Yet the 75-year-old farmer from southwestern Indiana will face off Tuesday against the world’s largest seed company, Monsanto, in a Supreme Court case that could have a huge impact on the future of genetically modified crops, and also affect other fields from medical research to software. At stake in Mr. Bowman’s case is whether patents on seeds — or other things that can self-replicate — extend beyond the first generation of the products. It is one of two cases before the Supreme Court related to the patenting of living organisms, a practice that has helped give rise to the biotechnology industry but which critics have long considered immoral. The other case, involving a breast cancer risk test from Myriad Genetics, will determine whether human genes can be patented. It is scheduled to be heard April 15.