Hop (Humulus lupulus L.) inflorescences, commonly known as "hop cones", are prized for their terpenophenolic contents, used in beer production and, more recently, in biomedical applications. In this study we investigated morphological and phytochemical characteristics of hop cones over five developmental stages, using liquid chromatography coupled to time-of-flight mass spectrometry (LC-TOF-MS), and ultrahigh performance liquid chromatography photodiode array detection (UHPLC-PDA) methods to quantitate 21 polyphenolics and seven terpenophenolics. Additionally, we used light microscopy to correlate phytochemical quantities with changes in the morphology of the cones. Significant increases in terpenophenolics, concomitant with glandular trichome development and associated gross morphological changes, were mapped over development to fluctuations in contents of polyphenolic constituents and their metabolic precursor compounds. The methods reported here can be used for targeted metabolic profiling of flavonoids, phenolic acids, and terpenophenolics in hops, and are applicable to quantitation in other crops.

Hop (Humulus lupulus L.) breeding programs seek to exploit genetic resources for bitter flavor, aroma, and disease resistance. However, these efforts have been thwarted by segregation distortion including female-biased sex ratios. To better understand the transmission genetics of hop, we genotyped 4512 worldwide accessions of hop, including cultivars, landraces, and over 100 wild accessions using a genotyping-by-sequencing (GBS) approach. From the resulting ~1.2 million single-nucleotide polymorphisms (SNPs), prequalified GBS markers were validated by inferences in population structures and phylogeny. Analysis of pseudo-testcross (Pt) mapping data from F 1 families revealed mixed patterns of Mendelian and non-Mendelian segregation. Three-dimensional (3D) cytogenetic analysis of late meiotic prophase nuclei from two wild and two cultivated hop revealed conspicuous and prevalent occurrences of multiple, atypical, nondisomic chromosome complexes including autosomes. We used genome-wide association studies (GWAS) and fixation index (F st ) analysis to demonstrate selection mapping of genetic loci for key traits including sex, bitter acids, and drought tolerance. Among the possible mechanisms underlying the observed segregation distortion from the genomic data analysis, the cytogenetic analysis points to meiotic chromosome behavior as one of the contributing factors. The findings shed light on long-standing questions on the unusual transmission genetics and phenotypic variation in hop, with major implications for breeding, cultivation, and the natural history of Humulus.

No abstract

Hop (Humulus lupulus L.) is an important crop worldwide, known as the main flavoring ingredient in beer. The diversifying brewing industry demands variation in flavors, superior process properties, and sustainable agronomics, which are the focus of advanced molecular breeding efforts in hops. Hop breeders have been limited in their ability to create strains with desirable traits, however, because of the unusual and unpredictable inheritance patterns and associated non-Mendelian genetic marker segregation. Cytogenetic analysis of meiotic chromosome behavior has also revealed conspicuous and prevalent occurrences of multiple, atypical, non-disomic chromosome complexes, including those involving autosomes in late prophase. To explore the role of meiosis in segregation distortion, we undertook 3D cytogenetic analysis of hop pollen mother cells stained with DAPI and FISH. We used telomere FISH to demonstrate that hop exhibits a normal telomere clustering bouquet. We also identified and characterized a new sub-terminal 180 bp satellite DNA tandem repeat family called HSR0, located proximal to telomeres. Highly variable 5S rDNA FISH patterns within and between plants, together with the detection of anaphase chromosome bridges, reflect extensive departures from normal disomic signal composition and distribution. Subsequent FACS analysis revealed variable DNA content in a cultivated pedigree. Together, these findings implicate multiple phenomena, including aneuploidy, segmental aneuploidy, or chromosome rearrangements, as contributing factors to segregation distortion in hop.

No abstract