Abstract
Abstract Potato seed systems in Kenya are largely informal, characterized by high seed degeneration due to the buildup of seed- and soil-borne diseases, including bacterial wilt caused by Ralstonia solanacearum . Informal sources of seed include neighbors, local markets and farmer-saved seed, and present a risk for spread and establishment of disease. To understand the larger context of potato disease risk in Kenya, we used network analysis to evaluate (1) epidemic risk through potato trade networks centered around East Africa, and (2) locations in East Africa likely to be particularly important for epidemic management because of their high potato cropland connectivity. We evaluated the interactions of the key stakeholders in a potato seed system and used network analysis to identify locations that are likely to be important for the spread of infection of R. solanacearum in a potato seed distribution network in Meru, Kenya. Household details, seed sources, quantities sold, pest incidence and management practices, knowledge about seed degeneration and farmers' sources of information on potato production were obtained and analyzed. The survey revealed that self-saved, neighbors, seed companies, friends, exchange, and markets are the main seed sources. Only 43% of total seed transacted was certified. Users of uncertified seeds have high disease risk, and this is an especially important risk if their roles in the network give them the potential to be 'superspreaders' of disease.
Highlights
Potato is an important food security crop and a major source of household income for smallholder farmers in Kenya (MOALF, 2016)
We evaluated the connectivity of the potato cropland network using a cropland connectivity risk index (CCRI) (Xing et al, 2020) in Sub-Saharan Africa, using the harvested potato area data in SPAM 2017 v2.1 (International Food Policy Research, 2020) by converting grid harvested area values in hectare as grid fraction of harvested area, with a 5 x 5 minute grid unit of cropland as a geographic node and the probability of pathogen spread between pairs of nodes as link weights
Cropland connectivity analysis and trade network structure, The uncertainty quantification analysis of the CCRI for potato production in Sub-Saharan Africa indicates locations that are likely to be important in epidemics, in terms of the potential for pathogen spread through the landscape (Fig. 1)
Summary
Potato is an important food security crop and a major source of household income for smallholder farmers in Kenya (MOALF, 2016). The crop grows well between 1500 masl and 3000 masl; Meru, Nakuru, and Nyandarua are the main potato producing counties in Kenya, accounting for 80% of the total potato production (Kaguongo et al, 2014; 2010; Muthoni et al, 2013; Were et al, 2013). The low productivity is mainly attributed to the erratic rainfall patterns, lack of high yielding varieties, unavailability of and limited access to certified seed potatoes, and pest and diseases such as late blight (caused by Phytophthora infestans), bacterial wilt (caused by Ralstonia solanacearum) and viruses (Potato virus X, Potato virus Y and Potato leafroll virus) (Gildemacher et al, 2009; Kaguongo et al, 2014). Lack of adequate certified potato seed has increased the seed and soil borne disease problem in Kenya (Muthoni et al, 2013)
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