Epidemiological studies on the incidence of papaya ringspot disease under Indian sub-continent conditions

Abstract

Papaya (Carica papaya L.) is a commercially important fruit crop cultivated worldwide due to its nutritional and medicinal values. Papaya ringspot disease (PRSD), caused by the papaya ringspot virus (PRSV), poses a significant threat to papaya cultivation, resulting in substantial yield losses. In this study, two independent field experiments were conducted at Bagalkote located in the Northern Dry Zone of Karnataka. The first experiment aimed to determine the optimal planting month for papaya to effectively manage PRSV disease. The second experiment aimed to determine the susceptibility stage of papaya to PRSV infection. The results revealed that planting papaya in March was identified as the best month for planting, as it exhibited the lowest disease incidence along with superior growth and yield characteristics compared to other planting months. On the other hand, planting during the winter season (September to January) resulted in high disease severity due to an increased aphid population. Conversely, planting during the low aphid population period (spring season) delayed disease incidence until the monsoon. By the time the aphid population starts to increase, the plants have already passed the flowering and fruit-bearing stages. In the second experiment, the severity and frequency of foliar symptoms on PRSV-inoculated papaya plants were significantly higher in plants inoculated at the early growth stage compared to those inoculated at a later growth stage. This suggests that the early crop growth stage (up to 180 days after transplanting) is a critical period for PRSV infection, and effective disease management measures should be implemented during this time to control the spread of the disease and improve growth and yield parameters. Additionally, plants inoculated at an early stage had a higher viral titer, more severe symptoms, and a higher percent transmission rate compared to those inoculated at a later stage, demonstrating a highly significant and positive correlation using qRT-PCR.