Differential polynomial rings over rings satisfying a polynomial identity

Let $R$ be a ring satisfying a polynomial identity and let $\delta$ be a derivation of $R$. We show that if $N$ is the nil radical of $R$ then $\delta(N)\subseteq N$ and the Jacobson radical of $R[x;\delta]$ is equal to $N[x;\delta]$. As a consequence, we have that if $R$ is locally nilpotent then $R[x;\delta]$ is locally nilpotent. This affirmatively answers a question of Smoktunowicz and Ziembowski.