New insights in the flavor and chemistry of Huanglongbing tolerant citrus hybrids with/without Poncirus trifoliata in their pedigree

Authors: Jeffries, Kristen; FAN, ZHEN - University Of Florida; Sun, Xiuxiu; OLMEDO, GABRIELA - Orise Fellow; Zhao, Wei; Mattia, Matthew; STOVER, ED - Retired ARS Employee; BALDWIN, ELIZABETH - Retired ARS Employee; MANTHEY, JOHN - Retired ARS Employee; Breksa, Andrew; Bai, Jinhe; Plotto, Anne

Submitted to: Frontiers in Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2024
Publication Date: 9/10/2024
Citation: Jeffries, K.A., Fan, Z., Sun, X.N., Olmedo, G., Zhao, W., Mattia, M.R., Stover, E., Baldwin, E., Manthey, J., Breksa Iii, A.P., Bai, J., Plotto, A. New insights in the flavor and chemistry of Huanglongbing tolerant citrus hybrids with/without Poncirus trifoliata in their pedigree. Frontiers in Horticulture. 3:1425366. 2024. https://doi.org/10.3389/fhort.2024.1425366.
DOI: https://doi.org/10.3389/fhort.2024.1425366

Interpretive Summary: Some Citrus hybrids, including mandarins, and citrus hybrids introgressed with Poncirus trifoliata, a relative of Citrus, have shown tolerance to the citrus greening disease Huanglongbing (HLB), which has decimated orange and grapefruit commercial production. These hybrids have a wide range of flavor characteristics and need to be classified into orange or mandarin for juice production. This classification is based on either sensory qualities, chemical composition or both. This study evaluated thirteen genotypes including commercial orange and mandarins as well as hybrids with Poncirus in their background. Sensory qualities ranged from acceptable orange or mandarin flavor to highly sour, bitter with grapefruit, pumpkin or “poncirus-like” off-flavor. Esters, some sesquiterpenes, along with the flavonoids, eriocitrin and quercetin 3-(3R-glucosylrutinoside), were positively correlated with orange flavor while ß-ionone and eucalyptol were highly abundant in the mandarin hybrids. Poncirus hybrids had higher abundance of the flavonoids hesperetin-7-galactoside and linarin, and the coumarins, osthole, meranzin, and isomeranzin. Two mandarin hybrids, FF-5-6-36 and FTP-6-32-67, were not bitter at harvest, but exhibited delayed bitterness when tasted after several months in storage at -20 °C. Some flavonoids and limonoids increased significantly in stored juice, likely contributing to bitterness in those samples. Identifying compounds responsible for off flavor and bitterness in citrus is key to making sure some genotypes are not selected for further evaluation in a breeding program.

Technical Abstract: Citrus hybrids with Poncirus trifoliata L. Raf. introgression have gained interest due to their tolerance to Huanglongbing (HLB), a devastating disease for Florida citrus agriculture. While these hybrids inherit disease tolerance from P. trifoliata, they sometimes also suffer from undesirable off-flavors. A selection of thirteen genotypes were harvested over the 2020-2021 and 2021-2022 seasons. Their juices were evaluated by a trained sensory panel and were comprehensively analyzed for their chemical makeup, including soluble solids content (SSC), titratable acidity (TA), volatiles, flavonoids and limonoids. Overall, along with the commercial orange cultivars ‘Valencia’ and ‘Hamlin’, the HLB-tolerant Poncirus hybrid ‘US SunDragon,’ and the mandarin hybrids Sugar Belle®, FF-5-51-2, and ‘US Superna’ had positive citrus flavor quality. Esters, some sesquiterpenes, along with flavonoids, eriocitrin and quercetin-3-(3R-glucosylrutinoside), were positively correlated with orange flavor while ß-ionone and eucalyptol were highly abundant in the mandarins. The flavonoid linarin, was more abundant in Poncirus hybrids with off-flavors than in the Poncirus hybrid ‘US SunDragon’, having high orange flavor. Two mandarin hybrids, FF-5-6-36 and FTP-6-32-67, were not bitter at harvest, but the juice exhibited delayed bitterness after storage at -20 °C, which was associated with significant increases of limonin, nomilin, naringenin, and prunin. Interestingly, during freezer storage, a newly identified flavonoid in citrus, tricin-C-hexoside, increased dramatically across all of the genotypes. The identification of disease-tolerant hybrids with satisfactory flavor quality at juicing as well as after storage where delayed bitterness may develop, has great significance for future breeding efforts for fresh fruit or for use in stand-alone juice/juice blends.