Karyotype Analysis and Ploidy Determination Using Flow Cytometry in African Bitter Milk Plant “Utazi”, <i>Gongronema latifolium</i> Benth

Abstract

Availability of basic genetic information on a plant species is the first pre-requisite in designing any genetic improvement programme for the species. This study was therefore carried out to determine the karyotype of Gongronema latifolium to obtain basic knowledge on ploidy level and karyotype as a first step in understanding the genetics of this spice plant. Karyotype and flow cytometry (FCM) studies were carried out on 4 accessions of G. latifolium collected from the humid forest vegetation in Abia, Akwa Ibom, Cross River and Imo States of Nigeria. Chromosome number of Abia accessions were 2n=20 and 22 with karyotype formulae, 3m+4sm+2a+1t and 2m+4sm+2a+3t, respectively; Akwa Ibom accessions, 2n=18 with formula: 3m+5sm+1a; Cross River accessions, 2n=18 and 22 with formulae: 2m+4sm+2a+1t and 3m+4sm+3a+1t, respectively; Imo accessions, 2x=22 and 24 with formulae: 1m+5sm+3a+2t and 2m+7sm+2a+1t, respectively. Results obtained revealed cytotype variation and the occurrence of 4 cytotypes, 2n=18, 20, 22 and 24. We therefore conclude that G. latifolium is a diploid species with variable basic numbers. Four basic numbers, n=9, 10, 11 and 12, were therefore proposed for G. latifolium. FCM showed the presence of 2C and 4C DNA content and provided evidence for endoreduplication, a likely evolutionary survival mechanism in this climbing vegetable plant species. This is the first report of karyotype analysis in Gongronema latifolium, an important indigenous African vegetable spice plant with huge medicinal value.