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Abstract
Emerging viral diseases are a growing concern for cotton production in the USA. Cotton leafroll dwarf virus (CLRDV), which causes cotton leafroll dwarf disease (CLRDD), poses a persistent threat to the cotton industry. In this study, we analyzed P0 gene diversity, tissue tropism, and epidemiology of CLRDV, providing critical insights into advancing disease management strategies for Upland cotton (Gossypium hirsutum L) production in Georgia (GA). To optimize diagnosis, we examined CLRDV distribution across cotton tissues. We synthesized cDNA clones of CLRDV and assessed their infectivity via agroinoculation and infiltration under greenhouse conditions, along with aphid-mediated transmission, to investigate disease progression and symptom development. To address the grower’s concern in GA, we evaluated the role of caulimovirid-like endogenous viral elements (EVE-GA) in terminal abortion and yield loss. Additionally, field monitoring was conducted from 2022 to 2024 in on-farm variety trials across Georgia to evaluate the involvement of CLRDV in symptom expression resembling bronze wilt in specific cultivars and associated yield loss. Our findings revealed that the P0 gene of GA isolates exhibited atypical genotypes. Phylogenetic analysis showed that North American isolates form a distinct clade, with cotton and weed species isolates in the USA segregating into two clusters. Tissue tropism analysis detected high viral gene copy numbers in newly growing top branches. No association was found between EVE-GA and terminal abortion, and no significant yield loss was observed in symptomatic plants. Greenhouse studies using virulent aphids and cDNA clones did not result in disease progression or symptom development. Field monitoring revealed spatial and temporal variability in CLRDD incidence and yield loss. Specific cultivars infected at early growth stages exhibited severe wilting and bronzing, with higher viral gene copy numbers than their asymptomatic counterparts, suggesting a role of the virus in CLRDV-induced bronze wilt. Symptomatic plants experienced complete yield loss, whereas asymptomatic plants showed no significant yield reduction. These findings provide critical insights into CLRDD epidemiology and symptomatology, highlighting the need for future research on disease development factors. This knowledge will support breeding efforts and inform disease management strategies to sustain cotton production in the USA.