Phenotypic Changes in Pinus thunbergii, Larix kaempferi, Picea koraiensis, and Abies holophylla Seedlings Inoculated with Pine Wilt Nematode: Revealing the Resistance

Bursaphelenchus xylophilus (pine wood nematode, PWN) has been present in China for over 40 years and has spread to northeast China, where native pine species are key components of the local top community. Pinus thunbergii is known to be susceptible to PWN among local conifer species, whereas research on PWN&rsquo:s pathogenicity in Larix remains limited. Furthermore, there are no research reports on PWN infestation in Picea and Abies species within China. This study conducted a detailed analysis of phenotypic changes and temporal spectral reflectance variations in four conifer species in northeast China&mdash:P. thunbergii, Larix kaempferi, Picea koraiensis, and Abies holophylla&mdash:following artificial inoculation with PWN. The aim of this study is to establish a theoretical basis for identifying the potential hosts and threats of PWN. The study incorporated a 60-day post-inoculation observation period to systematically monitor and compare temporal changes in external morphology, disease susceptibility (incidence and mortality rates), spectral reflectance, and the normalized wilt index (NWI) in 2&ndash:3-year-old seedlings of P. thunbergii, L. kaempferi, P. koraiensis, and A. holophylla after inoculation with PWN. The results showed that P. thunbergii displayed the earliest infection symptoms, followed by L. kaempferi, A. holophylla, and finally P. koraiensis. After inoculation, P. thunbergii was the first to experience mortality, followed by L. kaempferi, P. koraiensis, and A. holophylla. Following inoculation, P. thunbergii exhibited the earliest significant increase in NWI (p &lt: 0.001), followed by L. kaempferi and A. holophylla: P. koraiensis showed the latest increase (p &lt: 0.001). In conclusion, the experiment identified P. koraiensis as having the strongest resistance to PWN among the four species, followed by A. holophylla. P. thunbergii showed the weakest resistance, while L. kaempferi exhibited moderate resistance. The ranking of PWN susceptibility for the four conifer species, from highest to lowest, is as follows: P. thunbergii, L. kaempferi, A. holophylla, and P. koraiensis.