Ploidy Identification by Flow Cytometry and Application of the Method to Characterize Seasonal Ploidy Variation of Wild Populations of the Red Alga Gracilariopsis lemaneiformis

Gracilariopsis lemaneiformis (Gp. lemaneiformis) is an economically important alga. At present, there is no way to quickly and easily determine its ploidy and life cycle dynamics in wild populations, which affects the process of genetic breeding. In this study, we developed and verified a ploidy identification method using flow cytometry and then used it to explore the seasonal fluctuation of the ploidy ratio and the environmental factors that influence it in wild populations of this species. Of the three methods we tested for nucleus extraction, quick chopping was the best because of its high extraction efficiency, low debris background, obvious subcellular scatter plot, and clear typical histogram. Samples from the tip of the alga were more suitable for preparing the nuclear suspension than samples from the base. Generalized linear model analysis based on diagnosis of multicollinearity revealed a negative correlation between temperature and ploidy ratio. Among the environmental factors tested, temperature had the greatest influence on the ploidy ratio, whereas precipitation and sunshine duration had no effect on the ploidy ratio fluctuation. Our study will be useful for material collection and studies of utilization and life cycle dynamics. Moreover, understanding of ploidy dynamics may provide a theoretical basis for improving variety and breeding of Gp. lemaneiformis in the future.