I would say that love is another theme in Fences--not merely the obvious expression of love between Troy and Rose, or that which Troy expresses toward Raynell in her infancy, but also the perceived scarcity of love and how that perception affects the characters' behavior.
Troy does not demonstrate love to his son Cory, prompting Cory to ask if Troy loves him. Troy is too frustrated by his circumstances to think of anything beyond bare necessities. He is angered by the question and says that, if he did not love his son, he would not work to feed and clothe him. In Troy's mind, there is no time or need for emotive expression, only for the performance of duty, which, in Troy's mind, suffices. His own father had not performed his duty of caring for or guiding his son. Troy recalls a disturbing instance on the Southern plantation of his youth when his father takes Troy's thirteen-year-old girlfriend for himself.
Troy is not much different toward Lyons, though his relationship with his eldest son is characterized more by tolerance than the resentment he directs at Cory. Lyons pursues his art--jazz--because it is something that he loves and it brings him joy. However, his pursuit of jazz causes him to rely on Troy for money. Troy, frustrated by his own unfulfilled ambitions and dreams, tries to dissuade his sons from the pursuit of their own. His inability to love his sons fully makes him unwilling to support their ambitions, despite his failures.