Genetic assessment of plant material for studies of the genetic causes to female biased sex ratios in Salix viminalis L.

Abstract: Biased sex ratios are highly common among dioecious plants. Salix viminalis is a dioecious tree or a woody shrub that has an overall female biased sex ratio. Most likely the bias is initiated in an early stage of development either by abortion of certain male zygotes or by genetic incompatibility leading to failure of fusion between the sperm and the egg. Salix viminalis has a female heterogametic or ZW sexual system, where the W represents a female-specific chromosome or region, meaning that all female offspring has one maternally inherited haplotype. In this work, I designed primers for markers located in the sex determination region on chromosome 15. By changing different parameters of PCR and by analysing the sequences of all the individuals, the expected genotypes of the used individuals were confirmed. Thus, in the further studies the markers can be applied in offspring and their genotypes can be determined, in order to estimate the sex ratio. Moreover, a germination test of different crosses of two populations of S. viminalis was done. One population had even sex ratio and other one female biased sex ratio. By comparing the germination rates between the crosses, the effect of inbreeding on germination rates in each cross was studied. Furthermore, based on the germination test the relatedness between homozygosity and white seeds phenomena was studied, since we assume that white seeds have homozygous genotype. In addition, the data which included germination rates was analysed in JMP program using ANOVA test. The results indicate that the reasons that some PCR programs in this study gave better results using the same primers than the others may be formation of primer dimers, secondary structures and that the sex determination region has many repetitions. The results show that there is significant difference between the germination rates between the crosses and between the catkins of each cross. Based on assumptions, in this work it is suggested that white seeds may not present homozygous individuals. Moreover, homozygosity may be related also to the black seeds or the homozygous seeds might not be even fully formed. Furthermore, it is possible that genetic incompatibility between homozygous allelic combinations have led to the differences among the germination rates of the crosses. In the further studies of the white seeds phenomena, sequencing of the genomes of the seeds is required in order to investigate the relatedness between homozygosity and white seeds.