Among their responses to microbial infection, plants deploy an arsenal of antibiotic natural products. While these historically have been identified on the basis of their antibiotic activity in vitro, this leaves open the question of their relevance to defense in planta. The vast majority of such natural products from the important crop plant rice (Oryza sativa) are diterpenoids whose biosynthesis proceeds via either ent- or syncopalyl diphosphate (CPP) intermediates, and which were isolated on the basis of their antibiotic activity against the fungal blast pathogen Magnaporthe oryzae. However, rice plants in which the gene for the syn-CPP synthase Os-CPS4 is knocked-out do not exhibit increased susceptibility to M. oryzae. Here it is further shown that knocking-out or knocking-down Os-CPS4 actually decreases susceptibility to the bacterial leaf blight pathogen Xanthomonas oryzae. On the other hand, knocking-out or knocking-down the gene for the ent-CPP synthase Os-CPS2 is found to increase susceptibility to both M. oryzae and X. oryzae, while over-expressing Os-CPS2 decreases susceptibility to both. Despite the secretion of diterpenoids dependent on Os-CPS2 or Os-CPS4 from roots neither knock-out exhibited significant changes in the composition of their rhizosphere bacterial communities. Nevertheless, rice plants allocate substantial metabolic resources towards syn- as well as ent-CPP derived diterpenoids upon infection/induction. On the basis of this observation further investigation was carried out, revealing that Os-CPS4 plays a role in fungal non-host disease resistance. Thus, as exemplified here with rice diterpenoids, examination of metabolic allocation provides important clues into physiological function.