Agricultural scientists have long concluded that the seed of some crops degenerates steadily with each planting. This is especially true for crops that are planted vegetatively, for example through cuttings or tubers, like the potato. Degeneration is the buildup of pests and diseases, passed one from one generation to the next in vegetative seed, slowly lowering the crop’s yield.
A long-term study by Ecuadorian plant scientist, Israel Navarrete, was able to reconfirm this, but only in experiments, not in farmers’ fields. In experimental plots at different altitudes in the high Andes, potatoes originally planted from certified (healthy) seed acquired more viruses and other pathogens every year, for three years.
However, Navarrete found no evidence of seed degeneration on Ecuadorian farms. He surveyed 260 households, to collect information on how they grew potatoes. A typical survey stops there, but Navarrete also collected a seed sample from each family. Later, in the laboratory, he diagnosed these seed potatoes for pests and diseases.
Counter to conventional wisdom, Navarrete found that farmers’ seed was not degenerating. Potatoes grown on the same farm for over ten years were as healthy as those cultivated only recently. The reason, Navarrete explains, is that farmers have their own methods for keeping seed healthy. For example, farmers in Ecuador often select seed, searching through the piles of tubers, picking out the best ones. They also store seed until it sprouts, which seems to improve its health. Other farmers stored seed in bags or applied fertilizer. From his survey, some 36 local practices were identified that influenced seed health.
The farmers themselves knew they were doing something right. Only 16%, said that degeneration was a problem for them, although they were aware of it. When seed degenerates, Ecuadorian farmers say that it has become “tired.” Then they replace it.
Of course, not all local habits make for healthy seed. When potato prices soar, farmers are often tempted to sell as much as possible, even some of the tubers that would make good seed.
Navarrete encourages other agricultural scientists to learn about seed health from farmers. Later, scientists can recommend helpful new ideas to the farm families. Navarrete and colleagues have a few such suggestions, such as encouraging farmers to grow a small, special field as a seed lot, where the healthiest plants can be saved as the mothers of next year’s seed.
This study shows the limits of the experimental method, which looks at one variable at a time. The real world of farming is messy. Seed may degenerate in a carefully controlled experiment, but not so much in the field, because farmers manage it. Researchers may be keen to show how seed degenerates, while farmers are working to avoid it.
Further reading
Navarrete, Israel 2021 Seed Degeneration of Potato in the Tropical Highlands of Ecuador. Ph.D. thesis. Wageningen University, The Netherlands. 234 pp.
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