TOKYO, May 1 : Toyota is expected to report a fourth successive year-on-year decline in quarterly operating profit next week, as rising material and labour costs and the impact of U.S. tariffs offset strong demand, particularly for hybrid vehicles. The world's biggest automaker is forecast to post operating profit of 813 billion yen ($5.17 billion) for the January-March quarter, down 27 per cent from a year earlier, according to the median estimate of seven analysts surveyed by LSEG. That would