© 2013 The Mendel Society Cytologia 78(2): 151–156

Karyotypic Studies of benghalensis variety benghalensis and C. forskalaei () from Nigeria

Matthew Oziegbe*, and Peter Olufemi Eludini

Department of Botany, Obafemi Awolowo University, Ile-Ife, Nigeria.

Received November 1, 2012; accepted March 18, 2013

Summary The study investigated the mitotic chromosomes of two variants of C. benghalensis var. benghalensis and C. forskalaei from Nigeria using classical cytogenetic techniques. The two variants of C. benghalensis var. benghalensis have the same diploid chromosome number of 2n=22 and the same karyotype formula of (8 m+10 sm+4 st) chromosomes. The two variants of C. forskalaei have the same diploid chromosome number of 2n=30 and the same karyotype formula of (14 m+ 6 sm+10 st) chromosomes. Terminal satellites were observed on the short arms of sub-terminal chro-

mosome pair number 13 of C. forskalaei cf1 and the short arms of sub-terminal chromosome pair number 7 of C. forskalaei cf2. No satellites were observed in the chromosomes of the two variants of C. benghalensis. The chromosomes of the two variants of C. benghalensis var. benghalensis are mainly medium sized (1.00–1.43 µm) while the chromosomes of C. forskalaei are mainly small sized (0.47–0.97 µm). Results indicate interspecific variation in chromosome numbers and forms in the two Commelina species investigated.

Key words Commelina benghalensis, Commelina forskalaei, Chromosome number, Karyotype.

Commelina benghalensis var. benghalensis J. K. Morton and C. forskalaei Vahl are two Commelina species that produce both aerial and underground cleistogamous flowers. Commelina benghalensis could be annual or perennial while C. forskalaei variants are mainly annual. In C. forskalaei, the aerial and underground flowers produce one per , because of the abortion of the developing dorsal . Commelina benghalensis produces five seeds in the aerial flower and three seeds in the underground flower. Commelina benghalensis and C. forskalaei are associated with disturbed soils, such as yards, lawns and cultivated areas, especially in cotton crops and orange groves (Faden 1993, Webster et al. 2005, Faden 2012). In Nigeria, C. benghalensis is mostly found in forest through the Guinea savanna areas (Hutchinson and Dalziel 1968). Commelina forskalaei is widely distributed in Africa, except in forested areas, as it is found only in savanna and drier parts of Nigeria (Hutchinson and Dalziel 1968). Variation in colour occurs within members of the same species in the genus Commelina. In C. benghalensis and C. forskalaei, petal colour may be blue or purple. Cytologically, the genus Commelina is complex with various chromosome counts between and within species. In Commelina, the basic chromosome number of X=7, X=11 and X=13–15 have been reported, of which the most common are X=14 and 15 (Jones and Jopling 1972, Chimphamba 1973). Grabiele et al. (2005) mentioned that the genus Commelina is poorly known karyotypically. Umoh et al. (1991) reported that little information is available on the cytogenetics of the genus Commelina in Africa. There are few reports on the mitotic chromosome studies of the members of the genus and there no reports of karyotype studies on the Commelina species in Nigeria. This study investigated mitotic chromosome forms in variants of C. benghalensis var. benghalensis and

* Corresponding author, e-mail: [email protected] DOI: 10.1508/cytologia.78.151 152 M. Oziegbe, and P. O. Eludini Cytologia 78(2)

C. forskalaei in order to understand intra-specific and inter-specific relationship and karyotype evolution in the genus.

Materials and methods

Two variants of C. benghalensis var. benghalensis J. K. Morton and C. forskalaei Vahl that differ in petal colour were collected from different populations in Nigeria. Commelina benghalensis var. benghalensis cb1, with a light purple petal colour, and C. benghalensis var. benghalensis cb2, with a light blue petal colour, were collected from Ile-Ife (7°28′14.54″N, 4°33′23.94″E) and Ilorin

(8°29′29.96″N, 4°32′40.71″E). Commelina forskalaei cf1, with a light purple petal colour, and C. forskalaei cf2, with a deep blue petal colour, were collected from Jebba (9°7′9.31″N, 4°49′34.11″E). Voucher specimens of each species and variants collected were deposited at the IFE herbarium Obafemi Awolowo University, Ile-Ife. were grown from stem cuttings and allowed to flower. Young plantlets were placed in transparent bottles filled with water for the growth of root tips. Somatic chromosomes were examined for plants from each Commelina variant by pretreating actively growing root tips harvested between 9.00 a.m. and 10.00 a.m. with 0.002 M of 8-hydroxy- quinoline solution for 4 h at room temperature, fixed in acetic acid : absolute ethanol (1 : 3) for at least 12 h. Root tips were macerated in 18% hydrochloric acid for 10 min, squashed and stained for 10 min in modified Orcein (Olorode 1974). Photomicrographs of selected mitotic cells were docu- mented with an AmScope MT microscope camera version 3.0.0.1 attached to a light microscope. For karyotypic description, chromosomes were classified into groups on the basis of centro- mere position (median, m; sub-median sm; sub-terminal, st) (Levan et al. 1964) and arranged in order of decreasing size. Average chromosome counts and measurements were calculated from 10 metaphase plates. The short arm length, long arm length, arm ratio (long arm length/short arm length), centromic index, longest/smallest chromosome ratio and proportion of chromosome pairs with arm ratio >2 were determined from measurements. The chromosome karyotypes were further classified into Stebbins category (Stebbins 1971).

