DowDuPont Inc., which will trade on the New York Stock Exchange as DWDP, will replace DuPont on the Dow Jones industrial average on Sept. 1 immediately after Dow Chemical Co. merges with DuPont, parent company of Johnston-based DuPont Pioneer. Dow Jones reported that the move would keep the materials sector on the average. DowDuPont Inc. will have dual headquarters in Midland, Mich., and Wilmington, Del., where its spinoff agriculture company will be based. The ag company will include the DuPont Pioneer campus in Johnston as a major research center.