Abstract:

Aims Juglans regia and J. sigillata are important economic nut trees and are widespread in Sichuan Province. Accurate evaluation of genetic diversity and relationships between species is essential for effective preservation of germplasm resources and breeding. Traditional methods for assessment of genetic diversity in walnut, based on morphological, physiological and biochemical studies such as isozyme analysis or RAPD makers, are sensitive to environment so results are not reliable. AFLP has been applied extensively and effectively in population molecular ecology research and population genetic studies. Our aims were to identify genetic structure among populations and to examine genetic relationships between the two species.

Methods We compared three wild J. regiapopulations occurring at Qingba Mountain, Daduhe Valley, and southern Ganzhi District in Sichuan Province, and one wild J. sigillatapopulation at Panzhihua District in southeastern Sichuan Province. We selected 46 samples to analyze by AFLP molecular maker technology using 4 pairs of primer combinations screened.

Important findings We obtained 244 bands including 146 polymorphic bands. The percentage of polymorphic bands (P) was 59.84%. For the J. sigillatapopulation, percentage of polymorphic bands (P) was 52.05%, effective number of alleles per locus (A_e) was 1.339 9, and Nei’s gene diversity index (H) was 0.196 1, Shannon’s information index (I) was 0.289 8. For J. regiapopulations at species level, estimates were P=55.33%, A_e=1.322 9, H=0.190 8, andI=0.286 3. Although these findings showed that genetic diversity of J. sigillatawas slightly higher than the other species, genetic diversity level was generally equivalent. Shannon information index, Nei’s genetic diversity coefficient and analysis of molecular variance showed that 85.64%, 87.4%, 88.93% genetic diversities, respectively, distributed within populations at the species level. Most variation (80.65%) consistently originated from the interior of groups. The population ofJ. sigillatapossessed the greatest amount of unique bands, accounting for 4.5% of the total amplified bands, which indicated genetic variation between two species. The genetic differentiation coefficient (G_st=0.093 5) between two species is very low. Juglans regiashowed high genetic affinity to J. sigillata.Nei’s Genetic distances between populations varied from 0.038 2 to 0.069 2 and genetic similarities ranged from 0.933 2 to 0.962 5, which indicated there were high similarities among populations. UPGMA analysis revealed that threeJ. regiapopulations clustered first, and genetic distance was closest between the Daduhe Valley and southern Ganzhi District populations.

Key words: walnut, Juglans regia, Juglans sigillata, AFLP, genetic diversity, population, genetic structure