The Lowest Chromosome Number and Chromosome Evolution in <i>Begonia</i> sect. <i>Platycentrum</i> (Begoniaceae) with Lower Chromosome Numbers

Abstract

Previous chromosome information for the lower chromosome numbers 2n=14, 16, 18, and 20 in Asian Begonia are restricted to nine species in two sections Diploclinium and Platycentrum. Here we report the first chromosome counts of four species as well as reconfirmed chromosome numbers of four species in sect. Platycentrum. We found 2n=12 in B. cathcartii, the lowest chromosome number known for the genus. The number of species with lower chromosome numbers reported is increased to 13 species in sections Diploclinium and Platycentrum. Additionally, we provide the first report of karyotypes of seven species with the lower chromosome numbers in sect. Platycentrum. Based on the present results and previous chromosome reports for a total of 13 species with lower chromosome numbers, the chromosome evolution for them is discussed.

Cytological study of <i>Begonia</i> sect. <i>Platycentrum</i> (Begoniaceae) with chromosome numbers 2<i>n</i>=24, 26, and 52

“…Platycentrum have 10 m-chromosomes and two smchromosomes in common. Consequently, our studies of Asian Begonia cytology show that all chromosome variants (ranging from 2n=12 to 44) within 10 sections [i.e., Baryandra (Kono et al 2021a), Coelocentrum (Kono et al 2020), Diploclinium (Kono et al 2021b), Flocciferae (Kono et al 2023a), Haagea (Kono et al 2022a), Jackia (Kono et al 2023b), Parvibegonia (Kono et al 2023a), Petermannia (Kono et al 2022a), Platycentrum (Kono et al 2022b, c), and Reichenheimia (Kono et al 2023b)], consistently have two or four sm-chromosomes within their respective chromosome complements in common.…”

“…The centric fissions also play a role in chromosome evolution in Asian Begonia. Kono et al (2022b) suggested that the karyotype 2n=18= 6m+ 8sm+ 2st+ 2t in B. tamdaoensis could have originated from 2n=14= 10m+ 4sm(st) 2sm through centric fission and subsequent translocation. By centric fission on the fused m-chromosomes (e.g., No.…”

“…In summary, the karyotypes of Asian Begonia 2n=28= 10m+ 18sm(st) 2sm , 2n=26= 10m+ 16sm(st) 2sm , 2n=24= 10m+ 14sm(st) 2sm , 2n=22= 12m+ 10sm(st) 2sm , and 2n=22= 8m+ 14sm(st) 2sm might be derived from 2n=30= 8m+ 22sm(st) 2sm , and those of the lower chromosome variants 2n=20= 10m+ 10sm(st) 2sm , 2n=18= 10m+ 8sm(st) 2sm , 2n=16= 10m+ 6sm(st) 2sm , 2n=14= 10m+ 4sm(st) 2sm , and 2n=12= 10m+ 2sm(st) from 2n=22= 8m+ 14sm(st) 2sm by chromosome fusion, respectively (Kono et al 2022b(Kono et al , 2022c(Kono et al , 2023a, the present study). Consequently, chromosome variants 2n=28, 26, 24, 22, 20, 18, 16, 14, and 12 in sections Baryandra, Diploclinium, and Platycentrum might be derived from 2n=30= 8m+ 22sm(st) 2sm through chromosome fusion.…”

Cytological Study of <i>Begonia</i> Sections <i>Flocciferae</i>, <i>Parvibegonia</i> and <i>Platycentrum</i> (Begoniaceae) with Chromosome Numbers 2<i>n</i>=28 and 56

“…The chromosome number 2n=56 in B. baliensis is the first such count in sect. Platycentrum (Kono et al 2022b(Kono et al , 2022c. Its karyotype 2n=56= 20m+ 36sm(st) 4sm consists of four sets of 14 chromosomes of n=5m+ 9sm(st) 1sm , suggesting that the species is tetraploid of 2n=28= 10m+ 18sm(st) 2sm .…”

Cytological Study of <i>Begonia</i> Sections <i>Jackia</i>, <i>Platycentrum</i> and <i>Reichenheimia</i> (Begoniaceae) with Chromosome Numbers 2<i>n</i>=34 and 38

“…A.DC. proposed by Kono et al (2022c); B. bipinnatifida J.J.Smith with 2n= 44= 16m+ 28sm(st) 4sm and B. holttumii Irmsch. with 2n= 60= 16m+ 44sm(st) 4sm in sect.…”