Variation in Nuclear DNA Content and Chromosome Number among and within Caladium Species

Cultivated caladiums (Caladium ×hortulanum) are a major floriculture crop in the United States, especially in the southern and southeastern states.  Genetic improvement of cultivated caladiums has been primarily through hybridization among existing cultivars.  To broaden the genetic base of cultivated caladiums and/or introduce biotic and/or abiotic stress tolerance traits may necessitate more interspecific hybridizations with other caladium species.  In addition, the number of species in the genus Caladium is still a matter of discussion.  Plant taxonomists have divided the genus into seven to 17 species.  The main debate is about the classification of Caladium bicolor, Caladium marmoratum, and Caladium picturatum, and the status of Caladium ×hortulanum.  The present study was undertaken to determine the variation in nuclear DNA content among and within nine caladium species and chromosome number of four caladium species.  Flow cytometric analysis revealed significant variation in nuclear DNA content among species, ranging from 2n = 2.98 pg in Caladium lindenii to 2n = 9.89 pg in C. ×hortulanum cv. Chang Suek.  Significant variation was also observed within certain species, such as Caladium steudneriifolium.  All four caladium cultivars examined have 2n = 2x = 30 chromosomes.  Lower somatic chromosome numbers were observed in some caladium species.  Results from this study have provided new insights into the relationships among and within caladium species and shed light on the origin of cultivated caladiums. The available information will be also very valuable for designing sexual crosses for caladium breeding.