Abstract

Papaya ringspot disease is a serious threat to papaya production in Kenya. For effective management, it is important to determine the occurrence and distribution of the viruses associated with the disease. A survey was conducted in 2017, covering a total of 103 papaya fields in major papaya production areas in the country. To determine the disease incidence, 20 plants per field were visually inspected for symptoms associated with the disease. Disease severity was evaluated on a scale of 1 to 5, while disease prevalence was determined as the proportion of fields showing disease symptoms per county expressed as a percentage. A total of 287 leaf samples were collected from surveyed fields and tested for Moroccan watermelon mosaic virus (MWMV), cowpea mild mottle virus (CpMMV), and papaya mottle-associated virus (PaMV) using polymerase chain reaction (PCR)-based techniques. The highest (71.4%) disease incidence was recorded in Kiambu County, while the lowest was recorded in Busia County (2.8%). No symptomatic plants were observed in Siaya and Bungoma (0%) counties. Disease prevalence ranged from 0 to 100%. The highest disease severity, 4.0, was reported in Baringo County; while the lowest, 2.0, was reported in Kwale, Kilifi, and Taita Taveta counties. MWMV was the most prevalent, with 140 out of 287 samples testing positive and also widespread, having been detected in 11 out of the 22 counties surveyed. PaMV was the second most prevalent, detected in 39 out of 287 samples collected and in 9 out of 22 counties. CpMMV was the least prevalent, detected in 7 out of 287 samples and in three counties. The occurrence of both MWMV and PaMV was detected in five counties, while the occurrence of PaMV and CpMMV was detected in three counties. The presence of MWMV, PaMV and CpMMV was detected in one county. Viruses associated with papaya ringspot disease in Kenya are widespread in papaya-growing regions, with some counties reporting 100% disease prevalence. The development and implementation of control strategies for the disease in the country are of paramount importance. In the future, it is important to identify factors influencing disease spread in the country for effective management.

Key words: Incidence, viral diseases, control strategies, farmers, interventions.