Please go to the tomato forum and review the FAQ's link at the top of the page. There is also a current thread on cross pollination in the tomato forum.

In a nutshell, the fruit is not affected even if two varietes cross. The seed can be affected so if you grow seed of Brandywine for example, you could wind up with a regular leaf plant. Tomatoes normally cross at a relatively low rate of about 5%. Under some conditions though, this can be much higher.

Fusion

I intend to plant Brandywine tomatoes this year( I bought some plants today).
I was just told that this tomato was very susceptible to disease (some kind of mold?) and that if this disease infected my garden then I would have to abandon that plot of ground because it would infect other plants.. Does any of this make sense?

Once again, Joanelaine, I think the best advice would be to go to the Tomato forum and do a search of "brandywine soil disease" or "brandywine soil blight" (without the quotation marks).

Brandywine tomatoes are a HUGELY popular heirloom but I've not grown it because of my short season. There are plenty of newer disease-resistant hybrid varieties. However, I think that it would be far more likely that diseases currently in your garden soil would be more of a threat to your Brandywine than any possible jeopardy your tomato plants would have for future gardens.

Steve

I have been growing Brandywines for eight or ten years now, and I have never seen any indication of disease.
My Brandywines are the most robust of all the varieties I grow, and they give the most fruit

I am growing Brandywine right next to Beefmaster hybrid. I have never had a problem mixing heirloom and hybrid varieties in the same bed.

Well, I didn't think that crossing was likely either and have regularly saved heirloom tomato seed. I knew that there was some question regarding currant tomatoes was all.

However, Zeedman did a fine job on GW's veggie forum recently explaining how it can and does take place. As notes Zeedman - -

"However, some tomatoes are very prone to crossing:
(1) Potato-leaf varieties
(2) Currant tomatoes
(3) Double blossoms of large tomatoes (usually some of the first of the season)
(4) Varieties whose blossoms have a protruding style/stigma"

Steve

Here is a link that might be useful: How did Great . . . Grandmother avoid crosses?