Optimization of chromosome preparation and karyotype analysis of Panicum repens

In order to explore the optimal approach for analyzing the root tips of Panicum repens, we compared different pre-treatment, fixation, prehypotension, and dissociation conditions during chromosome preparation. The results demonstrated that the optimal pre-treatment was a mixture of ice and water at 4 ℃ for 22 h, the optimal fixation was Cano′s fixed liquid Ⅰ at 4 ℃ for 24 h, the optimal pre-hypotension was 0.075 mol·L⁻¹ KCl at 25 ℃ for 15～20 min, and the optimal dissociation was a mixture of 1% pectinase and 2% cellulase at 25 ℃ for 3 h. The karyotype analysis revealed the formula for P. repens to be 2n = 2x = 40 = 34m + 6sm. Furthermore, no satellite was observed. The absolute chromosome length ranged from 10.87 to 19.21 μm, which indicates P. repens contains a single large chromosome. The relative chromosome length composition was 2n = 40 = 2L + 16M₂ + 22M₁. The ratio of longest to shortest chromosome length was 1.77, and the arm ratio ranged from 1.04 to 2.08. The karyotype asymmetry coefficient was 58.99%, and the karyotype beingwas 2A, which may be an evolutionarily primitive type, providing a certain theoretical and technical basis for the origin, evolution, inheritance, and breeding of P. repens.