BANGKOK, March 8 (Reuters) - Southeast Asian indexes retreated on Tuesday tracking weakness in Asia, as investors in the region's emerging markets cashed in on recent gains. Singapore's key Straits Times Index was down 0.6 percent, extending Monday's decline. The fall was led by recently rallying banks, including DBS Group Holdings which shed 1 percent. Asian shares, led by China , fell as investors took profits after a month-long rally and ahead of major central bank meetings, with the
