Investigation of Chilling Effects on Characteristics of Seed Germination, Vigor and Seedling Growth of Nepeta spp. Species

To study the effects of chilling on dormancy breaking and the increased germination characteristics of Nepeta (germination percent and speed, seedling length, vigor index, wet and dry weight), a factorial experiment in a completely randomized design with 4 replications was implemented in a laboratory in 2014. Factor A was the chilling treatment in three levels (control, one-month and two-month pre-chilling of wet seeds at 4°C) and factor B was related to the seeds of 10 different species of genus Nepeta. After chilling, seeds of control were placed in a germinator for 15 days at 20°C and light-to-dark cycle of 16 hours light (1000 lux) to 8 hours dark. The results showed that chilling treatments had significant effects (p<0.01) on germination percent, germination speed, vigor index and fresh weight, but they had no effects on the seedling length. The chilling effects on germination percent showed that one-month chilling had a positive effect on N. haussknechtii with 40% and N. menthoides with 36.5% and two-month chilling had a positive effect on N. haussknechtii with 43%. The two-month chilling effect on germination speed was positive for most species. Generally, one-month chilling had positive effects on the increased seed vigor index of N. betonicifolia, N. haussknechtii and N. menthoidesand by 20.48%, 25.33% and 17.99%, respectively as compared to that of control treatment and two-month chilling had positive effects on the increased fresh weight of N. cataria, N. haussknechtii, N. pungens, N. menthoides andN. crassifolia.