Cytogenetics, Ploidy, and Genome Sizes of Camellia and Related Genera

Abstract

<jats:p><jats:italic>Camellia</jats:italic> L., the most speciose member of the diverse tea family Theaceae, has a long and complex horticultural history. Extensive cultivation and hybridization have produced thousands of varieties of <jats:italic>Camellia</jats:italic>, including commercially important crops such as cultivated tea, oilseed, and iconic flowering shrubs. Cytogenetics of <jats:italic>Camellia</jats:italic> and related genera is complicated; chromosome number and ploidy can vary widely between species, and interspecific and interploid hybridization occurs. However, specific information regarding cytogenetics of many species, cultivars, and modern hybrids is lacking. The objectives of this study were to compile a consolidated literature review of the cytogenetics of <jats:italic>Camellia</jats:italic> and related genera and to determine chromosome numbers, ploidy, and genome sizes of specific accessions of selected species, cultivars, and interspecific and interploid hybrids. A review of the existing literature regarding Theaceae cytogenetics is presented as a consolidated reference comprising 362 taxa. Genome sizes were determined with flow cytometry using propidium iodide as a fluorochrome and <jats:italic>Pisum sativum</jats:italic> ‘Ctirad' and <jats:italic>Magnolia virginiana</jats:italic> ‘Jim Wilson’ as internal standards. Chromosome numbers of selected taxa were determined using traditional cytology and were used to calibrate genome sizes with ploidy level. Our results confirmed a base chromosome number of <jats:italic>x</jats:italic> = 15 for Theeae including <jats:italic>Camellia</jats:italic>, <jats:italic>x</jats:italic> = 17 for Stewartiae, and <jats:italic>x</jats:italic> = 18 for Gordoniae. Surveyed camellias ranged from 2<jats:italic>n</jats:italic> = 2<jats:italic>x</jats:italic> = 30 to 2<jats:italic>n</jats:italic> = 8<jats:italic>x</jats:italic> = 120, including diploids, triploids, tetraploids, pentaploids, hexaploids, and octoploids. Previously uncharacterized taxa such as <jats:italic>Camellia azalea</jats:italic>, <jats:italic>C. amplexicaulis</jats:italic>, <jats:italic>C. chrysanthoides</jats:italic>, <jats:italic>C. cordifolia</jats:italic>, <jats:italic>C. cucphuongensis</jats:italic>, <jats:italic>C. flava</jats:italic>, <jats:italic>C. nanyongensis</jats:italic>, and <jats:italic>C. trichoclada</jats:italic> were found to be diploid. Ploidy was also newly determined for <jats:italic>Schima argentea</jats:italic>, <jats:italic>S. khasiana</jats:italic>, <jats:italic>S. remotiserrata</jats:italic>, and <jats:italic>S. sinensis</jats:italic> (all diploids). Both diploid and triploid <jats:italic>Stewartia ovata</jats:italic> were found, and a ploidy series was discovered for <jats:italic>Polyspora</jats:italic> that ranged from diploid to octoploid. Ploidy determinations were used to confirm or challenge the validity of putative interploid hybrids. Monoploid genome sizes varied among subfamily and genera, with 1C<jats:italic>x</jats:italic> values ranging from 0.80 pg for <jats:italic>Franklinia</jats:italic> to a mean of 3.13 pg for <jats:italic>Camellia</jats:italic>, demonstrating differential rates of genome expansion independent of ploidy<jats:italic>.</jats:italic> Within <jats:italic>Camellia,</jats:italic> monoploid genome sizes varied among subgenera, sections, and some species (range, 2.70–3.55 pg). This study provides a consolidated and expanded knowledgebase of ploidy, genome sizes, hybridity, and reproductive pathways for specific accessions of <jats:italic>Camellia</jats:italic> and related genera that will enhance opportunities and strategies for future breeding and improvement within Theaceae.</jats:p>

Genetic Diversity and Genome Size Variability in the Russian Genebank Collection of Tea Plant [Camellia sinensis (L). O. Kuntze]

“…Particularly, most of the mutant forms derived from "Kolkhida" or "Quimen" seeds treated with G-irradiation showed increased genome size. Our results are consistent with other published data on tea, which indicated 2C DNA content in CSS ranged from 6.0-7.0 pg, whereas 4C DNA content was around 13.0 pg (Hembree et al, 2019). In CSA, the 2C DNA content ranged from 5.8-7.7 pg (Huang et al, 2013;Sharma et al, 2019).…”

“…Ploidy and genome size can influence reproductive compatibility, fertility, and heritability of traits wherefore these data can be useful for understanding breeding potential in collections (Hembree et al, 2019). Our results showed remarkable intraspecific variation in the genome size of the 43 selected genotypes.…”

“…"'Kolkhida":2C DNA content = 6.99 pg (Efremov et al, 2018) and C. sinensis cv. "Sochi, " 2C DNA content = 6.95 pg (Hembree et al, 2019). For each accession, three independent replicates from different plants were analyzed separately.…”

Phylogenetics of global Camellia (Theaceae) based on three nuclear regions and its implications for systematics and evolutionary history

“…Clade Camellia II contains C. granthamiana , C. grijsii , C. shensiensis , and some members of the sect. Camellia , which generally have polyploids (Ming, 2000; Hembree et al, 2019) and are distributed in central, southern, and south‐western China. Chang (1996) established sect.…”

Oil plant genomes: current state of the science

“…Compared with mammals, plants contain more polygene families and higher frequency of polyploidy (Lockton and Gaut, 2005). Many conventional and newly developed oil crops have tetraploid or hexaploid genomes, such as cotton, rapeseed, Brassica juncea, peanut, oil tea, and camelina (Chalhoub et al, 2014;Hembree et al, 2019;Li et al, 2015;Yang et al, 2016;Zhuang et al, 2019). The genomic research of oil plants covers the origin of subgenome, expression advantage, gene function differentiation, genome reorganization, and asymmetric evolution (Cheng et al, 2014;Liu et al, 2014;Parkin et al, 2014;Yang et al, 2016).…”