J, proper air flow is important, positive air in and positive air out is best, oscillating fans within the foliage also help to stimulate strong stems AND move the air (and the moisture) away from the foliage. Rotating crops is of course moot if its container growing but if in native soil in beds or some such in a greenhouse it would behoove the grower to use judicious amounts of fertilizewr, in whatever form is deemed just. Organic mulch, compost tea, mineral fertilizers etc.
One of the best ways to learn to grow in a contained area is to see a well managed pot grow room, very valuable crop so doing things efficiently is paramount. I have seen rooms with machinery for CO2, ambient temperature, water level, humidity, nutrient levels, nutrient solution temperature management etc, fantastic attention to detail and control.
in regards to grafted seedlings having disease resistance, the only plant I know of that has an effect that way is tomatoes. On the label you may see "V' 'F' 'N' and/or 'T' which are indications of resistance to pests or disease such as: verticillium wilt, nematodes, fusarium wilt and Tobacco mosaic virus (I think).