Taxation on purchase of capital asset for a consideration less than stamp duty value

Assessee has purchased a capital asset for Rs.50000/- in year 1979 but no purchase deed was made at that time. He paid all consideration in 1979. In F.Y.2013-14 he made purchase deed for the asset indicating consideration Rs.50000/- paid in 1979; but now Stamp duty value of the property is 50 lakh. Please guide me about tax liablity of assessee/buyer in such a case.