In vitro induction of tetraploids in the ornamental plant Melastoma candidum using colchicine treatment

Abstract

Artificially inducing tetraploids can aid in breeding new acarpous varieties and distant hybridization. This study firstly achieved polyploid induction in Melastoma, a popular ornamental shrub in southern China and northern Vietnam. The mature tetraploid obtained was identified and characterized. Colchicine was used as a mutagenic agent for doubling of germinating seed explants. By in vitro method, survival rate and tetraploid rate were affected by pre-culture, chemical concentration, and exposure duration. Explants treated with 0.2% concentration for four or more days showed 100% polyploid induction based on radicle morphology. However, considering induction success and mortality, the best option was 0.2% concentration for two days, resulting in a 71.9% polyploidization rate and 71.7% survival rate. Plantlets were then inoculated on MS + 0.5 mg/L BA + 0.1 mg/L NAA for shoot induction and ½ MS + 0.5 g/L NAA for further rooting. Twelve mature tetraploid plantlets were finally confirmed by flow cytometry. Phenotypic analysis revealed smaller, rounder, and thicker leaves with more abundant and longer epidermal hairs in polyploid and mixoploid plants compared to diploids. Also, stomata of polyploid were larger and sparser than those of the diploid wild type. These findings unprecedentedly provided an effective methodology for artificial polypoidy germplasm resources acquisition within Melastomataceae, which lay an important foundation for breeding fruitless cultivars.