Rental accounting

Dear all,

       Is that mandatory to account rent on straight line basis as per AS-19 if there has been any rental increment as per pre-agreement???

For example:

If there has been a rental agreement between A&B for a building where as A ,owner and B, being tenant.if the monthly rental for fy 2013-14 has been 14000/- ,and an increment of RS.1000/- from the expiry of 1 yr. what should be the rent to be accounted in the books of B whether it is Rs .14000/- p.m or else in the other way????