Erysiphe elevata causing powdery mildew on Eucalyptus urophylla × E. camaldulensis in China

Area of Science:

• Plant Pathology
• Mycology
• Forestry

Background:

• Eucalyptus urophylla × E. camaldulensis, known as Chipper eucalypt, is a vital hybrid for afforestation in China, valued for its cold tolerance, high yield, and disease resistance.
• Clone LH1 is extensively cultivated in South China for its stability and machinability.
• In December 2021, a severe powdery mildew infestation was observed on clone LH1 in Zhanjiang, Guangdong.

Purpose of the Study:

• To identify the causal agent of the powdery mildew outbreak on Eucalyptus clone LH1.
• To confirm the pathogen's identity using morphological and molecular techniques.
• To conduct pathogenicity tests to verify the causal relationship.

Main Methods:

• Morphological examination of fungal structures including hyphae, conidiophores, and conidia.
• Molecular identification using DNA sequencing of internal transcribed spacer (ITS), large subunit rRNA gene (LSU), Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), glutamine synthetase (GS), and RNA polymerase II second largest subunit (RPB2) genes.
• Phylogenetic analysis using Maximum Likelihood (ML) and multi-locus methods.
• Pathogenicity tests on healthy Eucalyptus leaves.

Main Results:

• The pathogen exhibited characteristic hyphae, conidiophores, and conidia consistent with powdery mildew fungi.
• Molecular analysis showed over 99% identity to Erysiphe elevata based on BLASTn searches of ITS, LSU, GAPDH, GS, and RPB2 sequences.
• Phylogenetic analyses placed the fungus within a highly supported clade with E. elevata.
• Pathogenicity tests confirmed the fungus's ability to cause powdery mildew symptoms on Eucalyptus leaves.

Conclusions:

• The powdery mildew disease on Eucalyptus clone LH1 in China was identified as Erysiphe elevata.
• This is the first documented report of Erysiphe elevata causing powdery mildew on Eucalyptus species in China.
• The findings provide crucial information for diagnosing and managing this disease in regional forestry.