fungal and bacterial diseases, which multiply in wet weather,
especially if the temperatures are high. Many of these selections come from the work of public-domain plant-breeding programs at universities in the Southeast, where disease has long been an issue. Now gardeners in the rest of the country are facing more tomato diseases, due to changing weather patterns, the shipment of bedding and garden plants over long distances, and the inexorable spread of pathogens over time.
There are few open-pollinated varieties with absolute resistance to specific strains of disease, which has been bred into some modern hybrids. On the other hand, some of the o-p varieties have been selected both for resistance to specific types of disease and for general good health--a "strong constitution".