Oct 28 (Reuters) - Shares of automobile insurance startup Root Inc fell nearly 4% in their market debut on Wednesday, marking a weak open for the firm after it raised about $724 million in its initial public offering. The stock opened at $26, compared to its IPO price of $27 per share. (Reporting by Ambar Warrick in Bengaluru; Editing by Ramakrishnan M. And Maju Samuel)