Limonium homoploid and heteroploid intra- and interspecific crosses unveil seed anomalies and neopolyploidy related to sexual and/or apomictic reproduction

Apomixis is a form of asexual reproduction that consists in cloning through seeds. In Limonium (Plumbaginaceae) species present a pollen–stigma dimorphism linked to a sporophytic self-incompatibility system associated with sexual and/or apomictic reproductive modes. Previous work in other genera suggests that the emergence of apomixis is associated with hybridization and/or polyploidy. In this study, our goal was to test the ability of diploid and tetraploid species to hybridize and to evaluate the variate outcomes from these crosses. To achieve this, sexual diploid (L. nydeggeri, L. ovalifolium) and facultative apomict tetraploid (L. binervosum, L. dodartii) plants from cultivated material, previously cytogenetically and reproductively characterized, were used for experimental intra- and interspecific crosses. Genome sizes, ploidy levels and morphology were examined in the resulting progenies. Results showed a high production of viable seeds in particular in plants from tetraploid × diploid (heteroploid) crosses. In these crosses, some seedlings exhibited pleiocotyly (tricotyl, tetracotyl), while others showed polyembryony. In both homoploid (diploid × diploid) and heteroploid (tetraploid × diploid) crosses, most of the offspring plants were morphologically and in their ploidy similar to the female receiver, although some morphological abnormalities were found. Molecular progeny tests using the nrDNA ITS1-ITS2 sequence demonstrated an astounding range of diploid offspring plants originated from diploid × diploid crosses that were either genetically similar or distinct from parental plants. Although in intraspecific crosses most of the resulting progeny was diploid, one triploid plant was formed. Moreover, in homoploid interspecific crosses, neopolyploids (two tetraploid plants) were produced. Progeny plants from heteroploid crosses always showed nrDNA ITS1-ITS2 sequences identical to the parental plant used as female receiver. In conclusion, diploid homoploid crosses presented genetically diverse offspring arising from sexual reproduction. By contrast, heteroploid crosses generated clonal, maternal (apomictic) offspring.