Since mid-1980s, plant geminiviruses transmitted by Bemisia tabaci became major causes of yield reduction in vegetables, especially in tomato. They induce symptoms of leaf curling and yellowing and sometimes stunting of infected plants. This obliged many farmers to abandon tomato in favor of other crops such as onions. Preliminary data indicated the occurrence of a complex of at least five viral species. These results suggested a hidden diversity of Geminiviruses and indicated that tomato is subject to multiple infections. However, the epidemiology of induced diseases remains poorly understood which hampers the design of appropriate control measures that could be used by farmers to reduce yield losses. This project aimed at identifying the key epidemiological aspects of diseases caused by geminiviruses in tomato. More precisely, the specific objectives were to (1) make an exhaustive list of plants reservoirs of tomato infecting geminiviruses, (2) follow the evolution of the virus populations on tomato, (3) estimate crop losses caused by different diseases and (4) identifying accessions of tomato susceptible to be resistant/tolerant to geminivirus infections. To achieve these objectives:
- Surveys and sample collections were carried out during hot dry, wet and cold dry seasons in the humid Sudan and sub-humid Sudan-Sahel areas where geminivirus diseases were endemic. Leaf samples were collected form tomato and uncultivated plants during two consecutive years.
- Detection of geminiviruses was conducted using collected samples to access geminivirus diversity and their reservoirs based on molecular tools
- Screening of farmer’s preferred tomato accessions was carried out using tomato local accessions. The main epidemiological parameters were the plant height and symptom notation to access disease incidence and prevalence, fruit weight at harvest to access impact of diseases on yield and the detection of geminivirus by PCR to access geminivirus incidence.

Plants reservoirs of tomato infecting geminivirus in Burkina Faso
Based on PCR assay and nanopore MinION sequencing assay, this study confirms the presence of geminiviruses on tomato plants and several cultivated and uncultivated plants bordering tomato fields. These plants include medicinal weeds (Ouattara et al. in preparation). In this study, Tobacco plants were reported, for the first time, to be naturally infected by the Pepper yellow vein Mali virus, an aggressive virus with wide
distribution in Burkina Faso with typical symptoms (Ouattara et al., 2023a).

Evolution of the virus populations on tomato in Burkina Faso
Base on molecular diagnosis tools, our results highlight the presence of Tomato leaf curl Mali virus and PepYVMLV as the most prevalent viruses on tomato in Burkina Faso.

Screening of widely used accessions of tomato for resistance/tolerance to geminiviruses
To estimate crop losses caused by virus diseases and to identify resistant/tolerant accessions of tomato, an inventory of tomato accessions sold and produced in Burkina Faso were conducted. This showed sixteen varieties sold in shops, with Mongal F1, Emerald F1, and Cobra 26 F1 reported to be the most preferred by farmers. Monitoring of most preferred tomato accession plants inoculated with the virus, during 32 days, showed that Diva F1, a newly introduced accession, was the least susceptible to PepYVMLV, followed by the three preferred accessions, with yield losses ranging from 25.38 to 359.9 g/plant. Our results suggest that even if the productivity of Diva F1 seems to be slightly impacted by the virus, it is unsuitable for farmers because of its lower yield (Ouattara et al., 2023b)

TWAS