Mission: Lower Lats
Bodybuilders usually have a hard time getting those wide lower lats, while they have no trouble with upper lats. You will be pleasantly surprised to hear that you can easily get great lower lats by simply reversing your regular grip. Indeed underhand grip makes all the difference and helps you work some new muscles during your regular rowing exercise.
Your lower lats will work to greater extent when you keep your hands in underhand position while pulling your arms back. In fact, upper lats are utilized during exercises which involve pulling elbows to the sides (for example wide-grip rows or pull-downs). On the other hand, your lower lats will work for the most part if you keep your elbows close to your sides, like in underhand pulldowns or rows.
If you want to develop your entire back then make sure to have various hand positions when doing deadlifts, such as overhand, reverse, mixed grip (one palm backhand and the other forward), and neutral. Reverse grip provides more movement. For example, having reverse grip while doing lat pulldowns and barbell rows will greatly engage your lower lats and involve much greater range of motion.
If you want to boost those effects even more, then narrow the grip. Having your hands closer in reverse grip position will help you stretch your lats even to a greater extent and also pull your elbows even further back.