| O. fragrans is a traditional population flower in China and is generally applied in the gardensdue to its abundant cultivars and rich variation of floral trait. Its sexual system is typicalandrodioecy. Wild resources with rich variations are the important resources of parentalgermplasm innovation. However, excessive development and serious damage of wild resources ofO. fragrans result in the loss of suitable habitat at present, which leads to rapid decrease ofdistribution range, population size and populations, so that protection is took urgently for O.fragrans. In the present study, wild O.fragrans and important cultivars were analysed from threeaspects of floral trait changing, flower bud differentiation and genetic diversity to illustrate theevolution and development model of pistil in hermaphrodites or pistillode in males and discuss theevolution model of androdioecy in plant. Meanwhile, the genetic diversity of major wildpopulations of O. fragrans in China were studied using SSR and AFLP methods to discuss therelationship between population sex ratio, age structure, geographical distribution and geneticdiversity and define genetic structure. At final, it provided a reference for evolution of sexualsystem and for protection and utilization of germplasm resources in O. fragrans.1. Morphological variation of pistil in hermaphrodites and pistillode in males:Theflower structure, especially the pistil characteristic, of major cultivated sweet osmanthus at thecampus of Zhejiang A&F University and112individuals of wild sweet osmanthus in QiandaoLake, Gongcun Village and Maoweicun Village of Zhejiang province were observed. The resultsshowed pistil of hermaphrodites existed seven kinds of state to conclude three types, namelynormal pistil, degenerated pistil and aborted pistil, and the normal pistil accounted highestproportion for98%. Pistil of males was entirely degenerated, called pistillode, and existed eightkinds of state to conclude three types, namely single-layer pistillode, two-layer pistillode,three-layer pistillode; the state of two bracteal carpel accounted highest proportion for87%. Inaddition, there may be a connection between hermaphrodites and males according to pistillode.2. Flower bud differentiation in hermaphrodites and males: Flower bud differentiationregularity and rhythm between males and hermaphrodites were almost consistent and included sixmain stages. However, every stage in hermaphrodites always lagged behind that in males. At thesame time, in the same inflorescence, the apical floret in not only hermaphrodites but also males developed earlier than the lateral ones. Most significant difference between males andhermaphrodites took place at end of carpel differentiation stage. In hermaphrodites, these twocarpels gradually fused each other with developing and finally developed to a normal pistil;However, in males, with the carpels developing, there presented a cavity between two carpels,subsequently, and it became more and more conspicuous, finally two carpels developed to becomea pistillode that included two independent bracteal tissues. Males retained the developmental markof female organ. So pistillode of males could be traced to pistil of hermaphrodites. It could beinferred that males evolved from hermaphrodites and androdioecy was an transition situation fromhermaphroditism to dioecy in O. fragrans.3. The genetic diversity of wild O. fragrans: The genetic diversity and genetic structure offifteen nature populations of O. fragrans distributed in Zhejiang, Hunan, Jiangxi, Guangxi,Guangdong, Fujian were examined using fourteen SSR markers. A total of106alleles weredetected at604individuals, the number of alleles per locus ranged from6to10with an average of7.5and a mean polymorphic information content (PIC) of0.7684. At the species level, thepercentage of polymorphic bands was99.06%; the Nei’s genetic diversity (Ne) was0.3268; theShannon’s information index (I) was0.4990. At the populations level, the percentage ofpolymorphic bands in different populations ranged from64.15to100%with an average of91.89,the Nei’s genetic diversity ranged from0.2214to0.3268with an average of0.2906, the Shannon’sinformation index ranged from0.3190to0.4961with an average of0.4433. The differentiationcoefficient (Gst) among the populations was0.1139and the gene flow (Nm) was3.8886. Theresults showed there was a rich genetic diversity in O. fragrans，and a low level of geneticdifferentiation and a high level of gene flow were found among the fifteen populations, but thegenetic variation occurred mainly within each population. Genetic identity was the highest (GI=0.9861) between Zhejiang (Jd) and Hunan (Cz), indicating that the distribution of original wild O.fragrans was continuous combined the genetic differentiation and gene flow; genetic identity wascoincident among three population (Gf, Ss and Sx) of Fujian and Mental test revealed that geneticdistance was significantly related to geographical distance (r=0.2805，p=0.0240). Typicalpopulations were studied using AFLP. The results showed that (1) the degree of genetic diversityof the decline type of Jiangxi (Qn) population was obvious lower than the the stable type of Fujian(Gf) population(Qn: PPB=48.48%, Ne=0.2631, I=0.1778; Gf: PPB=79.09%, Ne=0.4148, I=0.2776), which was consistent with the results of SSR;(2)The genetic diversity of Hunan (Ly)population (the northernmost distribution of O. fragrans) was mainly same with Jiangxi (Qs)population (the southernmost distribution)(Qs: PPB=63.76%, Ne=0.2159, I=0.3244; Ly:PPB=67.57%, Ne=0.2333, I=0.3500). |
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