Genetic Diversity And Coevolutionary Analysis Of Armillaria Mellea Associated With Gastrodia Elata In Western Hubei Province

Abstract Reciprocal phenotypic change may arise from back-and-force interaction of the species in symbiotic relations or host-parasite pair. Besides, adaptive phenotypic plasticity can occur in fluctuating environment. Therefor, analysis about adaptive phenotypic variance is important for better understanding of flexibility in changeable environment and coevolutionary mechanism between the interactive species. Among many orchid-mycorrhizal fungi pair, Gastrodia elata - Armillaria mellea symbiont was studied in this text for the special relation between them. Using sampling strategy of one A.mellea individual mapping to another G. elata unit, phenotypic diversity of 6 qualitative characters and 6 quantitative characters of 90 A.mellea individuals were observed , which associated with three different G. elata forms in 7 divisions of the Three-Gorge reservoir area in Hubei province. Totally 25 morphological groups of A.mellea were described based on traits of the 6 qualitative characters. A.mellea groups coexisted with different G.elata forms were of distinct main morphology types and peculiar ones. The phenotypic diversity level of the total Armillaria mellea group was high (H_mt=3.009; H=0.9712). Phenotypic diversity level of the populations of the 7 divisions varies by a wider margin(H_mt:1.242-2.607; H: 0.4736-0.9249) than which of the groups coexisted with different G.elata forms(H_mt: 2.395-2.61; H: 0.7723-0.930), and phenotypic differentiation among populations of the 7 divisions was obvious. Variance analysis revealed signifiant phenotypic variance of A.mellea group classified by environment gradients, and there was significantly obvious correlation between phenotypic variance of these groups and environmental factors. Also, there was signifiantly phenotypic variance among the A.mellea group coexisted with different G.elata forms , and significantly obvious correlation between phenotypic variance of the three groups and environmental factors. Clustering analysis showed that A.mellea individuals were not clustered by distinct divisions of the sampling area, nor by G.elata forms in symbiosis . However, the A.mellea individuals of the same morphological types were grouped together. Further analysis results showed that the high phenotypic diversity of A.mellea group associated with G.elata may have resulted both from its long-term interaction with more other species and effects of fluctuating environment, consequently make the A.mellea group have the properties of adaptive phenotypic plasticity in complex and changeable environment. Compared to other environmental factors, such as longtitude, latitude ,and soil type, the effects of altitude gradients on phenotypic variance of A.mellea was weaker, indicating frequent gene flow of less geography isolation may weaken the adaptive phenotypic differentiation. The remarkable tendency of different G. elata forms toward A.mellea groups of different phenotypic variance may arised from the asymmetrical interacting effects of the two species, indicating the existence of asymmetrical coevolutionary relation between G.elata and A.mellea.The genetic polymorphisms and genetic differentiation of the 7 Armillaria mellea populations in Three-Gorge reservoir area, including 90 individuals, were analyzed using inter-simple sequence repeats (ISSR) markers. Totally 169 bands were obtained using 6 ISSR primers, of which 167 bands were polymorphic. At species level, Nei's diversity index (H) and Shannon's diversity index(I) were 0.3362 and 0.4976, respectively. The genetic diversity level of WF populaton was higher than other populations. Genetic differentiation coefficient and gene flow value among 7 populations was 0.1863(Gst) and 2.1838, respectively. Mantel test showed weak correlation between genetic and geographic distances among 7 populations(r=0.09413, P=0.8292), not closing to the 'Isolation-by-distance Model'. In addition to high level of intraspecific diversity, 81.37% genetic differentiation within the populations , indicated that reproduction in Armillaria mellea which coexisted with Gastrodia elata in Three-Gorge reservoir area cannot be exclusively colonal. ISSR markers indicated very little molecular variance among the three Armillaria mellea groups which associated with different kinds of Gastrodia elata forms (Gst=0.0299) , suggesting weak effects of Gastrodia elata forms on Armillaria mellea 's genetic differentiation .We also compared the results from two methods, i.e. ISSR markers and phenotypic variance analysis , which revealed different parts of genosome of Armillaria mellea and the results they revealed complemented each other.