It is talking about if salt damage is a problem in your situation:
Salt damage is rarely encountered in field situations except under very poor water quality situations. Salt damage may become a problem in pot [container] culture or in hydroponics. Select salt tolerant varieties.
If you are adding synthetic fertilizers, which are chemical salts, frequently, in a container growing situation, the salts can build up. Solutions to that are changing the soil in your container, at least annually, using organic fertilizers like compost etc, flushing lots of water through. And I guess it would in that situation to grow varieties of tomatoes which have been bred to be tolerant of higher level of soil salts.
But honestly when I tried to look up what would be salt tolerant varieties, all I got was information about new GMO tomatoes, which are lab created with recombinant DNA to tolerate really brackish water, salt spray from the ocean etc.
"Salt tolerance is a complex process that is not controlled by a single gene, so attempts at breeding [without GMO techniques] salt-tolerant tomatoes have been unsuccessful. " https://homeguides.sfgate.com/salt-toler ... 53782.html
again that is talking about high salt tolerance like brackish water.
So, although I know what the words mean, I don't know what it means in practice to select salt tolerant varieties, since I couldn't find the existence of any. But it isn't important since 1) growing in the ground you will rarely have problems with excess salt unless you are really pouring on the Miracle Gro, in which case you could stop doing that. 2) growing in containers the problem is solved by changing the soil.