Sensory and Chemical Characteristics of Citrus x Poncirus Hybrids

Hybrids of Citrus x Poncirus trifoliata are currently receiving great interest as a possible source of genetic material for citrus breeding as they appear to be less susceptible to Huanglongbing, a deadly citrus disease caused by Candidatus Liberibacter. However, Citrus x Poncirus hybrids typically produce fruit with unacceptable flavor.  To develop Citrus x Poncirus hybrids that are commercially acceptable, it is essential to develop an understanding of Poncirus impact on citrus flavor.  Quality characteristics of six Citrus x P. trifoliata hybrids were compared with C. reticulata hybrids early (Oct-Nov) and late (Jan-Feb) in the 2012-13 season.  Fruit were evaluated for overall quality by sensory and chemical analyses. Samples showed a wide range of palatability and composition, regardless of pedigree. US 119 and 6-23-20 had the most similar flavor to P. trifoliata due to high bitterness and aftertaste. Volatile composition of 6-23-20 was the closest to P. trifoliata, with high amount of esters, monoterpenes and sesquiterpene hydrocarbons, followed by US 119.  All P. trifoliata hybrids produced more aldehydes than fruit with no P. trifoliata in their pedigree, except for 6-23-20. Fruit of 5-18-24, 1-77-105 and ‘Fortune’ were characterized by high sourness. Fruit of 1-76-100 and 5-18-31 had the highest sweetness, floral and fruity-non-citrus flavor, and fruit of 5-18-31 had the highest tangerine flavor, indicating a potential for high quality. Sweetness and sourness were explained by sugars and acids, although some volatiles (carvone and linalool) appeared to contribute to sweetness. Bitterness was not explained by the bitter limonoids, which were the highest in the sweetest fruit (1-76-100), but it could be explained by a combination of low sugars and high monoterpene and sesquiterpene hydrocarbons. In addition to highlighting chemical contributors to sensory descriptors in Citrus x P. trifoliata hybrids, this study provides useful information on sensory quality for future citrus breeding efforts.