Genetic architecture and cellular basis of flag leaf size in barley

The flag leaf is a major contributor of photosynthetic assimilates to developing grains. We investigated the genetic architecture and cellular basis of flag leaf length (FLL) and width (FLW) in a multiparent population of 45 recombinant inbred line (RIL) populations (HvDRR) in barley. Fine-mapping of a major quantitative trait locus (QTL) was performed to prepare the isolation of the causal gene. Natural variation of FLL and FLW across environments was highly heritable, and genotypes from warm climates produced longer and wider flag leaves than those from cooler regions. Variation in flag leaf size was quantitatively inherited and influenced by 24 consensus QTLs, of which 17 have not previously been reported. Validation of QTLs qHvDRR-FLS-8 and qHvDRR-FLS-17 in nearly isogenic RILs showed that these QTLs also controlled length and width of leaves older than the flag leaf. The number of epidermal cells primarily determined FLL, whereas the number and size of epidermal cells collectively determined FLW differences. In addition, we identified the previously unknown effect of genic alleles and epialleles at Vrn-H1 on flag leaf size variation in spring barley. Furthermore, we fine-mapped qHvDRR-FLS-8, narrowing the interval from 8.7 Mb to 3.5 Mb. In conclusion, our study identified the genomic regions associated with morphological and anatomical variation for leaf size and set the stage to uncover causal genes.