Morphological, cytogenetic and molecular characterization of new somaclonal variants in four caladium (<i>Caladium</i> × <i>hortulanum</i>) cultivars

Abstract

The discovery of triploids in caladium has raised strong interest in their use in cultivar development. For triploid production, tetraploids must first be generated from elite breeding material without the introduction of deleterious alleles like has been seen with chemical agents like colchicine and 2,4-D. To meet this new demand, virus eradicated, meristem-tip caladium cultures were grown on auxin-free media and used for generation and evaluation of new somaclonal variants. Over 12,000 micropropagated caladiums were visually screened <italic>ex vitro</italic> for sports varying from the wild-type phenotype. Eight variants from four cultivars were discovered and characterized for morphological, cytological, and molecular changes. Genome duplication occurred in seven of the variants with an average nuclear DNA content of 18.76 pg·2C⁻¹. The tetraploid variant of cultivar ‘White Wing’ had eight more chromosomes (2<italic>n</italic> = 4<italic>x</italic> = 68) than the other tetraploids and exactly double that of its wildtype. All other diploids had the expected 2<italic>n</italic> = 2<italic>x</italic> = 30 chromosomes and tetraploids recorded 2<italic>n</italic> = 4<italic>x</italic> = 60. Tetraploids had 19% rounder leaves and 44% thicker leaves than the diploids in the study. Tetraploids also had a 49% and 31% increase in stomata length and width, respectively. Molecular marker analysis only revealed two polymorphisms with both occurring in the 'White Wing' variant. Few changes in molecular marker banding could indicate that the tetraploids discovered have a clean duplication of the genome and might effectively be used for new triploid cultivar development.