Ploidy variation and agronomic performance of F₁ hybrids of tetraploid and diploid forms of Humulus lupulus L.

Abstract

Humulus lupulus (2n = 2x = 20) as a source of hop resins, essential oils and polyphenols has value in brewing, pharmacy and cosmetology. Conventional crossing between tetraploids of ‘Sybilla’ and diploid males were performed to obtain F₁ hybrids. Cytological studies revealed that 83.8% of the hybrids were triploids (2n = 3x = 30), 15.2% were aneuploids in which the chromosome number ranged from 28–32. Tetraploids (2n = 4x = 40) and diploids were also observed, which indicates numerous disturbances of gametogenesis of the parental forms. STS markers specific for male plants showed that females outnumbered male individuals among the F₁ hybrids, which is in accordance with the distribution of sex ratio characteristic for diploid hybrids of H. lupulus. Female triploids were compared to the control ‘Sybilla’ with regard to their functional characteristics and alpha acids content in cones. A two year-long experiment showed that most of the triploids had a significantly higher position of fructiferous branches and shoot twist index compared to diploids of ‘Sybilla’. There was also a significantly extended time for them to reach technological maturity of cones. Triploids were distinguished by a significantly lower seed content compared to ‘Sybilla’, therefore the raw material obtained from them is more suitable for the production of hop pellets and extracts.