Molecular evidence for the natural hybrid origin of Phalaenopsis × intermedia Lindl

In order to confirm the hybrid origin of Phalaenopsis × intermedia Lindl., internal transcribed spacers (ITSs) of ribosomal DNA (rDNA) and three fragments of chloroplast DNA (cpDNA) were studied. Nineteen clones of ITS sequences from three accessions of P. × intermedia Lindl. were aligned with nine species of sections of Phalaenopsis and Stauroglottis that were candidate parents.A phylogenetic tree, derived from the ITS data, was constructed by the Neighbor-joining (NJ) method.Two major groups were shown for 19 clones of ITS sequences of P. × intermedia based on the phylogenetic tree. The average genetic distance between the aforementioned two groups and the candidate parents was calculated based on the Kimura 2-parameter method. One group had the lowest genetic distance from the ITS repeat sequences of P. aphrodite Rchb.f., and another group had the lowest distance from that of P. equestris (Schauer) Rchb.f.The results indicated that both P. aphrodite and P. equestris are parents of P. × intermedia based on the ITS data. In addition, analysis of three fragments of cpDNA, namely the trnL intron, the trnL-trnF intergenic spacer (IGS), and the atpB-rbcL IGS, showed that P. × intermedia had the lowest genetic distance from P. aphrodite. Both the ITS and cpDNA data, as well as reference to the effects of maternal inheritance of cpDNA, suggest that P. aphrodite was the maternal parent and P. equestris was the paternal parent of P. × intermedia.Therefore, molecular evidence supports P. × intermedia being a natural hybrid derived from P. aphrodite and P. equestris