Seed degeneration of potato in the tropical highlands of Ecuador

Navarrete, Israel


Potato seed degeneration is considered an important seed and yield limiting problem for farmers in Ecuador and other low-income countries. This problem is defined as the process of accumulation of pathogens and pests in/on the seed that occurs when farmers propagate their seed tubers (hereafter seeds) on-farm for successive cycles. The main causes of seed degeneration in Ecuador are Rhizoctonia (Rhizoctonia solani), the Andean weevil (Premnotrypes vorax), Potato virus X, Potato virus S, and purple top disease. The process of seed degeneration could be interacting with different conditions and factors under the farmers’ context such as farmers’ socioeconomic conditions, agroecological conditions, on-farm management practices, and potato varieties. This thesis aims to shed light on these interactions using information collected in the tropical highlands of Ecuador.

This thesis began by focusing on purple top, a disease that is spreading in the potato production areas of Ecuador since 2012-2013. A literature review and an innovation history analysis were performed to identify lessons to manage purple top disease. The results showed that stakeholders implemented different initiatives to identify or confirm the causal agent(s), raise funding for research and communication, raise awareness and design management strategies. However, a better coordination and political lobby are necessary to manage this problem. Results showed that it is necessary to strengthen the coordination and communication between stakeholders, the design and implementation of interventions, the acquisition of funding, policies and regulations, and research and surveillance.

Subsequently, this thesis focused on how seed degeneration occurs in experiments and farmers’ fields under different agroecological conditions. For this objective, I analysed the information collected during a multi-annual experiment and farmers’ seed surveys. The results showed that agroecological conditions influenced the presence of pathogens and pests causing seed degeneration. Results showed that agroecological conditions and the cycles of on-farm propagation influence the process of seed degeneration under experimental conditions, but not under farmers’ conditions. Results suggest that potato seed degeneration is not the main yield limiting factor under farmers’ conditions in the tropical highlands of Ecuador.

Based on the previous findings, this thesis investigated the role of varieties, seed replacement and other local on-farm seed management practices in seed degeneration. The data of three independent farmers’ surveys and a farmers’ seed study are analysed. Results showed that there were 65 potato varieties and 36 on-farm management practices used or implemented by farmers. Results indicated that the type of variety (improved or native varieties) and the farmers’ practices are influencing the process of potato seed degeneration. The seedHealth model was used to understand if replacing part of the farmers’ seed by different percentages of healthy seed at different frequencies could help to manage degeneration under low and high external inoculum conditions. The results suggested that replacing part of farmers’ seed could be a promising practice to manage seed degeneration.

Next, this thesis focused on understanding the role of farmers’ experience on seed degeneration and their responses. The information from focus groups discussions, farmers’ surveys, and interviews was analysed. Information of the income data of the Ecuadorian employment status survey was also used. Results showed that not all farmers experienced seed degeneration. However, farmers who experienced seed degeneration used different indicators to identify this problem such as low yield, change in physical appearance, crop weakening and seed physiological problems. The results showed that farmers replaced their seed, sought for technical advice, increased the use of agricultural inputs, and replaced the crop when the seed was degenerated. Yet, the results suggest that seed replacement practices do not change because of farmers’ experience on seed degeneration, but because of their income.

This thesis shows there are multiple interactions between potato seed degeneration and farmers’ socioeconomic conditions, agroecological conditions, farmers’ management practices, and potato varieties under farmers’ conditions in the tropical highlands of Ecuador.