Induction and characterization of polyploids through morpho-anatomical, cytological, chemotypic, and molecular approaches in Patchouli (Pogostemon cablin Benth.)

Patchouli (Pogostemon cablin), is an industrially important aromatic plant that produces patchouli oil. The present experiment aimed to generate polyploid plants of patchouli with increased herb yield, oil production, and higher patchouli alcohol content. In the present study, colchicine, a chemical compound known to induce polyploidy was used at concentrations of 0.2% and 0.3% for 48 h. The diploid variety CIM-Shrestha (2n = 2X = 32) was used as the starting point. Polyploidy was successfully induced in vitro conditions and confirmed through various analyses including chromosome counting, anatomical, morphological, and gene expression studies. Treating the diploid callus with 0.2% colchicine resulted in viable and stable tetraploid seedlings. These tetraploids had a chromosomal count of 2n = 4x = 64. Tetraploids exhibited distinct morphological, anatomical, and chemical characteristics, such as thicker leaves, more oil glands, higher chloroplast numbers, larger stomata size, patchouli alcohol, and α-Guaiene. In field conditions, the induced tetraploids remained stable and the majority of tetraploid lines showed higher oil content and patchouli alcohol concentrations compared to diploid plants, although herb yield was lower in tetraploids. In the gene expression study, five (PcHMGR, PcFPPS, PcTPSCF2, PcTPSB15, and PcPTS, along with the expression of the control gene Pc18S) pathway genes related to the patchouli alcohol production pathway were studied. The Real Time-qPCR results show that there was no significant change in the expression of any of the five analyzed genes.