Abstract: The glutamate oxaloacetate transaminase isozymes (GOT) extracted from 125 biotypes of Citrus and its relatives, Fortunella, Poncirus and Microcitrus were analyzed using polyacrylamide gel electrophoresis to investigate the taxonomic relationships among citrus plants. Besides all the isozymes reported before, two new bands were detected and designated their putative alleles B and C in GOT-l. Among pummelo cultivars wide variations were found. Most of the mandarins were identical, having SS for GOI-1 and MM for GOT-2 except for Zou-Pi-Gan and Yao-Gan, which both had FS at GOT-1 and might be hybrids. This finding suggests that all of the mandarins may have originated from a common ancestor. Sour orange biotypes showed a considerable variation in GOT isozymes. Most of the sour oranges in China were assumed to be hybrids between pummelo and mandarin based on GOT isozyme patterns, but two biotypes, Xiao-Hong-Cheng and Zhu-lan, had FS at GOT-1 and MB at GOT-2, which strongly suggests that they be hybrids of pummelo and Ichang papeda because B allele of GOT-2 occurs only in Ichang papeda and its close relatives Yuzu and Ichang lemon. From this study Yuzu is assumed to be derived from hybridizationof Ichan, papeda and mandarin.

Key words: Citrus, Poncirus, Fortunella, Microcitrus, GOT isozymes