Host-Dependent Cytopathological Responses to Beet Curly Top Virus Infection in Four Plant Species

Beet curly top viruses (BCTVs) are highly devastating viral pathogens affecting a wide range of plant species worldwide and are transmitted only by leafhoppers in the genus Circulifer. During viral infection, host plant cells undergo morphological changes known as cytopathic effects (CPEs). This study investigated CPEs induced by BCTVs infecting four plant hosts: tomato, pepper, sugar beet, and hemp. BCTV infection resulted in severe stunting, leaf curling, and yellowing, leading to reduced photosynthetic capacity and yield losses. Transmission electron microscopy of ultrathin leaf sections revealed that chloroplasts were the universal primary target of BCTV damage across all four hosts, consistently exhibiting severe structural disruption, while starch grains and vacuoles were also affected. Notably, host-specific ultrastructural alterations were observed: enlarged chloroplasts with disrupted grana stacks and small stromal vesicles in BCTV-Wor-infected tomato and hemp, swollen chloroplasts with disappeared grana and disorganized thylakoids in BCTV-Svr-infected sugar beet, and unidentifiable grana structures in BCTV-PeYDV-infected pepper. These alterations did not correlate with virus strain, suggesting that host-specific inducible defense mechanisms play a greater role than strain identity. This is the first study to highlight the diverse ultrastructural impacts of BCTVs across plant species, improving understanding of host–virus interactions and aiding development of control strategies to safeguard global food security.