The Cornell link below identifies most of the genetic resistances. Check the varieties you want to grow.

I have grown many heirlooms over the past 25 years with very little disease loss. I attribute my success to soil improvement. Healthy soil provides a balance of nutrients that enable healthy plants. Monitoring soil moisture ensures consistent moisture. Soil organic matter is one vital contribution; compost and green manure addition. A mulch also favors the plants.

Keep in mind that a stressed plant is more likely to attract the pests and diseases.

Good garden practices of management, monitoring and hygiene can reduce the occasions of pests and disease. Proper plant spacing allows ventilation and reduces foliage transfer of pest/disease.

Here is a link that might be useful: Tomato: Disease Resistance Table

In the UK, we have a lot of experience with tomato blight. One year I grew some 64 different varieties of heirloom tomatoes outdoors, zone 8, in a 1/4 acre paddock. Blight hit, predictably, on 8th August after three days of heat and humidity.

However, I found that all the currant varieties proved almost immune to blight and that some of the cherry varieties eg. Broad Ripple Yellow Currant were highly resistant.

I wondered if this was because such varieties are, arguably, closer to their land race progenitors.

I reported my results to the UK's heirloom plant centre Garden Organic who carried out a member trial. Unfortunately, it was inconclusive.