Increased variation in volatile organic compound compositions and 2C DNA contents in Ocimum basilicum × tenuiflorum introgression lines

Abstract

Secondary gene pools are important sources of valuable traits, such as disease resistance, which can be introgressed into crop plants by interspecific hybridization. However, combining different genomes may cause chromosomal abnormalities in later generations resulting in loss of traits or new traits. This study describes an introgression breeding program based on an interspecific cross between Ocimum basilicum var. basilicum ‘Bavires’ and O. tenuiflorum ‘Tulsi’. Eighty-two introgression lines were generated through successive backcrosses with the Genovese-type cultivar ‘Bavires’. F3BC4S plants were analyzed for 2C DNA content, chromosome number, and volatile organic compound composition. Flow cytometry showed that most individuals had 2C DNA contents between 4.8 and 5.2 pg, corresponding to 52–54 chromosomes, though some had significantly higher 2C DNA contents corresponding to 56, 60, 63, 74, or 78 chromosomes. Gas chromatography-mass spectrometry analysis of leaves from 76 individuals identified 71 volatile compounds. Principal component analysis revealed that most volatile profiles clustered with ‘Bavires’, while some individuals showed profiles strongly associated with methyl chavicol, even exceeding that of ‘Tulsi’. A moderate negative correlation was found for 1,8‑cineole and β‑pinene, while 18 and 50 compounds showed only low or no correlations with 2C DNA content and chromosome number, respectively. Our results demonstrate that hybridizing O. basilicum var. basilicum with O. tenuiflorum is well-suited for introgression breeding, and that Genovese-type basil characteristics like scent can be restored through successive backcrosses.