Abstract Description

In South Africa, smallholder and emerging farmers grow leafy vegetables such as Swiss chard, mustard spinach and beet greens for household consumption and income generation. Viral diseases pose a significant threat to production. Viruses belonging to the Luteoviridae and Potyviridae were reported globally to infect these vegetables. However, their impact in South Africa is poorly understood. The study was aimed at identifying and genetically characterizing viruses affecting leafy vegetables production in Gauteng Province. Samples were collected in 3 regions of Gauteng (City of Tshwane, Randfontein and Germiston) using a W-pattern method of sampling. Symptoms were evaluated visually using a score scale of 0-5, where 0 represented no symptoms and 5 very severe symptoms. Data was subjected to statistical analysis using SAS statistical software and combined analysis of variance (ANOVA) was conducted. Significant effects were compared using Fisher’s unprotected t-least significant difference (LSD) at a 5% level of significance. Samples were tested using Transmission Electron Microscope (TEM) imaging and reverse transcription polymerase chain reaction (RT-PCR). Next-generation sequencing (NGS) was used to generate complete genome sequences of viruses detected. The prevalence of virus symptoms ranged from 75% (Winterveldt) to 83% (Majaneng) in Tshwane. TEM revealed filamentous viral particles associated with potyviruses. Commonly detected viruses included Turnip mosaic virus (TuMV), Beet mosaic virus (BtMV), Beet western yellows virus (BWYV) and Beet chlorosis virus (BChV). DNA sequencing confirmed the findings and identified a virus named Brassica napus RNA virus 1 (BnRV1). This study is the first to report BnRV1, BtMV, BWYV and BChV in South Africa affecting Swiss chard, mustard spinach and beet greens. These findings will contribute to the development and implementation of control strategies, crucial for sustainable leafy vegetable production in the country. There are viruses never detected previously on leafy green vegetables in South Africa. These viruses cause damage and yield loss and need to be included in monitoring and control strategies.