| Oaks, belonging to Quercus Fagaceae, typical tree species with wind-pollination and outcrossing features. Due to their sympatric distribution patterns, Oaks were considered to have strong interspecific gene exchange, and serve as model plants for studying genetic diversity, speciation and evolutionary processes, as well as interspecific introgression and hybridization. China was assumed to be the origin area and one of the modern distribution centers of Quercus, where oaks are the types of trees possessing great economic and ecologic importance. This research targets at the sympatric populations of Quercus acutissima, Q. variabilis, Q.fabri and Q. glandulifera var. brevipetiolata from four sample plots in Jiangsu and Anhui Province and analyzes their genetic structure as well as genetic variation of populations and individuals in order to ascertain oak’s interspecific introgression and hybridization status. Main research results were as follows:(1) Phenotypic traits variation of these four species of Quercus. At the intraspecific population level of Q. acutissima significant variations occurred on number of lateral vein pairs and petiole length. All phenotypic characters except petiole length of Q. fabri had significant variations. Populations of Q. glandulifera var. brevipetiolata were found to be significantly variable on leaf length, ratio of leaf length and width and number of lateral vein pairs. No significant variations were investigated on any characters of Q. variabilis. Clustering analysis showed that there existed phenotypic traits variation within populations of the four species of Quercus. Some individuals of Q. fabri, Q. acutissima and Q. variabilis showed obvious interspecific phenotype traits.(2) Variation of nuclear genome size. By comparing four traditional nuclear isolation buffers, the method of orthogonal design was applied to improve the classic Marie’s buffer. Nuclear genome sizes of 120 individuals from ZJ plot in Jiangsu province has been estimated through flow cytometry. Results showed that significant variations on nuclear genome size existed between populations of Q. acutissima vs Q. variabilis, Q. acutissima vs Q. fabri, Q. acutissima vs Q. glandulifera var. brevipetiolata, Q. variabilis vs Q. fabri, Q. variabilis vs Q. glandulifera var. brevipetiolata. No significant variations were found between populations of Q. fabri and Q. glandulifera var. brevipetiolata. Clustering results indicated that extensive interspecific variation occurred within section and only some interspecific individuals were found across sections.(3) Genetic structure of populations.27 in 92 nSSR primers developed for related species have been selected and amplified successfully in the four species of Quercus. Then PCR reaction was carried out on 300 DNA samples. Afterwards genetic diversity analysis was conducted at overall four species, single species and population levels. At overall species level,27 of SSR primers detected 526 alleles, with an average of 19.48, and expected heterozygosity (He) were 0.79-0.94 (with an average value of 0.90), polymorphism information content index (PIC) 0.755-0.939 (average 0.886). These parameters showed that the genetic diversity was high. At the species level, the genetic parameters were 13.63-14.48 for average number of alleles,0.84-0.87 for expected heterozygosity (He),0.811-0.845 for polymorphism information content (PIC). The data showed a higher level of genetic diversity, which was topped in Q. acutissima, followed by Q. fabri, Q. variabilis, and Q. glandulifera var. brevipetiolata owned the lowest genetic diversity. Analysis of 10 oak populations indicated that all populations showed high levels of genetic diversity.(4) Genetic variation of population, i For a species, genetic variation rate within population was 83%-91%, variation rate among populations was 9%-17%, gene flow (Nm) was 1.202-2.394. Among all populations, the highest variation rate appeared between populations of Q. glandulifera var. brevipetiolata in LT plot in Anhui province (LT-B) and population of Q. glandulifera var. brevipetiolata in ZJ plot in Jiangsu province (ZJ-B), the lowest variation rate between populations of Q. acutissima. ii Across species, gene flow (Nm) among populations were 1.015-4.267, genetic variation rates within population 80%-94%, variation rates among populations 20%-6%. Populations of Q. acutissima and Q. variabilis, populations of Q. fabri and Q. glandulifera var. brevipetiolata possessed strong genetic exchanges with relatively low inter-population genetic variation rates (6%-13%). Gene flows (Nm) among other interspecific populations were relatively low and variation rates among populations were 14%-20%. iii Clustering results revealed that obvious differentiation and interspecific variation occured within populations of Q. fabri and within populations of Q. glandulifera var. brevipetiolata and species differences are minimized. Some individuals showed a higher degree of interspecific variation. Population of Q. fabri in ZJ plot (ZJ-F) showed a strong variation towards Q. glandulifera var. brevipetiolata, ZJ-F and ZJ-B samples constructed a potential introgressive population with high incidence.(5) Interspecific introgression.24 individuals (6.67%) of introgression were detected from 300 sampies. Among them, one individual was suspected to be hybrid F1. Interspecific introgressions were concentrated in Q. acutissima-Q. variabilis, Q. fabri-Q. glandulifera var. brevipetiolata, Q. variabilis-Q. glandulifera var. brevipetiolata. Q. fabri-Q. glandulifera var. brevipetiolata possessing the greatest proportion (10.83%), while the lowest percentage (1.71%) occurred between Q. variabilis-Q. glandulifera var. brevipetiolata. No individuals of introgression was detected in Q. acutissima-Q. fabri, Q. acutissima-Q. glandulifera var. brevipetiolata, Q. variabilis-Q. fabri. Results demonstrated that the phenomenon of introgression prevailed within section and can occur among section, but not a common phenomenon. |
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