Distribution of Papaya Ring Spot Virus Infecting Papaya in Kerala, India

In the midst of the rising interest of papaya cultivation in Kerala, it is inevitable to study the current status of the Papaya ring spot disease in the state. Knowing the severity and distribution of PRSV isolates, causing ring spot disease, helps in the better formulation of effective management strategies against it. Purposive sampling surveys carried out in 2021-22 across five agro ecological units (AEUs) of Kerala, recorded papaya ring spot disease incidence (PRSD) ranging from 50 to 100 per cent in the cultivated areas with vulnerability index of 33.54 to 98.22. Highest disease incidence was recorded from AEU 8- Southern Laterites: Thiruvananthapuram (100.0%) and highest vulnerability index was recorded from Kalliyoor (98.22). Twenty symptomatic samples tested positive for PRSV in double antibody sandwich- ELISA (DAS-ELISA) using PRSV polyclonal antiserum. RT-PCR using coat protein gene specific primers RKJ 52 and 3 yielded amplicons of size approximately ~890bp in all the samples. Virulence of the Kerala isolates was evaluated based on the symptom expression, disease incidence and vulnerability index, upon mechanical transmission of PRSV on two months old papaya plants (variety- Red Lady). PRSV isolate from Kalliyoor (TVM1) inoculated on papaya plants expressed chlorosis, mottling, malformation of leaves and stunting with 96.80 vulnerability index. Maximum vulnerability index and severe symptoms including stunting in the inoculated plants were observed in isolates from southern and central Kerala, which include Thiruvananthapuram, Alappuzha and Thrissur had the most virulent PRSV isolates compared to north Kerala.