I have 2 Sun Gold tomatoes that are developing yellow patches on the leaves. The symptom started on the bottom leaves, and seems to be moving up. The two plants are separated by other types of tomatoes, and none of the other types is showing this problem. Is this a nutrient deficiency or disease ? Will this spread? FYI, I'm pretty new to vegetable gardening, and this is the first year I grow Sun Gold tomatoes. Thank you for your help.