Monoculture and Polyculture: Why Food Crops Need Variety

0:00Why grow many kinds of crops, instead of only the one with the biggest harvest?

0:06A monoculture is a field of just one crop, usually one variety. It is efficient to farm.

0:13Its plants are genetically alike. Bananas and potatoes are even clones: copies with identical genes, grown from pieces of one parent.

0:23A polyculture mixes several crops or varieties, so its plants have genetic variation: different genes.

0:31Now a pathogen arrives: a living thing that causes disease, such as a fungus.

0:37In the monoculture, no plant has resistance, an inherited ability to fight the disease, so it spreads to every plant.

0:46In the polyculture, only plants without resistance die. Resistant plants survive and pass on their genes: natural selection.

0:56This really happened: by the 1960s, a fungus had wiped out the cloned Gros Michel banana on export farms.

1:05In the 1840s, potato blight swept through fields of genetically similar potatoes and caused a famine.

1:12These crops come from artificial selection: people breed the plants that give the most food, the highest yield.

1:21But the highest yield crop is not always the safest choice: one disease can destroy all of it.

1:28Polyculture spreads the risk, supports more species, and keeps soil healthier.

1:35Seed banks store seeds of many varieties, so breeders can find resistance genes for new diseases.

1:42Variety spreads the risk, so one disease is far less likely to destroy the whole harvest.