Results

The two variants of C. benghalensis var. benghalensis showed a chromosome number of 2n=22 (Figs. 1A–C). The two variants of C. forskalaei showed a chromosome number of 2n=30

(Figs. 1D–F). The karyotype formula of C. benghalensis var. benghalensis cb1 consists of 8 me- dian, 10 sub-median and 4 sub-terminal chromosomes (8 m+10 sm+4 st) (Fig. 2A). The mean chro- mosome length of C. benghalensis var. benghalensis cb1 ranges from 1.00–1.40 µm, meaning all chromosomes are medium sized (Table 1). The mean centromic idex of C. benghalensis var. benghalensis cb1 is 35.63, the longest/smallest chromosome ratio is 1.40 and the proportion of chro- mosomes with arm ratio ˃2 is 0.55, which places the karyotype in the 3A Stebbins category. The karyotype formula of C. benghalensis var. benghalensis cb2 consists of 8 median, 10 sub-median and 4 sub-terminal chromosomes (8 m+10 sm+4 st) (Fig. 2B). The mean chromosome length of

C. benghalensis var. benghalensis cb2 ranges from 1.01–1.65 µm, meaning all chromosomes are medium sized (Table 1). The mean centromic index of C. benghalensis var. benghalensis cb2 is 34.89, the longest/smallest chromosome ratio is 1.63 and the proportion of chromosomes with arm ratio ˃2 is 0.45, which places the karyotype in the 2A Stebbins category. The karyotype formula of

C. forskalaei cf1 consists of 14 median, 6 sub-median and 10 sub-terminal chromosomes (14 m+6 sm+10 st) (Fig. 3A) with terminal satellites on the short arm of sub-terminal chromosome pair 13 (Fig. 3A). The mean chromosome length of C. forskalaei cf1 ranges from 0.63–1.07 µm and the chromosomes are mostly small sized, except for chromosome pairs 1 and 2, which are medium sized (Table 2). The mean centromic index of C. forskalaei cf1 is 31.53, the longest/smallest chro- 2013 Chromosome Studies in Two Commelina Species from Nigeria 153

Fig. 1. Mitotic chromosomes of C. benghalensis var. benghalensis and C. forskalaei variants. A.

Prometaphase in C. benghalensis (2=2x=22). B. Metaphase in C. benghalensis cb1. C. Metaphase in C. benghalensis cb2. D. Prometaphase in C. forskalaei (2=2x=30). E. Metaphase in C. forskalaei cf1. F. Metaphase in C. forskalaei cf2. Scale=10 µm.

Fig. 2. Karyotypes of C. benghalensis variants (2=2x=22). A. C. benghalensis cb1 B. C. benghalensis cb2. Scale=6 µm. mosome ratio of is 1.70 and the proportion of chromosomes with arm ratio ˃2 is 0.40, which places the karyotype in the 2A Stebbins category. The karyotype formula of C. forskalaei cf2 consists of 14 median, 6 sub-median and 10 sub-terminal chromosome (14 m+6 sm+10 st) (Fig. 3B) but with terminal satellites on the short arm of sub-terminal chromosome pair 7 (Fig. 3B). The mean chro- mosome length of C. forskalaei cf2 ranges from 0.47–1.08 µm and the chromosomes are mostly small sized chromosomes, except for chromosome pair 1, which is medium sized (Table 2). The mean centromic index of C. forskalaei cf2 is 35.39, the longest/smallest chromosome ratio of is 2.30 and the proportion of chromosomes with arm ratio ˃2 is 0.40 which places the karyotype in the 2B Stebbins category (Table 2). 154 M. Oziegbe, and P. O. Eludini Cytologia 78(2)

Table 1. Karyotype data on arms length and centromic position of C. benghalensis var. benghalensis variants

C. benghalensis var. benghalensis cb1 C. benghalensis var. benghalensis cb2 Chromo some MSL MLL MSL+ Arm MSL MLL MSL+ Arm pair number CP CT CP CT (µm) (µm) MLL(µm) ratio (µm) (µm) MLL(µm) ratio

