Genetic variation of Laminaria japonica (Phaeophyta) populations in China as revealed by RAPD markers

For the population genetics analysis of the naturally grown brown seaweed Laminaria japonica (Laminariales, Phaeophyta) sampled from Dalian, Yantai, Weihai, Rongcheng and Qingdao in China, ten primers were employed to produce 88 bands as revealed by randomly amplified polymorphic DNA (RAPD) markers, and all these bands were polymorphic. According to these band patterns, there were 94 distinct phenotypes occurred in 100 samples indicating the high heterozygosity of this kelp. Dalian population samples showed the highest percentage of polymorphism (71.67%), and also the higher diversity estimated on the basis of the Shannon's index (8.498), suggesting that this population could be chosen as the best resource for genetic breeding. The highest diversity of Yantai population possibly resulted from the introduction of L. longissima used for interspecific cross breeding with L. japonica cultivated in China. From Dalian southwards to Qingdao, the genetic variation of the five populations became less with a decrease in latitude, possibly due to the natural selection especially of high temperature. The genetic distance (Φ_ST values) of the five populations was a little significantly correlated with the geographical distance (r=0.496) at P=0.05 by Mantel's test. Weihai, Rongcheng and Yantai populations were closely grouped genetically together by Neighbor-joining cluster analysis probably in that the dispersal of the kelp by propagules more easily occurring in the range of relatively short distance. The analysis of molecular variance (AMOVA) also demonstrated that the relatively higher variation occurred among populations (71.49%) at an extremely significant level (P <0.000 1). All these evidence showed that there was a relatively distinct genetic differentiation among the sampled kelp populations, and L. japonica grown in China was also rather heterozygous in heredity.