Abstract
We analysed chromosome lengths, karyotype structure, and nuclear DNA content (flow cytometry) in diploid (2n=20) and triploid (2n=30) European <em>H. lupulus</em> var. <em>lupulus</em>, American <em>H. lupulus</em> var. <em>neomexicanus</em> (2n=20) and Japanese ornamental hop, <em>H. japonicus</em> (F/2n=16; M/2n=17). Diploid female representatives of <em>H. lupulus</em> var. <em>lupulus</em> and <em>H. l.</em> var. <em>neomexicanus</em> differed in total length of the basal chromosome set (23.16 µm and 25.99 µm, respectively) and nuclear 2C DNA amount (5.598 pg and 6.064 pg) but showed similar karyotype structure. No deviation from the additivity, both in chromosome length and 2C DNA amount was evidenced in triploid monoecious <em>H. lupulus</em> (2n=30, XXY). <em>H. japonicus</em> showed different karyotype structure, smaller basal chromosome set (F/18.04 µm, M/20.66 µm) and lower nuclear DNA amount (F/3.208 pg and M/3.522 pg). There are first evaluations of nuclear genome size in diploid, not commercial representative of European <em>H. lupulus</em> var. <em>lupulus</em> and American <em>H. lupulus</em> var. <em>neomexicanus</em> and first attempt to determine the absolute male and female genome size in two Humulus species.
Highlights
The genus Humulus, one of two genera in the Cannabaceae family contains three species: H. lupulus, H. japonicus (=H. scandens (Lour.) Merr.) and H. yunnanensis (Small 1978). Both H. lupulus (European common hop) and H. japonicus (Japanese ornamental hop) are dioecious, climbing plants with sex chromosomes (Winge 1929) and sex determination system based on X/autosome balance (Parker and Clark 1991; Shepard et al 2000)
Humulus lupulus plants used in this study, all derived from Institute of Soil Science and Plant Cultivation, Pu3awy, Poland, are listed bellow: H. lupulus cv.Lubelski Polish diploid cultivar, released in 1964 as a noble aroma hop, is cultivated in Poland to date on an area of about 800 ha
H. lupulus is long recognized as the dioecious plant with sex chromosome system (Winge 1929; Jacobsen 1957; Westergaard 1958), its sex chromosomes are not easy to identify even in males, possessing heteromorphic sex chromosome pair
Summary
The genus Humulus, one of two genera in the Cannabaceae family contains three species: H. lupulus, H. japonicus (=H. scandens (Lour.) Merr.) and H. yunnanensis (Small 1978). Both H. lupulus (European common hop) and H. japonicus (Japanese ornamental hop) are dioecious, climbing plants with sex chromosomes (Winge 1929) and sex determination system based on X/autosome balance (Parker and Clark 1991; Shepard et al 2000). X/autosome ratio of 0.5 or less gives male phenotype, while a ratio of 1.0 gives rise to female plants. Triploids (2n=3x=27+XXY, X/A=0.67) are generally of male phenotype with only a few terminal female
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