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Chromosome Numbers and Cross-compatibility in the Genus Cymbidium and Some Related Tropical Genera (Orchidaceae)

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Title:Chromosome Numbers and Cross-compatibility in the Genus Cymbidium and Some Related Tropical Genera (Orchidaceae)
Authors:Leonhardt, Kenneth W.
Date Issued:1977
Abstract:Investigations on chromosome numbers and cross-compatibility were made with species and hybrids of Cymbidium and other tropical genera of the family Orchidaceae. Chromosome number determinations were made of 163 plants. One hundred nineteen counts of Cymbidium clones were made of which 92 are reported for the first time. Diploid, triploid, tetraploid, hexaploid and aneuploid individuals were determined. Triploid cultivars of two species, C. insigne 'Bierii' and C. pumilum 'Yashima' were found. Forty-four counts of intergeneric hybrids and genera other than Cymbidium were made. The hybrid status of 17 progenies of intergeneric pollinations was determined by analysis of somatic chromosome numbers. Nine plants derived from colchicine treated protocorms were identified as polyploids; 8 being euploid and 1 a mixoploid. The origin of the polyploid nature of some of the hybrids not subjected to colchicine treatments is discussed. It was verified cytologically that Cymbidium did hybridize with Ansellia and Catasetum. The origin of seedlings of 6 intergeneric pollinations is discussed. The origin of the registered but questionable hybrid Phaiocymbidium Chardwarense is discussed.
Cymbidium species were categorized into 3 groups (I, II, and III) based on morphological features of plants, flowers, and inflorescences. A cross-compatibility study was made utilizing 21 species and 28 hybrid Cymbidium and 26 species and hybrids of other genera. A total of 2,466 pollination was made with 265 (10.7%) fruits harvested of which 182 (68.7 %) contained an average of 31.3%, seeds with apparently viable embryos. One hundred forty-two fruits (53.6%, and 78.0%, of those that contained apparently viable embryos) produced seedlings. It has been demonstrated that species of groups I and II are more cross-compatible within groups than between groups. It is also demonstrated that species of groups I and II are more cross-compatible between these groups than they are with species of group III. Thirty-eight intergeneric pollinations resulted in seedlings of which 10 are confirmed hybrids, 2 are false hybrids and 26 were not verified cytologically. The discovery of a unidirectional cross-incompatibility system was made whereby Ansidium seedlings are rarely produced when Ansellia is used as a female parent and are easily produced when Cymbidium is used as a female. Individual Cymbidium species and hybrids were evaluated for their intra- and intergeneric combining abilities.
The diploid and tetraploid forms of _C. Peter Pan 'Greensleeves' were compared for 14 morphological features. A formula was developed for determining changes in symmetry as a result of polyploid induction.
A discussion of various incompatibility systems in the Orchidaceae is presented.
Criteria and recommendations for a breeding program designed to produce commercially acceptable Cymbidiums capable of flowering at low elevations in Hawaii are presented.
Appears in Collections: Ph.D. - Horticulture

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