Alice--did you check the roots to see if you have a root pathogen? Often when you get a general decline like this--a root disease is an option. If the leaves are mottled you could have a virus--tobacco mosaic perhaps. I cannot tell much by your photo--other than the plant looks chlorotic. It could also be just nitrogen deficiency. Jim White, Rutgers University

The picture looks like you have an immobile nutrient deficiency (newer leaves are affected). What kind of fertilization are you giving it (modified Hoagland, Miracle-gro, etc.)? Just on the pictures alone, my guess is iron deficiency.

Thanks very much for your responses, Dr. White and Myles. I've shown my plant to our school's Home and Garden Center and the plants were negative for CMV, TSWV, INSV and TMV. The extension agent suggested that it looked like herbicide damage, but since the plants were in a growth chamber with no exposure to any chemicals other than fertilizer, iron or magnesium deficiency are more likely. I've been feeding the plants once a week with 15-5-15 Ca Mg (Jack's) fertilizer. Perhaps I will try supplementing with more iron? We didn't rule out a root pathogen - what is a good way to check this? Thanks again for your help.

Alice--look for root discoloration--or any evidence of necrosis in the root system. Good luck. Jim White, Rutgers Univerrsity

One other thought at the moment, how close is the plant to the light? There may be some bleaching going on from being too close to your light source.

just check it for Sulfur deficiency. by rapid testing method

Sulfur deficiency in tomato always confused with the nitrogen deficiency many times

I checked the roots and they seem okay. Interesting about the sulfur, thank you Harshal. Myles, that's a good point - I think the plants aren't suffering from being too close to the light, though, because they are several feet under it in my growth chamber, and the symptoms haven't occurred on all my plants.

I had been watering my plants with distilled water mixed with commercial fertilizer, and my advisor pointed out that the fertilizers are formulated to be mixed with tap water, so I'm going to switch to that.

Ok, not the light. The tap water might do it for you. Let us know if they come back afterwards! We always make our fertilizers with the tap water here. We take a water sample of the tap, and then adjust our nutrient solution based on the results (we have high calcium). Good luck!

Ooh, thanks for the info Myles. My lab studies calcium signaling so I should definitely check our water for that.

Alice, have you found the reason of  the problem? We have got similar symptoms in field, and looking for practical solution.

Alex

Hello, Alex, I'm sorry that your tomatoes are also experiencing these symptoms. I never confirmed what the problem was. The symptoms seen on my tomatoes were so non-uniform that I suspected it wasn't a nutrient deficiency, but I switched fertilizer just in case.  I switched growth chambers and stopped having the problem. I suspect that the air intake for the old growth chamber was taking in a harmful compound applied to the lawn outside my building.  

Good luck with your plants! Please let us know how it goes.