24Cassava is one of the most important annual crops in Southeast Asia, and faces increasing seed borne 25 pest and disease pressures. Despite this, cassava seed systems have received scant research attention. 26In a first analysis of Vietnamese and Cambodian cassava seed systems, we characterized existing 27 cassava seed systems in 2016-17 through a farmer survey based approach at both national and 28 community scales, with particular focus on identifying seed system actors, planting material 29 management, exchange mechanisms, geographies, and variety use, and performed a network analysis 30 of detected seed movement at the provincial level. Cassava seed -Vietnam and Cambodia 2 commercial sale was more prevalent in high-intensity than in low-intensity production sites. 44Considerable variability existed in local seed networks, depending on the intensity of production and 45 integration with trader networks. Adapted innovations are needed to upgrade cassava seed systems in 46 the face of emerging pests and diseases, taking into account and building on the strengths of the 47 existing systems; including their social nature and ability to quickly and efficiently distribute planting 48 materials at the regional level. 49

24Cassava is one of the most important annual crops in Southeast Asia, and faces increasing seed borne 25 pest and disease pressures. Despite this, cassava seed systems have received scant research attention. 26In a first analysis of Vietnamese and Cambodian cassava seed systems, we characterized existing 27 cassava seed systems in 2016-17 through a farmer survey based approach at both national and 28 community scales, with particular focus on identifying seed system actors, planting material 29 management, exchange mechanisms, geographies, and variety use, and performed a network analysis 30 of detected seed movement at the provincial level. Cassava seed -Vietnam and Cambodia 2 commercial sale was more prevalent in high-intensity than in low-intensity production sites. 44Considerable variability existed in local seed networks, depending on the intensity of production and 45 integration with trader networks. Adapted innovations are needed to upgrade cassava seed systems in 46 the face of emerging pests and diseases, taking into account and building on the strengths of the 47 existing systems; including their social nature and ability to quickly and efficiently distribute planting 48 materials at the regional level. 49