If I want to turn teosinte into corn, using ancient methods like the Native Americans did, then how much time it takes, and what do I have to do?
For the sake of the question, let's assume that time is not a problem for me. Say I live 10,000 years. But of course, I prefer to have maximum efficiency. If I can get the result in 3,000 years, that's better than 5,000 years.
Initially I didn't like this question very much, but I changed my mind when I realized that there is actually ongoing research to do exactly what you propose in order to study just how long it takes to get maize from teosinte.
John Doebley at the University of Wisconsin-Madison has a project ongoing to breed 30 generations of teosinte to be more "corn-like" on a single parameter, the length of the lateral branches.
The first challenge is to find a strain that isn't already contaminated by modern maize - that isn't completely possible, but he selected a strain that has minimal hybridization. You would have to do the same.
Second, you have to plant someplace isolated to further prevent hybridization. Dr. Doebley has a plot in Hawaii for this purpose.
Note that even though this scientist is only selecting over 30 generations, he doesn't anticipate that much of a change (i.e., he doesn't expect to have anything like corn when he is finished), and he is only selecting on a single parameter and furthermore, this parameter was chosen specifically for being easy to score, showing a lot of variation in the existing population, and influenced by a known single gene. Many more generations would be expected to get a product like modern corn. And even domesticated corn has changed significantly over thousands of years of agriculture.
For this answer, I simply reference the project site that I linked above, but in case that link goes dead, here is some literature that the project cited directly:
Beadle, G. W., 1977 The origin of Zea mays, pp. 615-635 in Origins of Agriculture, edited by C. E. Reed. Mouton, The Hague.
Beadle, G. W., 1978 Teosinte and the origin of maize, pp. 113-128 in Maize Breeding and Genetics, edited by D. B. Walden. John Wiley & Sons, New York, NY.
Doebley, J., A. Stec and C. Gustus, 1995 teosinte branched1 and the origin of maize: evidence for epistasis and the evolution of dominance. Genetics 141: 333-346.
Doebley, J., A. Stec and L. Hubbard, 1997 The evolution of apical dominance in maize. Nature 386: 485-488.
Doebley, J. F., A. Stec, J. Wendel and M. Edwards, 1990 Genetic and morphological analysis of a maize-teosinte F2 population: implications for the origin of maize. Proc. Natl. Acad. Sci. 87: 9888-9892.
Iltis, H., 1987 Maize evolution and agricultural origins, pp. 195-213 in Grass systematics and evolution, edited by T. Soderstrom, K. Hilu, C. Campbell, and M. Barkworth. Smithsonian Inst. Press, Washington, D. C.
Wang, R.-L., A. Stec, J. Hey, L. Lukens and J. Doebley, 1999 The limits of selection during maize domestication. Nature 398: 236-239.
Wilkes, H. G., 1967 Teosinte: the closest relative of maize. The Bussey Institute, Harvard University, Cambridge.
Wilkes, H. G., 1977 Hybridization of maize and teosinte in Mexico and Guatemala and the improvement of maize. Econ. Bot. 31: 254-293.