1 0.50±0.01 0.90±0.03 1.40±0.14 1.80 sm B 0.68±0.03 0.97±0.05 1.65±0.15 1.43 m B 2 0.43±0.02 0.90±0.04 1.33±0.05 2.09 sm B 0.39±0.02 1.20±0.03 1.59±0.04 3.08 st B 3 0.50±0.01 0.79±0.02 1.30±0.03 1.58 m B 0.47±0.01 0.97±0.02 1.44±0.12 2.06 sm B 4 0.32±0.01 0.83±0.01 1.15±0.13 2.59 sm B 0.50±0.04 0.90±0.01 1.40±0.06 1.80 sm B 5 0.46±0.03 0.68±0.02 1.14±0.03 1.48 m B 0.62±0.01 0.69±0.02 1.31±0.13 1.11 m B 6 0.47±0.00 0.65±0.01 1.12±0.04 1.38 m B 0.47±0.00 0.83±0.05 1.30±0.03 1.77 sm B 7 0.33±0.01 0.76±0.03 1.09±0.02 2.30 sm B 0.36±0.02 0.90±0.01 1.26±0.04 2.50 sm B 8 0.14±0.00 0.94±0.05 1.08±0.11 6.71 st B 0.36±0.01 0.86±0.03 1.22±0.14 2.39 sm B 9 0.50±0.02 0.58±0.03 1.08±0.02 1.16 m B 0.53±0.03 0.67±0.02 1.20±0.05 1.26 m B 10 0.25±0.00 0.79±0.04 1.04±0.03 3.16 st B 0.29±0.00 0.90±0.01 1.19±0.02 3.13 st B 11 0.32±0.00 0.68±0.01 1.00±0.02 2.13 sm B 0.40±0.01 0.61±0.03 1.01±0.11 1.53 m B

Total 4.22±0.11 8.50±0.29 12.73±0.62 5.07±0.18 9.50±0.28 14.57±0.89

* Mean±SD, MSL=Mean Short Arm; MLL=Mean Long Arm, CP=Centromic position: m=median, sm=Sub-median, st=Sub-terminal. CT=Chromosome Type: A is greater than 2.01µms=large, B=1.01–2.01 µm=medium; C lesser or equal to 1.01 µm=small

Table 2. Karyotype data on arm length and centromic position of C. forskalaei variants

C. forkskalaei cf1 C. forkskalaei cf2 Chromosome MSL MLL MSL+ Arm MSL MLL MSL+ Arm pair number CP CT CP CT (µm) (µm) MLL (µm) ratio (µm) (µm) MLL (µm) ratio

1 0.39±0.01 0.68±0.13 1.07±0.05 1.81 sm B 0.40±0.01 0.68±0.01 1.08±0.03 1.70 sm B 2 0.36±0.01 0.68±0.02 1.04±0.14 1.89 m B 0.28±0.01 0.58±0.03 0.86±0.02 2.07 sm C 3 0.36±0.02 0.61±0.12 0.97±0.02 1.69 m C 0.28±0.00 0.47±0.01 0.75±0.02 1.68 m C 4 0.39±0.11 0.57±0.14 0.96±0.11 1.50 m C 0.18±0.00 0.57±0.02 0.75±0.04 3.17 st C 5 0.36±0.13 0.58±0.13 0.94±0.03 1.61 m C 0.29±0.01 0.43±0.01 0.72±0.11 1.48 m C 6 0.32±0.01 0.50±0.03 0.82±0.11 1.56 m C 0.23±0.01 0.42±0.01 0.65±0.02 1.83 sm C 7 0.14±0.13 0.65±0.01 0.79±0.13 4.64 st C 0.10±0.00 0.53±0.03 0.63±0.02 4.91 st C 8 0.20±0.01 0.56±0.04 0.76±0.14 2.64 sm C 0.14±0.00 0.47±0.02 0.61±0.03 3.36 st C 9 0.12±0.01 0.62±0.15 0.74±0.04 5.17 st C 0.29±0.00 0.29±0.00 0.58±0.01 1.00 m C 10 0.14±0.01 0.61±0.01 0.70±0.06 4.36 st C 0.29±0.01 0.29±0.01 0.58±0.01 1.00 m C 11 0.32±0.01 0.36±0.02 0.68±0.04 1.13 m C 0.29±0.00 0.29±0.00 0.58±0.00 1.00 m C 12 0.32±0.01 0.36±0.13 0.68±0.02 1.13 m C 0.29±0.00 0.29±0.00 0.58±0.01 1.00 m C 13 0.15±0.00 0.51±0.02 0.66±0.01 3.57 st C 0.22±0.00 0.36±0.01 0.58±0.01 1.64 m C 14 0.22±0.01 0.43±0.01 0.65±0.13 1.95 sm C 0.14±0.00 0.43±0.01 0.57±0.02 3.07 st C 15 0.10±0.00 0.53±0.12 0.63±0.03 4.07 st C 0.11±0.00 0.36±0.01 0.47±0.01 3.27 st C

