Sex determination in hop is currently limited to phenotypic evaluation in the second year of growth. Earlier sex determination at the seedling stage is desirable for breeding and cultivation of hop: one approach is the use of molecular markers. Recently, 730 polymorphic markers from 92 hop accessions were discovered using diversity arrays technology (DArT; Howard et al. 2011), which were further used in linkage studies. Six of these DArT markers showed linkage with the male phenotype and were evaluated as potential male markers. PCR amplification conditions could be optimised for four of these six markers. PCR was carried out on 123 female and 44 male hop plants, both cultivated and wild, from a broad range of geographic locations. None of the four DArT male markers amplified in any female plant. Non-amplification in a few male plants of Japanese, North American or hybrid origin was observed when using single markers, but all males were identified by summing the results of all four markers. Also primers for amplifications of fragments of different lengths were designed and a triplex PCR assay was established. Interestingly, a length polymorphism in amplified fragments was identified when using one particular DArT male marker among some hop accessions. Sequencing identified a deletion of 52 bp mainly in hop accessions of American or mixed origin. The four new DArT male specific markers could be directly used in hop breeding programmes.
B.06 Other
COBISS.SI-ID: 7296121Flow cytometric analysis of 58 monoecious hops, progenies of various crosses of diploid parents, revealed that a high percentage of intersexes were of triploid genotype. In the natural system, polyploids in plants most commonly arise through the involvement of unreduced gametes. The ploidy level of pollen nuclei of five pollinating lines was studied by flow cytometry, using a newly established procedure based on disruption of pollen grains by chopping in frozen buffer in order to determine whether the causal factor for triploid formation is unreduced pollen grains. Pollen ploidy screening revealed no evidence of unreduced male gametes in any of the males analysed. Inheritance analysis of parental alleles using six codominant SSR markers was therefore employed and it was demonstrated that paternal unreduced gametes were mainly involved in the occurrence of triploidy. No clear correlations between nuclear DNA content and type of sex expression in diploid hops were found, with the exception that male hops showed the lowest nuclear DNA amount, although a male reverting from a monoecious plant had a higher value.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 7265913