Question
Leaves of my apple trees are turning yellow resulting in premature defoliation and in fruit dropping.

Answer
Vivek:
Many things can cause these symptoms. Be sure first that you have plenty of moisture in the soil for the trees.  Also, consider examining the trunks for any loose bark or damages. You may need to have someone to make a house call to see your trees in person- it can be very difficult to make a diagnosis w/o visiting them.

Regards
Steve