Shang Zong-yan, Li Ru-juan, Cui Tie-cheng, Xu Jie-mei
1997, 35 (5): 434–444
Chromosomes of 14 populations of 8 species of Allium from China were observed
in the present work. The results are as follows: (1)A. tuberosum Rottl. ex Spreng: three
populations were studied and they were all tetraploids (2n=4x=32) with 28 m and 4 st on
which satellites usually appeared. The population 1 (C-1237) was found to have the karyotype 2n=4x=32=28m+4st(2SAT) (Fig. 1:1 ), the population 2(C-1188) 2n=4x=32=
28m+4st (4SAT) (Fig. 1: 2), and the population 3 (C-1179) with satellites ranging from one to three in number. In some cells we found that the satellites look like a string of beads (Fig.1: 3). (2) A. ramosum L.: the population 1 (C-1193) was diploid with the karyotype 2n =2x = 16 = 14m + 2st ( 2SAT ) ( Fig. 2: 2), while the population 2 (C-1307) was tetraploid with 2n=4x = 32 (Fig. 2:5). The number of sat-chromosomes ranged from zero to three. (3)
A. anisopodium Ledeb.: the population 1 (C-1313) was found to have the karyotype 2n=2x
=16=12m+ 4sm(2SAT) with a pair of terminal satellites ( Fig. 2:1), and the population 2 (C-1286) 2n=2x=16, with the satellite chromosomes exhibiting polymorphism (Fig 5). In
about 80% of cells, a chromosome was found to have a intercalary satellite, and thus the
karyotype became 2n=2x=16=14m+2sm(1SAT) (Fig. 2: 3). (4) A. anisopodium Ledeb. var. zimrmermannianum (Gilg) Wang et Tang (C-1253) was a diploid with 2n=2x=16. One pair of chromosomes had intercalary satellites, which were often detached from the chromosomes (Fig. 2:4). (5) A. nutans L. (C-1312) showed great intrapopulational variation in chromosome number. 2n= 4x=32, 2n=6x=48, 2n=8x=64 and 2n=9x=72 were found in different plants from the same population (Fig. 3: 1, 2, 3). (6) A. macrostemon Bunge(C-1245) had the chromosome number of 2n=4x=32. The satellite chromosomes exhibited polymorphism (Fig.2:6. Fig.5). (7) A. tubifiorum Rendle.: the population 1 (C-1279) was a diploid of 2n=2x= 16 with a pair of chromosomes with terminal satellites ( Fig. 3: 5), and the population 2 (C-1289) a tetraploid with 2n=4x=32,
with two pairs of chromosomes having terminal satellites(Fig. 3:4 ). (8) A. neriniflorum
(Herb.)Baker. The population 1 (C-1318) had the chromosome number of 2n=2x=16 with a pair of chromosomes having intercalary satellites. Non heterozygosity was found in this pair in 1991 (Fig.3: 6), but we found heterozygosity in 1992 (Fig. 3:7 ). The population 2 (C-1393) was also found to have 2n= 2x = 16. The heterozygous satellite chromosomes were found in a few root tips (Fig.3: 8. Fig.5).
Polyploidy is very common in Allium. Seven polyploid populations are reported in this
paper. Some species, such as A. ramosum and A. tubiflorum , had both diploid and tetraploid populations, while some others, such as A. nutans, had different plants respectively with 4x, 6x, 8x and 9x within populations.
We also found that in polyploids the number of satellite chromosomes was not always
correlated with ploidy level. Among the six tetraploids, two populations (C-1188, C-1289)
had four satellite chromosomes, two populations (C-1237, C-1245) had two and the other
two (C-1179, C-1307) had variable number (0～3) of satellites.
Fig. 1: 3 shows bead-like satellites on only one st chromosome among four in tetraploid
C-1179. It is supposed that the satellites of these three st chromosomes were transferred to that one and this“transfer”may lead to unstable number of satellites in polyploids.
Unlike number, the variation of satellite chromosomes in their morphology is more
closely correlated with external morphological characters. In the section Caloscordum, the
diploids of A. tubiflorum and A. neriniflorum have the same karyotype 2n = 2x = 16 =
12m + 4sm(2SAT), but there is a pair of chromosomes with terminal satellites in the former, while a pair of chromosomes with the intercalary satellites in the latter. Although they are quite similar, they are classified into two species. A similar situation is also found in A. anisopodium (C-1313 with a pair of chromosomes with terminal satellites) and its variety, var. zimmermannianum ( C-1253 with intercalary satellites); the latter has fine teeth on its scape. It is interesting to note that C-1286 seems to have fine teeth, as if this population is an intermediate type, and only one intercalary satellite chromosome is found in more than 80 % of cells. The morphological variation of satellite chromosomes might be one of possible causes leading to speciation.
We consider that the morphological variability and structural heterozygosity of satellitechromosomes are important sources of genetic variation and evolution in Allium.