Impact of temperature on karyotype differences in Cynodon dactylon of different ploidy levels at different latitudes

Chromosomal karyotype is closely linked to species evolution, adaptability, and environmental responses. As global climate change intensifies, temperature fluctuations critically affect chromosomal behavior, consequently influencing plant growth and development. However, the patterns of karyotypic variation that underpin ploidy levels evolution in Cynodon dactylon (L.) Pers. remain poorly understood.

In this study, we selected 42 individuals of C. dactylon from 13 regions and cultivated them under three temperature conditions (25℃, 30℃ and 35℃). Their ploidy levels encompassed diploid to hexaploid. This research investigated the effect of temperature changes on karyotypes of C. dactylon. We employed microscopic and karyotype analysis to examine populations at different ploidy levels along latitudinal gradients in China. Statistical methods comprised preliminary analyses (ANOVA with Games-Howell and Tukey HSD post-hoc, PCA, correlation) and advanced modeling (mixed-effects and logistic regression), all preceded by assumption checks.

Karyotype asymmetry varied with ploidy level. Diploids possessed the most asymmetric karyotypes, characterized by a higher coefficient of variation for chromosome length (CV_CL) compared to polyploids. Among polyploids, tetraploids exhibited the most symmetric karyotypes. Centromeric positions remained stable across all karyotypes. Inter-individual variation was primarily driven by both temperature and ploidy level. The temperature decreased from 30℃ to 25℃ triggered a karyotype shift (1A to 1B), primarily in diploids, by altering chromosome structure and meiosis. Diploids exhibiting chromosome length variation were mainly distributed in high-latitude regions, where their karyotypes exhibited heightened sensitivity to temperature fluctuations between 25℃ and 35℃.

Diploids were more susceptible to temperature fluctuations due to their highly asymmetrical karyotypes. Conversely, tetraploids were less affected by temperature variation, which was associated with their symmetrical karyotypes. The karyotypic symmetry of higher ploidy levels underpinned the greater stability of polyploids under temperature variation. Temperature changes along latitudinal gradients influenced karyotype changes in C. dactylon, and karyotype evolution was pivotal in polyploid formation. These findings provide a theoretical basis for understanding the ploidy evolution of C. dactylon, screening wild resources in response to climate changes, and breeding new varieties.