Microbial community differences between healthy and Ustilago-infected oats

Ustilago, a pathogenic fungus, poses a serious threat to oat growth and yield. However, the species composition, abundance, and distribution of microbial communities in Ustilago-infected oats remain poorly characterized. In this study, we conducted 16S rRNA and internal transcribed spacer (ITS) amplicon sequencing and biochemical assays to compare microbial profiles and physiological traits between healthy (n = 60) and Ustilago-infected oats (n = 60). Our analyses revealed higher bacterial diversity in healthy oats, particularly in the spikes and stems. Significant shifts in microbial community structure were observed across all tissues in diseased plants. While the microbiome of healthy oats predominantly comprised beneficial bacteria, including Exiguobacterium indicum, infected plants were largely colonized by pathogens, including Ustilago hordei, Pyrenophora chaetomioides, and Curtobacterium flaccumfaciens pv. flaccumfaciens, suggesting the occurrence of disease-driven microbial restructuring. Functional predictions indicated that enriched pathways were primarily associated with metabolism, followed by genetic information processing and environmental signal transduction. Malondialdehyde content was significantly lower in most healthy oat tissues compared to Ustilago-infected oats, whereas the activities of the antioxidant enzymes superoxide dismutase and peroxidase were markedly higher. These results implied that Ustilago infection induced severe oxidative damage to membrane systems, likely compromising the plant's ability to scavenge superoxide ions and hydrogen peroxide, thereby reducing overall plant health.