Total 3.89±0.48 8.25±1.08 12.09±1.06 3.53±0.05 6.46±0.18 9.99±0.36

* Mean±SD, MSL=Mean Short Arm; MLL=Mean Long Arm, CP=Centromic position: m=median, sm=Sub-median, st=Sub-terminal. CT=Chromosome Type: A is greater than 2.01 µsm=large, B=1.01–2.01 µm=medium; C lesser or equal to 1.01 µm=small

Discussion

The chromosome counts of 2n=22 observed in the two variants C. benghalensis have been the most reported for this species (Moore 1973, Fedorov 1974, Goldblatt 1981, 1984, 1988, Goldblatt and Johnson 1990, 1998, 2000, Yang and Kang 2004, Kaul et al. 2007, Grabiele et al. 2009). Commelina benghalensis var. hirsuta has been reported as exclusively polyploid with a chromo- 2013 Chromosome Studies in Two Commelina Species from Nigeria 155

Fig. 3. Karyotypes of C. forskalaei variants (2=2x=30). A. C. forskalaei cf1 B. C. forskalaei cf2. Scale=6 µm. some number of 2n=44 and 66 (Jones and Jopling 1972, Fedorov 1974, Moore 1977, Faden 2005). Only Commelina communis L. has been reported to share the same chromosome number of 2n=22 with C. benghalensis var. benghalensis within the genus (Wang et al. 1994). There are other cyto- types within C. communis which are polyploids, 2n=44 and 88, which share the basic chromosome number of X=11 with C. benghalensis (Fujishima et al. 2004). There are few reports on chromo- some counts of C. forskalaei. The chromosome counts of 2n=30 observed correspond to the report of Faden (1993) for C. forskalaei from the U.S.A. This chromosome number has been the most frequent within members of the genus Commelina (Grabiele et al. 2005). The interspecific varia- tion in chromosome number observed in this study has been reported to be common within species and between species in this genus (Grabiele et al. 2005). The basic chromosome number of x=11, 13–15 has been reported for this genus (Jones and Jopling 1972, Bhattacharya 1975). The karyo- type formula of 8 m+10 sm+4 st with no satellites, observed in C. benghalensis, differs slightly from those reported by earlier researchers. Grabiele et al. (2009) reported the same karyotype formula of 8 m+10 sm+4 st but with terminal macro satellites on chromosome pair number 11 for C. benghalensis from Argentina. Kaul et al. (2007) reported a karyotype formula of 18 sm+4 st with satellites on the short arms of sub-terminal chromosome pairs numbers 5 and 8, respectively, for C. benghalensis from India. Yang and Kang (2004) reported a karyotype formula of 12 m+8 sm+2 st for C. benghalensis from . Wang et al. (1994) reported a karyotype formula of 18 m+4 sm for C. benghalensis from China. The variation in karyotype formula within members of the same species in the genus Commelina was reported by Fujishima et al. (2004). The data presented here comprise the first report on the karyological description of C. forskalaei. The karyotype formula of 14 m+6 sm+10 st differs greatly from that of C. benghalensis. Result show that the chromosomes of C. benghalensis are mostly median and sub-median chromosomes while the chromosomes of C. forskalaei are mostly median and sub-terminal chromosomes. The presence of more sub-terminal chromosomes in C. forskalaei is a characteristic of advancement. Most karyotype studies in the genus Commelina reported more median and sub-median chromosomes but few sub-terminal chro- mosomes (Fujishima et al. 2004, Grabiele et al. 2005). The medium sized chromosomes observed in the two variants of C. benghalensis in this study correspond to the work of Yang and Kang (2004) and Grabiele et al. (2009) who similarly reported that the chromosomes of C. benghalensis from China and Argentina are medium sized. The medium sized chromosomes of C. benghalensis are quite different from the small sized chromosomes observed in C. forskalaei. Bhattacharya (1975) reported that chromosomes of genus Commelina range from medium sized to small sized. The results indicate that the karyotype of each variant of C. benghalensis and C. forskalaei belongs to a different Stebbins category. The 3A Stebbins category observed in C. benghalensis cf1 corresponds 156 M. Oziegbe, and P. O. Eludini Cytologia 78(2) to the 3A reported by Grabiele et al. (2009) for C. benghalensis from Argentina. Yang and Kang (2004) reported the 2B Stebbins category for C. benghalensis from China. Grabiele et al. (2005) reported that the chromosomes of Commelina belong to the 2A and 2B Stebbins categories. The results of this study show that there is no variation in chromosome number, karyotype formula and chromosome size within members of the same species studied, but did indicate inter-specific variation within these parameters. The karyotype of C. forskalaei indicates advancement over C. benghalensis.

References

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