Please pardon this lengthy excursion into tobacco genetics.
The most effective selection conditions are those that kill a relatively high percentage, but not all, of the plants. But this assumes some degree of diversity in the genetics of a variety. Unfortunately, all stable varieties of tobacco are nearly homozygous (zero heterozygosity). That is to say, there is no handy drought resistance gene hiding in some of them, so there should be little opportunity for finding individual specimens that are more fit than others of the same variety. You would be waiting for spontaneous mutations.
It is possible to get more rapid adaptation under milder stress, but this tends to be epigenetic, and passed only to the next generation. Actual, genetic change under slight stress requires way more generations that a human lifetime. You can fiddle with intentional crossing of varieties, with selection for your desired trait, but that much faster process still takes in the neighborhood of seven or more years.
All the legends about local adaptation are mostly hooey. As an example, Oriental varieties are said to be more drought tolerant, and need less fertilizer, whereas the truth is that inadequate water and insufficient soil nutrients (together with spacing them way too close together) cause Oriental varieties to grow and taste the way that met the expectations of Ottoman growers and their tobacco consumers. If you give Orientals "American" spacing in the ground, "American" fertilizer and "American" irrigation if needed, those delicate, 3-foot plants with small leaves grow over 7 feet tall, with relatively large leaves--but they don't have those Turkish aromas and leaf characteristics we normally associate with Orientals.
Conclusion: water your plants.
Bob
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