If you are not saving seed, it does not matter if the plants cross pollinate. The presently growing plant is unaltered. Only its seed is crossed.
Even with active effort to cross N. tabacum and N. rustica, most attempts fail. When seed is successfully produced, most of it is sterile. I don't know what size seed such a cross would yield.
I wonder why it is the seeds would be sterile? Its funny how some things just won't go together even though one would think they would.
Don't misconstrue the fact that I've read this article as evidence I understand it.
Nicotiana tabacum and N. rustica are both tetraploid. Animals are diploid. We get one set of DNA from each parent. 1+1= "di-ploid", whereas with tobacco, they get two sets of dna from each parent so 2+2= 4 (tetra)ploid.
The thing is, there are tetraploid Nicotiana species and there are diploid Nicotiana species. The tetraploid species arose from the successful mating of diploid species in the wild. Since this happened a long time ago, and because the tetraploids have a lot of extra redundant DNA, they've gradually lost unnecessary parts of it. This helps scientists determine how long ago the species began. They also know which diploids are their ancestors.
The immediate ancestors of rustica and nicotiana are very different from one another. Their common ancestor would have been millions of years ago. There has just been too much time for them to change both before and after tetraploidization for the plethora of chromosomes to match up in a meaningful manner that when asked to divide again (when making pollen, and eggs), that they would end up not just with useful pairs, but in their case useful quads when they mate (seed stage).
This blanket is a necessity. It keeps me from cracking up. It may be regarded as a spiritual tourniquet. Without it, I'd be nothing, a ship without a rudder. - Linus
I'm thankful for the short answer cause that other shit still has me asking myself WTF did I just read. Once again thank you Bob.