Posted: 13/08/2012 at 17:58
Dipadee, I don't know how big your tubs are but it's a good idea to replace the soil (or mix) every year anyway. A season of growing depletes the growing medium of its nutrients and goodness. Starting a new season afresh gives the plants a healthy head start.
There a varieties coming onto the market that are being sold as blight-resistant. That doesn't mean they won't get fungal disease, just that they will - it is claimed - battle on a bit longer when they have it. Honestly, if you spray preventively, or if you don't like spraying and just observe good housekeeping practice at the least, any tomato plant will battle on against fungal disease.
In saying that, I'm talking about the most common fungal problems - Early Blight, Septoria Leaf Spot, etc. Keeping plants well spaced to aid air circulation, removing affected foliage as soon as symptoms appear, keeping the foliage dry and judiciously removing excess foliage to aid air circulation will all help. It takes a very long time for the common fungal problems (above) to kill a tomato plant.
Something like Late Blight, on the other hand, will kill a plant within a week. There's no such thing as resistance to Late Blight.