting a drop of metilen blue on a glass plate and taking a look on microscope. Typical conidia, if present, will easily be seen (last picture of Franci or p. 40 in the attachment). Tell us what you find, please. Best regards.
Dear Franci,
Thanks for this. These, of course, are characteristic symptoms of Alternaria infection. Although, disease symptoms in the field may differ to those due to different pathogen races, host defence defence responses etc. It is rather clear that most symptoms shown in picture 2 and 3 do not match those shown in picture 1 and probably are of other nature (i.e. nutrient deficiencies or toxicity, bad watering etc.). However, when it comes to infected plants, we may focus on the pathogen that cause the higher crop losses, even if we can see or isolate more than one on different or same infection sites. Care has to be taken for the initial and most aggressive one. Alternaria, although a secondary and sometimes saprophytic fungus, it can devastate tomato plant and cause severe crop losses. So, when it comes to decide for field application I would recommend chemical control for Alteraria, rather than dealing with deficiency or toxicity problems (which in that stage is not possible).
Other than that, I completely agree with the laboratory examinations proposed by the former scientists.
Elaheh, can you give some more details about tomato cultivation conditions? So far:
1) it does not look like early blight
2) you need to look at spores (if any are present) as it was suggested before, and test plants for viruses.
3) it can be toxic effect as Oadi suggested.
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