Powdery mildew in Eucalyptus spp. clonal mini gardens in Uruguay

Abstract

Powdery mildew is a fungal disease that poses a significant threat to global Eucalyptus cultivation; yet the species-level identity of causal agents often remains unresolved due to the limitations of morphological diagnosis. Here, the first estimates of powdery mildew incidence in Eucalyptus clonal mini gardens in Uruguay is provided, and the first approach of species identification within this system is presented. Surveys across three industrial nurseries revealed an overall powdery mildew incidence exceeding 70%, with noteworthy temporal variation and differences among clones. Molecular analyses, using DNA-based identification tools targeting the ITS and LSU rDNA regions, confirmed the presence of Podosphaera pannosa, previously identified in Eucalyptus grandis infections based only on morphological characteristics. Furthermore, this study reports, for the first time, P. aphanis, P. cfr. ruborum and an undescribed Podosphaera species infecting Eucalyptus dunnii in Uruguay. The results highlight the strong influence of host genotype on disease dynamics, with some clones exhibiting consistently lower susceptibility. These findings highlight the importance of integrating genetic resistance, cultural measures, and targeted fungicide applications into management strategies, as well as the critical need for active phytosanitary monitoring to track pathogen spread and inform control efforts. This work lays the foundation for future epidemiological studies and breeding programs aimed at mitigating the impact of powdery mildew on Uruguay’s commercially vital Eucalyptus forestry sector.

Keywords: Podosphaera, Forest nursery, Phylogenetic analysis