Rice yellow mottle virus (RYMV) is the most important rice virus in Africa. We examined RYMV transmission via soil and water contaminated with RYMV-infected rice plants and by serial cutting with RYMV-contaminated scissors. Transmission of RYMV via dried rice straw kept at 27°C was also examined. The results showed the virus could be transmitted via soil and water, and by scissors. Rice straw that was RYMV-infected was not infective if it was dried and was kept longer than 42 days. By insect transmission experiments and ELISA, long-horned grasshoppers (Conocephalus spp.) were found to be a possible vector of RYMV in Uganda.

The Kilombero Valley, one of East Africa’s largest seasonal wetlands, is a high-potential agricultural development corridor area in Tanzania. This seasonally flooded wetland is mainly used by smallholder farmers who cultivate during the rainy season, although there are some community-based irrigation systems that reduce hydro-climatic risks. In this study, we aim to understand how farmers’ aspirations and visions about the future are related to the current agricultural practices and human–water interaction. We specifically investigate the differences between farmers from rainfed and irrigated agriculture by using focus group discussions. Analysis of the in-depth interviews highlights how farmers’ actions both shape and respond to this highly dynamic and uncertain environment. Furthermore, we identify a close link, driven by the farmers’ level of agency, between aspirations and expected agro-economic development. The heterogeneity of farmers’ agency and hence their ability to cope with change is not only based on the socioeconomic status but also on their perception of the physical environment. We thus recommend that attention is also paid to the capacity for coping with environmental challenges that influences the level of farmers’ aspiration.

Rice yellow mottle virus (RYMV) causes severe rice (Oryza sativa L.) yield loss. It has been endemic to sub-Saharan Africa and Madagascar since 1966. Transmission (plant community level) and long-dispersal (regional and continental scale) models have been established but viral spread in farming communities continues, while the conditions causing local disease outbreaks remain unclear. We hypothesized that local outbreaks, comprising inter-plot virus spread and intra-plot disease aggravation, are significantly associated with individual farmers’ attributes and agronomic practices. To test this hypothesis, spatial autoregressive models were constructed using variables collected by visual observation and farmer interviews. Field surveys were conducted during four consecutive cropping seasons from 2011 to 2013 in the Lower Moshi Irrigation Scheme of Kilimanjaro, Tanzania. Our models detected spatial dependence in inter-plot virus spread, but not in intra-plot disease aggravation. The probability of inter-plot virus spread increased with use of the IR64 cultivar (26.9%), but decreased with straw removal (27.8%) and crop rotation (47.7%). The probability of intra-plot disease aggravation decreased with herbicide application (24.3%) and crop rotation (35.4%). A simple cost-benefit analysis suggested that inter-plot virus spread should be mitigated by cultivar replacement and straw removal. When disease severity is critical, intra-plot disease aggravation should be inhibited by herbicide application, and rice should be rotated with other crops. This is the first study to upscale the spatial autoregressive model from the experimental field level to the farming community level, by obtaining variables through easy-to-implement techniques such as visual observation and farmer interview. Our models successfully identified candidate agronomic practices for the control of RYMV. However, as the causal relationships between agronomic practices and RYMV outbreaks remain unknown, field trials are needed to develop robust control measures.

<p>At present, the seasonally flooded wetland of the Kilombero River is mainly used by small-scale farmers who predominantly produce rice and maize during the wet season. Some community-based irrigation systems do exist, which reduce the consequences and risks of climate variabilities regarding e.g. the onset of the rainy season and which allow year-round farming. Like other sub-Saharan wetlands, the Kilombero Valley floodplain is a highly dynamic environment, which is amplified due to increasing variability in the onset and intensity of the wet season.</p><p>In this study, we identify drivers of change and farmers’ decision-making strategies using focus group discussions with different types of farmers. In particular, we examine the differences between farmers from rain-fed and irrigated agriculture in terms of their agricultural practices and decision-making strategies for dealing with hydro-climatic risks. The results map the perceptions and visions of the people whose actions shape this highly dynamic environment and identify a range of options for action that go beyond the optimality paradigm.</p><p>Understanding how aspirations and visions about the future shape agricultural practices and hence human-water interaction is crucial to understand possible changes and dynamics of coupled socio-ecological systems. Therefore, this study is embedded into a wider multi-method approach integrating qualitative and quantitative data to inform and modify hydrological modelling. Here, the qualitatively collected data and findings of this research provide ground for developing additional scenarios for hydrological models and allow for contextualizing model results. Thus, human-water interactions can be better represented and the local populations’ perception and reactions to hydro-climatic risks can be assessed.</p><p>This research is part of the Collaborative Research Centre 228 “Rural Future Africa” funded by the German Research Foundation (DFG).</p>