Chemical Variability of Peel and Leaf Essential Oils in the Citrus Subgenus Papeda (Swingle) and Few Relatives

The Papeda Citrus subgenus includes several species belonging to two genetically distinct groups, containing mostly little-exploited wild forms of citrus. However, little is known about the potentially large and novel aromatic diversity contained in these wild citruses. In this study, we characterized and compared the essential oils obtained from peels and leaves from representatives of both Papeda groups, and three related hybrids. Using a combination of GC, GC-MS, and C-13-NMR spectrometry, we identified a total of 60 compounds in peel oils (PO), and 76 compounds in leaf oils (LO). Limonene was the major component in almost all citrus PO, except for C. micrantha and C. hystrix, where beta-pinene dominated (around 35%). LO composition was more variable, with different major compounds among almost all samples, except for two citrus pairs: C. micrantha/C. hystrix and two accessions of C. ichangensis. In hybrid relatives, the profiles were largely consistent with their Citrus/Papeda parental lineage. This high chemical diversity, not only among the sections of the subgenus Papeda, but also between species and even at the intraspecific level, suggests that Papeda may be an important source of aroma diversity for future experimental crosses with field crop species.