Contribution to the knowledge of genome size variation in Calendula L. (Asteraceae) with special focus on the SW Mediterranean region

Abstract

Calendula is one of the most taxonomically complex genera within the Asteraceae family due to hybridization, polyploidization events, and production of a highly variable morphology of the achenes. Considering the complexity of Calendula, this study was conducted to extend the understanding of the relationships between SW Mediterranean taxa, and assess the relationships between genome size and chromosome number, ploidy level and life cycle in 77 populations covering 14 taxa. Genome size estimations are provided for the first time for five species and for three putative new undescribed species. Mean 2C values differed up to 6-fold among different euploid species (from 1.37 pg in diploid to 8.26 pg in octoploid populations). 1Cx-values varied 2.07-fold (between 0.68 pg and 1.41 pg). Mean 1Cx genome size revealed significant differences between different ploidy levels. Genome size variation is a significant factor for explaining the relationships within Calendula, and individuals not fitting the current classification were found and should be analysed in detail in future studies.

Keywords:

• Calenduleae
• chromosome numbers
• Compositae
• hybridization
• nuclear DNA content
• 2C
• 1Cx

Acknowledgements

We thank anonymous reviewers for the suggestions, and William Smith for the English revision, that greatly improved the manuscript. Thanks are also due to several herbaria (ABH, AL (ENSA), ARAN, B, BC (IBB), BCN, BM, BONN, BR, C, COI, E, ELVE, FI, G, GAT, GDA (GDAC), HAL, JACA, JAEN, JE, K, LD, LEB, LISI, M, MA, MACB, MAF, MARK, MGC, MPU, O, P, PO, RAB, RNG, SALA, SANT, SEV, TFMC, US, VAL and W) for allowing the study or loaning plant material of Calendula. We are very grateful to several institutions that have authorized collections of Calendula specimens, namely: Instituto da Conservação da Natureza e das Florestas (Portugal), Parque Nacional de las Islas Atlanticas de Galicia y Parque Natural de la Sierra de las Nieves (Spain), Jbilet Reserve (Morocco). We also thank for the achene samples provided by: Real Jardín Botanico de Madrid (CSIC), USDA, IPGN, Olofron Plume (Cornell University, Ithaca, United States), Stephen Mifsud (Malta) and Miguel Sequeira (Univ. of Madeira, Portugal).

Disclosure statement

The authors declare that they have no conflict of interest.

Additional information

Funding

This study was partly funded by the Portuguese Foundation for Science and Technology and UNESCO Fund for financing the work of ACG with the scholarship SFRH/BD/51464/2011 and in the form of institutional resources provided by the FCT/MCTES for the financial support to CESAM (UIDP/50017/2020 + UIDB/50017/2020 + LA/P/0094/2020), through national funds. This research was also supported by POPH/FSE funds by the Portuguese Foundation for Science and Technology (FCT) to the LEAF (Linking Landscape, Environment, Agriculture and Food research Unit – UID/AGR/04129/2013), and with a starting grant to SC (IF/01267/2013), and Portuguese Foundation for Science and Technology and European Social Fund financed the work of HO with the scholarship SFRH/BPD/111736/2015. Additional support was provided by SYNTHESYS, grant GB-TAF-2900, to PS, allowing the study of BM and K’s Calendula collections.