Contamination-Free Genome Assembly of Podosphaera xanthii Reveals Signatures of Obligate Biotrophy.

Podosphaera xanthii is an obligate biotrophic fungus responsible for powdery mildew disease in cucurbits. Its strict host dependency has hindered genomic studies due to challenges in isolating pure fungal DNA. In this study, we present a high-quality genome assembly of P. xanthii Race 1 using PacBio HiFi reads, Illumina short reads, and RNA-seq data, combined with stringent in silico filtering to remove host and microbial contaminants. The final assembly spans 151.7 Mbp across 67 scaffolds with 80.04% repeat content and 7,452 predicted genes. Functional annotation revealed effector-related features and gene categories consistent with biotrophic lifestyles. Comparative analyses with other P. xanthii genomes exposed variable contamination levels, underscoring the importance of strict data curation. Our work provides a reliable genomic reference for P. xanthii, enabling future research on pathogenicity, evolution, and host interactions in powdery mildew fungi and contributing to broader understanding of obligate biotrophic adaptation.