Patterns of pollen stainability in polyploids of the genus Onosma (Boraginaceae)

Abstract

Background and aims -The genus Onosma (Boraginaceae) is a taxonomically and phylogenetically very complex plant group, with several taxa of hybrid or polyploid origin. An extensive pollen viability survey within the genus could help to solve some evolutionary or taxonomic incertainties within the genus, but it has never been performed. The aim of the present study is to determine the degree of pollen viability of selected species of various ploidy levels and to investigate if microevolutionary processes, such as polyploidization and hybridization, are associated with variation in pollen viability. Methods -Pollen staining with lactophenol blue was chosen as an indirect method for determining pollen viability. Ploidy level information was obtained from an extensive literature search. In mixed populations, the ploidy level of individuals was determined based on flow cytometry screening. Key results -Considerable variation in pollen stainability is present among taxa of Onosma. Pollen stainability is high in most diploids (72-98% in mean), allotetraploids (90%) and allohexaploids (97%), but lower in autotetraploids (71%) and allotriploids (2-49%). At the population level, considerable variation in pollen stainability was found in the allotriploid O. arenaria (14-83%), while the taxonomically related allotetraploid O. pseudoarenaria is less variable (71-99%). Conclusion -This study shows the value of the staining method in the study of the genus Onosma. Low pollen stainability appears to be associated with autopolyploidization as well as recent hybridization processes suggesting the presence of microsporogenesis or microgametogenesis abnormalities. In contrast, pollen stainability is high in stabilized allopolyploids indicating proper meiosis with maintenance of homologous pairing of parental chromosomes and correct pollen development.

Spatial and Ecological Drivers of Genetic Structure in Greek Populations of Alkanna tinctoria (Boraginaceae), a Polyploid Medicinal Herb

“…In tribe Lithospermae, several tetraploid species have been identified (Luque, 1990;Korbecka et al, 2003;Coppi et al, 2006;Kolarčik et al, 2014;Weigend et al, 2016). Moreover, both allopolyploids and autopolyploids have been described in this tribe (Luque and Valdes, 1984;Kolarčik et al, 2014Kolarčik et al, , 2015Weigend et al, 2016). In the present study, two lines of genomic evidence led us to suggest that A. tinctoria might be an autopolyploid.…”

Nuclear genome size variation in the allopolyploidOnosma arenaria–O. pseudoarenariaspecies group: methodological issues and revised data

“…Although a thorough examination of genome size may elucidate several evolutionary or taxonomic issues within the Onosma genus, the DNA content has been determined in very few taxa (eight taxa in four different studies, Mártonfi et al 2008;Siljak-Yakovlev et al D r a f t 2010; Kolarčik et al 2014;Kolarčik et al 2015). However, although high variability has been observed even within single species, we can not exclude the possibility that this variation could be an artefact caused by methodological errors.…”

“…Moreover, the genus also contains certain allopolyploid taxa that combine at least two genomes of different basic numbers. Although the basic phylogenetic relationships among taxa of the genus have yet to be clarified, D r a f t hybridization and polyploidization seem to be important forces promoting genus differentiation (Kolarčik et al 2010(Kolarčik et al , 2014(Kolarčik et al , 2015. This is exemplified in Europe by one of three infrageneric groups, Heterotricha.…”

Two new species and a new record for Onosma L. (Boraginaceae) from northwestern Iran

“…Recent molecular studies do not support the monophyly of Boissier's three sections (Kolarčik et al, 2010;Cecchi et al, 2011Cecchi et al, , 2016 but they remain useful as convenient informal groups for the purpose of identification (Peruzzi and Passalacqua, 2008;Cecchi et al, 2016). Kolarčik et al (2010Kolarčik et al ( , 2015 considered O. subsect. Heterotricha as an evolutionarily intermediate lineage which probably originated by hybridization.…”