Molecular Characterization and Biological Properties of Iris Yellow Spot Virus Infecting Onion in Irrigated Fields

Abstract

Iris yellow spot virus (IYSV) is an economically important tospovirus causing severe yield and quality losses in onion cultivation, particularly under irrigated production systems where vector populations are favored. The present study aimed to investigate the molecular characterization and biological properties of IYSV infecting onion fields. Field surveys were conducted in irrigated onion-growing areas, and symptomatic samples exhibiting chlorotic lesions, necrotic streaks, and leaf tip dieback were collected. Total RNA was extracted and subjected to RT-PCR amplification targeting the nucleocapsid (N) gene of IYSV. Sequencing and phylogenetic analysis confirmed the identity of the virus isolates and revealed their close relationship with previously reported IYSV strains from major onion-producing regions. Molecular variability among isolates was relatively low, suggesting a conserved genetic structure within local populations. Biological studies indicated that disease severity was closely associated with thrips activity, particularly Thrips tabaci, which acts as the primary vector. Virus transmission efficiency was influenced by environmental factors such as temperature and irrigation frequency, which indirectly affected vector population dynamics. Infected plants exhibited reduced photosynthetic efficiency, stunted growth, and significant bulb yield reduction. Mixed infection patterns were occasionally observed, indicating the potential for synergistic interactions with other viruses. The study highlights the importance of integrating molecular diagnostics with field-based epidemiological observations for accurate characterization of IYSV. Overall, the findings provide important insights into the genetic identity and biological behavior of IYSV in onion agroecosystems and emphasize the need for effective vector management and use of virus-free planting material to reduce disease incidence in irrigated cultivation systems.