Climate-related risk modeling of Banana Xanthomonas Wilt (BXW) disease incidence within cropland area of Rwanda

Banana Xanthomonas Wilt (BXW) is the major threat to banana in Rwanda, causing up to 100% yield loss. There are no biological or chemical control measures, and little is known about potential direction and magnitude of its spread, so cultural control efforts are reactive rather than proactive. In this study, we assessed BXW risk under current and projected climate, to guide early warning and control by applying maximum entropy (Maxent) model on 1,022 georeferenced BXW datapoints and 20 environmental variables. We evaluated the variables' significance and mapped potential risk under current and future climates to assess spatial dynamics of the disease distribution. BXW occurrence was reliably predicted (mean validation AUC ranging from 0.79 - 0.85). Precipitation of the coldest quarter, average maximum monthly temperature, annual precipitation, and elevation were strongest predictors, explaining 21.1%, 13%, 12.6%, and 9.4% of the observed incidence variability, respectively, while mean temperature of the coldest quarter has the highest gain in isolation. Further, the most susceptible regions (in western, northern, and southern Rwanda) are characterized by elevation (1,350m - 2,000m), annual precipitation (900mm - 1700mm), and average temperature (14oC - 20oC), among other variables, suggesting that a consistent, rainy, and warm climate is more favorable for BXW spread. Under future climate, the risk is predicted to increase and spread to other regions. We conclude that climate change will likely exacerbate BXW-related losses of banana land area and yield, under temperature and precipitation influence. Findings support evidence-based targeting of extension delivery to farmers and national early warning for timely action.

Evaluation Of Mycotoxin Content In Soybean (Glycine max L.) Grown In Rwanda

Soybean is a critical food and nutritional security crop in Rwanda. Promoted by the Rwandan National Agricultural Research System for both adults and as an infant weaning food, soybean is grown by approximately 40% of households. Soybean may be susceptible to the growth of mycotoxin-producing moulds; however, data has been contradictory. Mycotoxin contamination is a food and feed safety issue for grains and other field crops. This study aimed to determine the extent of mycotoxin contamination in soybean, and to assess people's awareness on mycotoxins. A farm-level survey was conducted in 2015 within three agro-ecological zones of Rwanda suitable for soybean production. Soybean samples were collected from farmers (n=300) who also completed questionnaires about pre-and post-harvest farm practices, and aflatoxin awareness. The concentration of total aflatoxin in individual soybean samples was tested by enzymelinked immunosorbent assay (ELISA) using a commercially-available kit. Other mycotoxins were analyzed using liquid chromatography-mass spectrometry (LCMS/MS) on 10 selected sub samples. Only 7.3% of the respondents were aware of aflatoxin contamination in foods, but farmers observed good postharvest practices including harvesting the crop when the pods were dry. Using enzyme-linked immunosorbent assay (ELISA), only one sample had a concentration (11 µg/kg) above the most stringent EU maximum permitted limit of 4 µg/kg. Multi-mycotoxins liquid chromatography-mass spectrometry (LC-MS/MS) results confirmed that soybeans had low or undetectable contamination; only one sample contained 13µg/kg of sterigmatocystine. The soybean samples from Rwanda obtained acceptably low mycotoxin levels. Taken together with other studies that showed that soybean is less contaminated by mycotoxins, these results demonstrate that soybean can be promoted as a nutritious and safe food. However, there is a general need for educating farmers on mycotoxin contamination in food and feed to ensure better standards are adhered to safeguard the health of the consumers regarding these fungal secondary metabolites.