Parentage analysis of natural citrus hybrid ‘Zhelong Zhoupigan’ based on nuclear and chloroplast SSR markers

Abstract

The natural citrus germplasm ‘Zhelong Zhoupigan’ is originated in China with a history of more than 300 years. Morphology observation showed that ‘Zhelong Zhoupigan’ possessed sweet orange-like in leaf shape and fruit flesh and similar to mandarin (Citrus reticulata) in easy peeling and ruffling fruit peel, implying this variety might be a hybrid of orange and mandarin. To test this hypothesis, the genetic relationship of 20 citrus varieties were investigated by nuclear and chloroplast SSR markers (nSSR, cpSSR). Results showed that ‘Zhelong Zhoupigan’ and ‘Jincheng’ sweet orange (Citrus sinensis) were of high similarity in chloroplast pattern as they belong to a single cluster in cpSSR phylogenetic tree, and both these two varieties together with C. reticulata fell into a sub-group based on nSSR phylogenetic analysis. The similarity coefficient from the result of nSSR analysis between ‘Zhelong Zhoupigan’ and C. sinensis is 0.88 higher than that with C. reticulata (0.78). The result indicated that the chloroplast of ‘Zhelong Zhoupigan’ was derived from C. sinensis, and its nuclear genetic information derived from C. reticulata and C. sinensis with more contribution from the latter. As the chloroplast DNA is uniparentally inherited by female parent, a hypothesis was further proposed that ‘Zhelong Zhoupigan’ originated from an interspecific hybridization with C. sinensis as the female parent and C. reticulata as the male parent followed by one or more backcrosses with C. sinensis as the female parent.