Adverse pine wilt disease expansion forecasts must be met with rapid advances in tools to fight against this disease, such as genetic breeding. The optimal approach for breeding more resistant trees to B. xylophilus, causative agent of this disease, is to use the most virulent isolates in inoculation assays.

Different inoculation experiments were conducted on Botrytis cinerea cultures, along with P. pinaster and P. radiata branch sections and seedlings. Seven virulent isolates of diverse geographic origin (USA745 from USA, KA4 and S10 from Japan, Pt52T and Pt72CH from Portugal, SpPO1 and SpSA1from Spain) were used in the experiments. The main aim of this work is to investigate differences among the seven isolates.

Results from the experiments showed significant differences among B. xylophilus isolates. On fungal culture, the isolate from USA showed the highest multiplication rate. Both seedling inoculation and branch sections experiments pointed to the Portuguese isolate Pt52T and the Spanish SpPo1 as the most virulent to P. pinaster. Conversely, higher numbers of Pt72CH isolate passed through P. pinaster branch sections. The most virulent isolate for P. radiata was the Japanese S10, though it only showed significant differences in mortality when compared to the Spanish SpSA1. These results suggest that B. xylophilus have differential host specificity.