Chromosome Evolution Based on Variation in Chromosome Number and Chiasma Frequency in the Genus <i>Ocimum</i> L. from Thailand

Abstract

Basil, Ocimum L., is an economically important member of the family Lamiaceae. It has been widely used for many purposes, such as culinary herbs. The genus harbors large variation in chromosome number and size, which is believed to be a consequence of centuries of cultivation and selection for desirable traits. Meiosis was examined in five Ocimum species from Thailand, from five populations of each species. The results revealed that three of these species are cytogenetically related, forming a polyploid series with a base chromosome number of x=13: O. americanum L. (2n=2x=26, a new number for Thai plants), O. basilicum L. (2n=4x=52) and O. africanum Lour. (2n=6x=78, a new number for the genus). Two species with small chromosomes, O. tenuiflorum L. (2n=36) and O. gratissimum L. (2n=40), seem probably tetraploids with base numbers x=9 and 10, respectively. Meiotic irregularities in O. basilicum and O. africanum suggested that the species may be newly formed polyploids undergoing diploidization. Unlike recent polyploids, the meiotic chromosomes of O. tenuiflorum and O. gratissimum are entirely stable. Statistically significant intraspecific variation in chiasma frequencies was found in O. basilicum and O. africanum and the variation appeared to be geographically associated. The results presented here are useful both in the conservation of native basil species and in the breeding of elite accessions.

Chromosome number variation in the genus <i>Acmella</i> (Asteraceae) from Thailand

“…Ramsey and Schemske (2002) reported that induced autopolyploid species showed higher bivalent (low frequency of chiasmata) and lower multivalent (high frequency of chiasmata) pairing than expected. The reduction in meiotic recombination represented a high percentage of bivalents (diploid-like behavior) and a low percentage of multivalents were observed in several genera with polyploid series, including Senecio (Asteraceae), Bulbosus (Poaceae), and Ocimum (Lamiaceae) (Sieber and Murray 1980, Lopez et al 2005, Lopez et al 2013, Lekhapan et al 2019. This diploid-like mechanism decreases irregular meiotic behavior to produce viable gametes and increases pollen fertility, as observed in genus Senecio.…”

“…In addition to translocation, inversion and/or transposition were hypothetically proposed in chromosome evolution in the South American and European species of Hypochaeris (Cerbah et al 1998, Weiss-Schneeweiss et al 2003, 2008 and genus Lactuca (El-Esawi and Sammour 2014), leading to karyotypic polymorphism within/among populations. Variations in karyotype formula and/or satellite position were also observed in other plant taxa, such as genus Crotalaria (Fabaceae), genus Fragaria (Rosaceae), and genus Ocimum (Lamiaceae) (Nathewet et al 2010, Tapia-Pastrana et al 2018, Lekhapan et al 2019.…”

Cytogenetic Toxicity and Infertile Properties of the Aqueous Extract of Cucumis melo Seeds (Cucurbitaceae) in Male Zonocerus variegatus Cell Model (Orthoptera: Pyrgomorphidae)

“…Abnormal sperm had either an aneuploid or a polyploid due to poor homolog separation at anaphase-1. In the same context, the authors [43,22,44,45,46,[47][48][49][50] proved the infertile effect of the cytogenotoxicity of two aqueous extracts.…”