Grain Disarticulation in Wild Wheat and Barley

Abstract

Our industrial-scale crop monocultures, which are necessary to provide grain for large-scale food and feed production, are highly vulnerable to biotic and abiotic stresses. Crop wild relatives have adapted to harsh environmental conditions over millennia; thus, they are an important source of genetic variation and crop diversification. Despite several examples where significant yield increases have been achieved through the introgression of genomic regions from wild relatives, more detailed understanding of the differences between wild and cultivated species for favorable and unfavorable traits is still required to harness these valuable resources. Recently, as an alternative to the introgression of beneficial alleles from the wild into domesticated species, a radical suggestion is to domesticate wild relatives to generate new crops. A first and critical step for the domestication of cereal wild relatives would be to prevent grain disarticulation from the inflorescence at maturity. Discovering the molecular mechanisms and understanding the network of interactions behind grain retention/disarticulation would enable the implementation of approaches to select for this character in targeted species. Brittle rachis 1 and Brittle rachis 2 are major genes responsible for grain disarticulation in the wild progenitors of wheat and barley that were the target of mutations during domestication. These two genes are only found in the Triticeae tribe and are hypothesized to have evolve by a duplication followed by neo-functionalization. Current knowledge gaps are the molecular mechanisms controlling grain retention in cereals and the genomic consequences of strong selection for this essential character.

Phenotyping and identification of target traits for de novo domestication of wheat wild relatives

“…This trait is mainly influenced by the Brittle rachis 1 and Brittle rachis 2 ( Btr ) genes on chromosome 3. Their loss of function enables the non‐shattering phenotype (Pourkheirandish & Komatsuda, 2022). Thus, those genes should be the first target for de novo domestication of wild wheats.…”

Form follows function in Triticeae inflorescences

“…Grain shattering has long been recognized to cause yield losses in cereal crops ( Bolland 1984 , Clarke 1981 , Sugimoto et al 2010 ). Grain shattering is distinguished from the brittle rachis trait shown in wild barley and wild emmer wheat ( Pourkheirandish and Komatsuda 2022 ), with the causal loss-of-function mutations located at Non-brittle rachis 1 ( btr1 ) and btr2 ( Avni et al 2017 , Pourkheirandish et al 2015 ). In grain shattering, spikelet disarticulation from rachis occurs above the glume whereas in brittle rachis phenotype, disarticulation occurs below the glume ( Sakuma et al 2011 ).…”