With no further info (variety, age since transplant) and no image of the entire plant, it is difficult to guess. Assuming the plant's appearance shows symmetrical loss of chlorophyll, then a strong possibility is a nutrient deficiency or excess, either of which could be the result of an unsuitable soil pH. [Mg deficiency, "nutrient excess or deficiency", potassium deficiency, sulfur deficiency.] They all can look the same.
Scan through the deficiencies on IPM Images:
https://www.ipmimages.org/browse/AreaSubs.cfm?area=62. Clicking on an individual image will take you to the detail page. The image can then be displayed full screen. Some entries contain more info than others.
If only one side of the plant is affected, or one side of certain leaves, then you might consider Fusarium wilt:
https://www.ipmimages.org/browse/detail.cfm?imgnum=5424464
A soil analysis would be helpful, as well as a fertilizer history.
Bob