Are you saving seeds for later planting? If not then it doesn't matter.

But in general, since tomato blooms are self-fertile and many pollinate themselves before or just after opening, cross pollination is relatively low.

There is a FAQ here about this issue.

Dave

Here is a link that might be useful: Growing Tomatoes FAQ

I was thinking about saving seeds but after reading that link, I would have to grow out a lot of seeds to know if I got any crosses and I don't have the room to do that.

2 of my varieties are F1 hybrids, so that would further complicate the situation. I need more land!

Yes, if you want to save seeds and you want only 100% assurance of purity then stick with OP varieties (not hybrids) and plan to bag some blooms for seed purity.

Personally I (and many others who save seed) are content with the natural 95% seed purity of OP varieties so don't bother with bagging blooms.

Dave

Actually, I was hoping for some crosses just to see what they would produce. All of my varieties are supposed to be good tasting - Marglobe, Rutgers, Ramapo, Moreton - and I thought it would be fun to grow out a cross. But now I see that there is no way to tell if you got a cross unless you hand cross them.

Not only that, but you usually don't know what crossed with what, especially if the two parents are of the same color.

The degree of purity really relates to what you want to do with the seeds. If for just home use, not a problem, if you want to trade seeds or make seed offers or even SSE list them then more thought is perhaps needed.

over the years I/ve listed hundreds of varieties in the SSE Yearbook and some times I can distribute 100's of seeds for one variety before an offtype appears.

And that's because just one unfertilized ovule in the tomato ovary can be cross pollinated and that's why I use many fruits from at least two plants of the same variety for seed processing, b'c it dilutes out any X pollinated seeds.

And of those many hundreds of varieties I've SSE listed, or indeed of the ones I've offered in free seed offers I know of less than 20 all told that were X pollinated to one degree or another.

And I don't bag blossoms and I don't isolate geographically. Until 2005 I was growing hundreds of plants and varieties each season and no way was I going to bag blossoms, but in the SSE listed ones as well as the ones in my free seed offers I state that seed purity is not guaranteed.

Carolyn

Thanks, for the info. I think if I want to cross-pollinate, I will investigate how to do it by hand.

Carolyn, do you know what the result would be if I crossed Marglobe with Rutgers since Marglobe is one of the parents of Rutgers? In other words, if Marglobe is one of the parents of Rutgers, shouldn't 50% of the genes of Rutgers be from Marglobe? Then if I crossed Rutgers with Marglobe, would I now have a hybrid that was 75% Marglobe genes and 25% JTD genes (the other parent of Rutgers)?

Thanks, for the info. I think if I want to cross-pollinate, I will investigate how to do it by hand.

*****

I'll give you an excellent link below and you can read about how to create a hybrid as well as how to save seeds, now the F2 seeds from that hybrid and make selections from those plants and same in further generations When you open up the site click on CULTURE and look at the relevant links belowoe. There's lots more at that site so take some time to look around.

(Carolyn, do you know what the result would be if I crossed Marglobe with Rutgers since Marglobe is one of the parents of Rutgers? In other words, if Marglobe is one of the parents of Rutgers, shouldn't 50% of the genes of Rutgers be from Marglobe? Then if I crossed Rutgers with Marglobe, would I now have a hybrid that was 75% Marglobe genes and 25% JTD genes (the other parent of Rutgers)?

It isn't clear to me what your goal is. You can get JTD seeds at Victory seeds and just cross with Marglobe and since Rutgers was a selection from that intial cross there's no way of predicting what proportion of genes of either parent will be an any one selection.
Carolyn

Here is a link that might be useful: Keith Mueller's website