Awn Reduction and the Domestication of Asian Rice: A Syndrome or Crop Improvement Trait?

Abstract

Awn Reduction and the Domestication of Asian Rice: A Syndrome or Crop Improvement Trait? Although wild progenitors of Asian cultivated rice have long awns, they are shorter or absent in domesticated landraces and cultivars. Thus, one may wonder when and why such transition from awned to awnless has occurred, i.e., is the reduction of awns a domestication syndrome trait or a trait that emerged during crop improvement? The proponents of an evolutionary model of rice domestication consider the loss/reduction of seed dispersal aids as a key domestication syndrome trait, apart from the fixation of seed retention. We challenge this view by showing that early cultivators had incentives for selecting long awns before and even after the fixation of the non-shattering trait. This is because long awns prevented seed predation by animals and facilitated harvest by means of the basket-beating method, which implies that their presence improved yield and labor efficiency. Our arguments also reveal that awns perhaps have persisted long after domestication and even after the introduction of sickles. Taken together, the reduction of awns may not fit into a domestication syndrome trait, but it can most plausibly be considered as a crop improvement trait.