Tomato Blight is a common fungal disease that can be serious in wet seasons but less so in dry summers.  It is more likely to attack tomatoes grown outdoors although in some seasons those grown in the greenhouse can also suffer from this disease. 

The first symptoms to be seen are dark brown/black blotches appearing on the leaf edges that quickly spread until the entire leaf is killed.  White fluffy fungal growth may also be present on the underside of the leaf.  Dark patches can also develop on the stem and the green fruit.   The more mature fruit decays rapidly with a dryish brown rot which may not be visible for several days after picking. 

Once blight has a firm hold there is little that can be done other than destroying the affected plants. 

The varieties Fantasio, Lizzano show some resistance to blight.  Crimson Crush is the most resistant variety available to the amateur gardener.