Mitotic and meiotic studies on two species of Ocimum (Lamiaceae) and their F1 hybrids

Abstract Ocimum L. species are important aromatic and medicinal plants. Many researchers have observed complexity in their chromosome numbers and ploidy levels. We studied the somatic and germline chromosomal features and behaviour of Ocimum basilicum L., two variants of O. canum Sims (‘c1’ and ‘c2’) and their F1 hybrids. Chromosomes from root tips and flower buds were investigated using standard techniques; karyograms were formed and analysed. A chromosome number of 2n = 4x = 52 was observed in O. basilicum and O. canum ‘c1’ and their F1 hybrid. One of the variants, O. canum ‘c2’ had a chromosome number of 2n = 2x = 24 and its intraspecific hybrid O. canum ‘c2’ × O. canum ‘c1’ had a chromosome number of 2n = 38. These Ocimum species and their F1 hybrids showed different karyotype formula, but their chromosomes were mostly metacentric (174) and submetacentric (36) with few subtelocentric (8). Based on pairing configuration, O. basilicum is an allotetraploid plant, O. canum ‘c1’ is an autotetraploid plant and the O. canum ‘c1’ is a diploid. The F1 hybrids showed higher frequency of meiotic abnormalities than the parents. The study showed intraspecific and interspecific variation in chromosome numbers and pairing patterns, but the chromosomes of the Ocimum species were similar in their centromeric positions.