Genetic Diversity of Hippophae rhamnoides Populations at Varying Altitudes in the Wolong Natural Reserve of China as Revealed by ISSR Markers

Hippophae rhamnoides L., a dioecious and deciduous shrub species, occupies a wide range of habitats in the Wolong Nature Reserve, Southwest China. Our present study investigated the pattern of genetic variation and differentiation among five natural populations of H. rhamnoides, occurring along an altitudinal gradient that varied from 1,800 to 3,400 m above sea level in the Wolong Natural Reserve, by using ISSR markers. Based on fingerprinting patterns generated by fifteen primers, high levels of genetic variation were present within populations and subpopulations. Substantial genetic divergence was observed among populations, and also among female and male subpopulations, the G_ST values equaling 0.182, 0.222, and 0.238, respectively. Such considerable divergence present among populations and subpopulations may be caused by complex topography which effectively restricts gene flow, and by variable climatic conditions at different altitudes which may cause varying selective pressures. A significantly positive correlation between genetic and altitudinal distances was detected for the five populations and female subpopulations of H. rhamnoides. The cluster analysis including all populations or male subpopulations resulted in three altitude groups. Our results suggest that altitudinal gradients may be the prime cause affecting the genetic variation pattern of different populations and subpopulations in H. rhamnoides in the Wolong Nature Reserve, Southwest China.