| Abstract: | The leaf or bark tissue extracts of 108 biotypes of Citrus and its five related genera were analyzed by polyacrylamide gel electrophoresis for isozymes ofperoxidase, glutamate oxaloacetate transaminase, phosphoglucose isomerase,phosphoglucose mutase, superoxide dismutase, tetrazolium oxidase,NADP+- dependent malate dehydrogenase and esterase. The inter-or intra-genericdifferences of isozymograms were compared. Dissimilarities of the isozyme patternsamong the samples were calculated by computer based on the UPGMA methodto demonstrate the phylogenetic relationship of the biotypes. There are remarkableisozymogramatic differences among the six genera. Generally speaking, each genuspossesses its own unique bands. Based on the cluster analysis, the total Citrusbiotypes are classified into seven groups, i.e. Honghe papeda, Mauritius papeda,Pummelo, Ichang papeda, Citron, Lemon-lime and Mandarin-orange. Ichang papeda is suggested to be the third subgenus of the genus Citrus. The Fuming trifoliata orange is accepted as a new species of Poncirus-P. polyandra S. Q. Ding. It might be the evolutionary bridge between Poncirus and Citrus, and one of the “missing links” as suggested by W. T. Swingle. Microacrumen (small- fruited mandarin) is the primitive form of the mandarins. It seems better to consid er“ Horse-nose mandarin ”or “Xipigoushigan mandarin” as the typic mandarinoriginated in China. Euacrumen (large-fruited mandarin) might have arisedthrough two ways. One is hybridization of Microacrumen and C. sinensis, andthe other is just the variation of Microacrumen. Ancestors of some biotypes areinferred based on isozyme data. Fortunella obovata Tan. may be a hybrid ofFortunella and Citrus. C. unshiu Marc. arose from the nucellar mutationof“Huangyanbendiguangju mandarin”( C. nobilis Lour.) in Huangyan ofZhejiang Province. C. junos Sieb. came from hybridization of Ichang papeda andmandarin. C. grandis Osbeck and mandarin may have been involved in the originof C. aurantium L.. C. limonia Osbeck may be a hybrid between C. medica L.and mandarin. The evolutionary trend of citrus fruit trees is proposed, anda tentative phylogenetic diagram is drawn. |
