Contraction in the output of coal, natural gas, and fertiliser pulled down the growth of the country's eight core sectors to 2.6 percent in December 2012.Official data released yesterday said that the key infrastructure sectors had grown 4.9 per cent in December 2011. However, the growth in December was better than November's growth of 1.6 per cent.During the April to December 2012 period, growth in these industries slowed to 3.3 per cent, from 4.8 per cent in the same period of the previous year.