Variety and on-farm seed management practices affect potato seed degeneration in the tropical highlands of Ecuador

Studies in the Andes have demonstrated that seed degeneration of potato occurred in experimental conditions, but was negligible in farmers' conditions. There are two hypotheses for this difference: (1) farmers cultivate resistant varieties, or (2) they use on-farm practices that can manage seed degeneration. Farmers may replace some of the seed saved from their fields with outside seed, but it is an open question what level of benefit farmers experience from partial replacement. The objective of this study was to investigate the role of the cultivated varieties, the on-farm seed management practices, and seed replacement in potato seed degeneration. Moreover, this study evaluated the potential effect of partial replacement of the farmers' seed lot each season with healthy seed, compared to less frequent nearly full replacement, in simulations. We surveyed farmers in the Cotopaxi province, Ecuador, in 2008, 2010, and 2018, and performed a study on the incidence of pathogens and pests in farmers' seed lots in 2018. We also evaluated the potential effects of the timing of replacement of farmers' seed lots by healthy seed to manage degeneration, applying the seedHealth model. We found that farmers experience no or only slow degeneration in their varieties. Analysing yield data reported by farmers to detect degeneration, we did not detect yield declines. The type of variety and year of data collection explained the variation in yield. These results seem to confirm the hypothesis that varieties cultivated in the Andes are resistant to the impact of seed degeneration on yield, and that seed degeneration depends on the agroecological conditions present within a cropping season or year. Because we did not find an impact on yield, we hypothesized that on-farm practices affect seed-borne pathogens and pests causing seed degeneration. We identified multiple on-farm practices playing a role in the process of seed degeneration: they either slowed down or accelerated this process depending on the seed-borne pathogen and pest causing seed degeneration. Our scenario analyses using the seedHealth model showed how replacing farmers' seed lots by healthy seed could usefully reduce seed degeneration compared to using the same amount of seed to periodically replace nearly all seed in a season. Our results showed that on-farm practices are also critical drivers in the process of seed degeneration. This study demonstrated the importance of considering on-farm seed management prac