  In the studies of plant infections, the plant immune response is known to
play an essential role. In this paper we derive and analyse a new mathematical
model of plant immune response with particular account for post-transcriptional
gene silencing (PTGS). Besides biologically accurate representation of the PTGS
dynamics, the model explicitly includes two time delays to represent the
maturation time of the growing plant tissue and the non-instantaneous nature of
the PTGS. Through analytical and numerical analysis of stability of the steady
states of the model we identify parameter regions associated with recovery and
resistant phenotypes, as well as possible chronic infections. Dynamics of the
system in these regimes is illustrated by numerical simulations of the model.
