The pinewood nematode (PWN), Bursaphelenchus xylophilus, infects susceptible pine species and causes pine wilt disease. After reaching the pine’s internal tissues, the PWN feeds on the resin canals and vascular tissue and quickly reproduces to large populations, causing a cessation of resin flow and embolism events in the tree’s water column. At the pine leaves, the low water supply heavily damages the biochemical reactions of photosynthesis, reducing the net photosynthetic rate and stomatal conductance. Impaired photosynthesis leads to the first visible symptoms of pine wilt disease, namely, the yellowing and drooping of pine needles. In vitro cultures are useful tools to research changes in fine biochemical reactions because they allow for reproducibility and genetic homogeneity. In the present work, in vitro maritime pine (Pinus pinaster) shoot cultures were used to assess changes in the concentration of photopigments, i.e., chlorophyl a and b, carotenoids, and the stress-related anthocyanins, by resorting to spectrophotometry techniques. Infection with the pinewood nematode led to a 30% reduction in leaf concentrations of chlorophyl A and a 50% reduction in chlorophyl B. Carotenoid concentrations increased by70 %, while no changes were observed for anthocyanins. This preliminary study allows for gauging the impacts of pinewood nematode infection of pine at the initial stages of pine wilt disease as a contribution to developing an early detection method for this phytoparasite.