[lenht]

I have about 30 outdoor growing tomato plants, several of which have produced fruit that has gone from green to brown without turning red. I was given these as small plants by a friend who had cultivated them from his own seeds. It is not restricted to one plant but to several, all of which appear to be different varieties. The crop was sparayed against blight and the plants themselves appear healthy.
Anyone got any ideas what is wrong  :?

[iwantanallotment]

Could they possibly be a brown/mahogany variety/varieties, ie Russian Black Cherry, etc?

[SalJ1980]

Hi Lenht and welcome to the forums!    No idea personally as I only have one tomato plant outside (it wouldn't fit in the greenhouse) and - fingers crossed - it's fine so far.

Someone else will be along shortly with the answer!

[Trillium]

If everything else is healthy, then I'd go with what iwantanallotment suggested - that somehow all your friend's seeds got crossed with the dark brown/rust coloured, and more dominant, type tomatoes which are mostly Russian in origin. To save your own seeds you must be diligent about covering the plants from wind and bees who can easily cross pollinate what you don't want.

Try one of each different variety and see how they taste.

[hotterotter]

could be Blossom End Rot or something like that, its caused by pottasium deficiency

[DD.]

could be Blossom End Rot or something like that, its caused by pottasium deficiency

Not if it's the whole fruit that's affected.

B.E.R. is caused by a calcium deficiency and can infact be stimulated by an excess of potassium.