Farm Radio International recommends to collect seed including tubers and cuttings. They offer insight on how to accomplish this task effectively by stating "seed bank workers organize seed collection carefully. The group should approach farmers for some of their extra seed. Remember that farmers must first collect enough seed for their own use. Never take seed from farmers without permission. Collect whatever seed the farmers can spare, at least in the first year. After a year's experience you will know what the seed bank workers can manage."
Some plants grow from tubers or cuttings. Collect these as well. Farmers will know when is the best time of year is to collect seed, tubers, and cuttings. As you collect seed, Farm Radio International says to:
"a. Save seeds from useful crops and wild plants which people in the community think are important, and from those plants which you know are only grown locally. Farmers will tell you how much seed they can spare for each crop or plant.
b. If the land is no longer productive because of soil erosion, drought, or deforestation, you should save seeds from wild plants, and even from weeds. Often these plants are related to other plants which farmers find useful. For example, modern potatoes, tomatoes, and squash have relatives which grow wild. If the land is still productive, you may not need to collect seeds from wild plants, but you should always protect wild plants from overgrazing and soil erosion.
c. Collect a wide variety of seed from every type of crop by walking through the field and randomly picking seed from the plants, or from several different fruits. If the plants have different characteristics such as good fruit, drought tolerance, or resistance to insects, you will need to collect more seed. Always try to collect as much as possible.
d. Save seeds from the best and worst looking plants. Collect seeds from both strong and weak plants. Also, save seeds from plants which don't look normal. These plants may offer something important which you cannot easily see, such as tolerance to poor soil, drought, insects, strong sunlight or shade. If the plant is diseased, you should also collect seeds only if the fruit is still healthy. Many plants can tolerate disease or pests, and still produce high yields. Collect and store seeds from diseased plants in a separate container so that the disease will not spread. Keep them in reserve just in case your healthy plants don't grow. Do not plant seeds from unhealthy plants unless no healthy seeds will grow because insects can carry disease from sick plants to healthy plants. Never grow them together.
e. Save seed from plants even if they have invaded or have been introduced into the area in recent years. Some plants change, adapt, and sometimes improve, in new growing conditions within only a few seasons."
Source: Farm Radio International, "Starting a Community Seed Bank," Package 33, Script 4, July 1994.