This year seems to have been my worst for a while in the greenhouse, with tomatoes, cucumber and chillis. Only one cucumber so far whereas last year I had them by the barrow load. I grew three varieties of tom; tigerella, ailsa craig and black cherry. I am just starting to get some ripe ones now, but the leaves on the black cherry have started to turn brown and powdery. I have removed most of the branches, but the tomatoes are only lasting a few days after I pick them and they don't taste great. I really love BC toms normally I've grown them for the last 3 or 4 years, keeping the seed for next year. The tigerella and ailsa craig that are growing next to the black cherry, don't seem to be affected at all. The strange thin is these were the strongest plants from seed and were twice the size of the others initially.
Is this something I have caused by keeping the seeds from the previous year or are black cherry tomatoes more susceptible to blight?