Hidden diversity in wild Beta taxa from Portugal: insights from genome size and ploidy level estimations using flow cytometry

Crop wild relatives constitute a broad pool of potentially useful genetic resources for plant breeders. The genus Beta L. (Amaranthaceae) is an important source of crops, primarily for sugar production. Until recently, species within Section Beta were mostly cytogenetically uniform, with diploidy being prevalent. Still, with the discovery of tetraploid individuals of the wild B. macrocarpa in the Canary Islands, a large-scale study was necessary to evaluate the cytogenetic diversity within the wild Beta. For that, genome size and ploidy level of B. vulgaris subsp. maritima and B. macrocarpa from 21 populations across Portugal mainland and islands, including all know populations of the later taxon, were estimated using propidium iodide flow cytometry. This work revealed a cytogenetically diverse scenario. The analyzed populations were mostly diploid, except for one population of B. vulgaris subsp. maritima that presented both diploid and tetraploid individuals, and for two populations of B. macrocarpa where two or three cytotypes (diploids, tetraploids and/or hexaploids) were found. The nuclear DNA content of diploid individuals was estimated as 1.44±0.035 and 1.41±0.027 pg/2C for B. vulgaris subsp. maritima and B. macrocarpa, respectively. Also, leaves of both species presented variable levels of endopolyploidy. The obtained results are discussed within the context of interspecific hybridization and cryptic diversity and constitute significant data for the conservation of these wild Beta crop relatives.