The retail sector is lower for the second day in a row following Marks & Spencer's Christmas trading update.Sales rose 2.6% in the 13 weeks to 26 December and by 2.3% in the UK, but echoing comments from fellow clothes retailer Next yesterday, M&S chairman Stuart Rose said: 'We expect the trading conditions over the coming year to remain challenging as a result of continuing economic uncertainty.'Next, which yesterday fell after its trading statement, is slightly higher today.Food retailers are also lower, including Sainsbury's, whose third quarter trading statement is due tomorrow.Top performing sectors so far todayAutomobiles & Parts 2,871.14 +2.33%Fixed Line Telecommunications 2,035.58 +1.33%Forestry & Paper 3,845.37 +1.33%Chemicals 4,674.14 +1.10%Aerospace and Defence 3,161.21 +0.79%Bottom performing sectors so far todayIndustrial Metals 5,110.01 -2.18%General Retailers 1,753.26 -1.59%Health Care Equipment & Services 3,477.99 -1.42%Food & Drug Retailers 4,664.63 -1.32%Personal Goods 10,809.25 -0.99%