Tomato plants have clear chlorosis on young leaves and necrotic lesions at the eges of affected leaves. Is it physiological disorder, frenching disease, or virus infection?
The quality of the photos is rather low, but I notice neither black dots, mosaic patterns nor accentuated leaf-rolls.
Knowing the environmental conditions, the insect population and the applied chemicals would be really helpful.
Unless you notice a rosette appearance, I would say physiological disorder caused by either herbicides or nutrients.
The symptoms can be caused by deficiency of magnesium or manganese or micronutrients.
Tomato plants are highly sensitive to growth regulator herbicides (i.e. phenoxy herbicides) throughout the growing season.
Herbicide damage causes downward curling and narrowing of leaves (string-shape) and chlorosis of the veins. The young leaves do not fully expand and are narrow and elongated. Stems are split, distorted, or brittle.
Frenching (or polyphylla) induces curling and interveinal chlorosis and lead to cessation of terminal bud and stem growth. After apical dominance is lost, a large number of axillary buds develop a slender shape (string- or sword-like) because of the leaf blades failed development. Such plants have the appearance of a rosette.
The current hypothesis regarding the cause is a toxin produced by Bacillus cereus, but similar symptoms are observed under exposure to toxic concentrations of thallium, manganese and lead.
It is frequently observed on particularly wet, poorly ventilated and rather warm soils, of neutral to alkaline pH and which sometimes are inadequately fertilised, lacking available nitrogen.
Tomato Yellow Leaf Curl Virus (TYLCV) would induce upward curling of leaves, chlorotic leaf margins, smaller leaves and plant stunting.
It is transmitted by whiteflies.
The other main viruses affecting tomato do not fit the observable symptoms:
Tomato spotted wilt virus (TSWV) would induce stunted plants and a purplish discoloration on the leaves tip. It is transmitted by thrips.
Tobacco mosaic virus (TMV) would cause mottling of older leaves and narrowing of leaflets. It is transmitted by aphids and grasshoppers.
Curly top virus would induce upper leaflets rolling and develop a purplish color, especially along the veins.
Leaves and stems become stiff. It is transmitted by aphids and grasshoppers.
Cucumber mosaic virus would cause tomato plants to yellow and become bushy and stunted. Leaves may be mottled.
It is difficult to distinguish it from herbicide damages without previous knowledge of applied chemicals or analysis. It is seed-borne, carried by aphids or by other mechanical agents..
Hi,
do you have a control plant which we might compare to? If the experiment is in full soil I would strongly suggest you to use an simple insect net around your control and you might exclude viral infection without further test.
Does this yellowing appear only on one plant or multiple? If multiple plants are showing this discoloration you might think about viral cause but otherwise I would suggest some nutrient related problem since the yellowing appear to be on the upper part of the plant and since potassium is commonly used for tomato I suspect that a deficiency/eccess of it might be the cause of your concern.
However I would still suggest you to test the yellow part for viral symptoms (PCR) and be sure that your environment is free from unwanted viruses.
Please let us know about the results!
Best regards
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