Perhaps an iron deficiency. HS-797/CH142: A Guide to Citrus Nutritional Deficiency and Toxicity Identification
no, it doesn't look like iron deficiency. Could this be tristeza? grows with a dozen other sweet oranges in one pot, this spotting of leaves and stems is observed only in increments of two copies. Photo 1. leaf on the left - a diseased increase. leaf on the right is from the previous increment. Photo 2 from internet.Symptoms due to tristeza virus, viewed on the underside of a leaf of sweet orange by reflected light. Symptoms are the dark green to black broken lines in the leaf veins. These are the same areas that show up as translucent when viewed from the underside of the leaf in transmitted direct sunlight
