The exit of frontman Dalton Philips at Wm Morrison and signs of improving sales trends at the UK grocer were welcomed by the market on Tuesday, with food retailers topping the risers list in London.Well-received trading updates from the likes of Greggs also provided a boost to the food sector, while ASOS sparked a rise among the wider retail category, though upside was limited by a disappointing outlook from high street department-store Debenhams.The share price of supermarket group Wm Morrison jumped over 4% following the news that Philips has been axed after five years.Deputy chairman Andrew Higginson said: "In the next chapter of Morrisons development, we need to return the business to growth. The board believes this is best done under new leadership."The news came as Morrison reported a 3.1% decline in like-for-like (LFL) sales excluding fuel in the six weeks to 4 January, slightly better than the 3.8% drop expected by analysts.Industry data from Kantar also showed that increased consumer spending over Christmas helped the grocery market grow at its fastest rate since August 2014."Shoppers chose to buy a little bit more this Christmas compared with last year, a trend which has pushed sales growth up to 0.6%. This is low in historical terms, but a rally for the supermarkets compared with recent months," Kantar said.Shares of Tesco and Sainsbury's were also rising nearly 4%.A very strong post-Christmas update from sausage-rolls-and-sandwiches retailer Greggs led management to boast that full-year results will beat current expectations, causing the stock to sizzle nearly 9%. Christmas LFL sales were up 8.2%.Meanwhile, ASOS surged 8% after reporting a 15% rise in retail sales over Christmas, driven by a 27% jump in sales in the UK. Broker Shore Capital said the growth in its domestic market would encourage investors following a tough 2014, which saw its share price plummet.Bucking the trend on Tuesday was high street department store Debenhams whose shares dropped nearly 7% after revealing that full-year margins will be at the lower end of guidance despite a record sales performance over Christmas. Top performing sectors so far todayFood & Drug Retailers 3,037.29 +3.55%Automobiles & Parts 8,365.60 +2.67%Electricity 9,082.95 +1.68%Financial Services 8,517.22 +1.62%General Retailers 2,950.36 +1.60%Bottom performing sectors so far todayHealth Care Equipment & Services 6,615.33 -1.51%Mining 13,699.02 -0.94%Technology Hardware & Equipment 1,186.85 -0.66%Aerospace and Defence 4,752.73 -0.18%