Phytophthora pseudocryptogea Drives Dieback in Cycas revoluta: Comparative Pathogenicity of Three Phytophthora Species

Phytophthora pseudocryptogea is increasingly recognized as a significant threat to Cycas revoluta cultivation in Mediterranean nursery systems. This study assessed the pathogenicity and relative aggressiveness of P. pseudocryptogea, P. nicotianae, and P. multivora through controlled stem-wounding and soil-infestation assays supported by longitudinal ANOVA models and post hoc comparisons. The results show that P. pseudocryptogea is the only species capable of infecting and colonizing C. revoluta, showing rapid symptom onset, high disease severity, and consistent re-isolation from symptomatic tissues. Conversely, P. multivora and P. nicotianae failed to induce significant symptoms and were statistically indistinguishable from the control across all inoculation methods. Time-series analyses revealed clear species-specific virulence trajectories, highlighting differences in pathogenic behavior among taxa. The findings support P. pseudocryptogea as an emerging pathogen in Mediterranean nursery environments and emphasize the importance of integrating longitudinal analytical frameworks to improve the resolution of pathogenicity assessments.