Crops made, and remade

Two new studies of very different crops – banana and chrysanthemum, of all things – end up telling surprisingly similar, deliciously complicated stories. For these crops, domestication was not once and done, so to speak. They were both repeatedly remade as people moved them through landscapes containing new wild diversity.

In the banana study, the authors suggest that a partly domesticated Musa acuminata lineage from New Guinea was carried westwards through Southeast Asia, encountering and hybridizing again and again with different local wild bananas along the way. Each encounter added new genetic material to an already changing crop, helping produce the genomic mosaics found in mainland Southeast Asian bananas today.

The chrysanthemum study reveals a strikingly parallel history: cultivated plants originating in China were introduced to Japan, where they encountered local wild populations and acquired new genetic diversity, before later movements to Europe and further breeding reshaped the crop again.

The studies also document how an essentially similar process played out somewhat differently in the two crops. In banana, repeated hybridization appears to have been important in the building of the crop itself, as domesticated or partly domesticated plants became the starting material for successive encounters with wild Musa. In chrysanthemum, genomic analysis reveals a more complex network of relationships among multiple wild and cultivated groups, with C. indicum among the important ancestral contributors. In this genetic cauldron, hybridization and introgression repeatedly diversified an established cultivated genepool, contributing to traits such as flower form, colour and plant architecture.

Taken together, these papers challenge the familiar “funnel,” or bottleneck, image of domestication: a one-way downward slide from diverse wild relative to genetically narrow crop. Instead, they point to a more stop-start, two-way, non-linear, geographically contingent process, in which (semi-)cultivated plants continue to encounter, absorb and be reshaped by wild diversity.

In both banana and chrysanthemum — and probably many other cases — wild relatives have been more active, continuous participants in creating the diversity of the crops we know today than we sometimes give them credit for. Or I have given them credit for at any rate.

That argues for treating the wild genepool not simply as a reservoir from which to fish out useful genes one at a time. The historical evidence suggests that crops have benefited in the past from repeatedly absorbing larger chunks of wild genetic diversity, allowing selection to reconstruct useful combinations. Might it be worth trying to make that happen again? Is anyone out there doing pre-breeding explicitly with an eye to the past?