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Introduction: 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. Methods: 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. Results & discussion: 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 b-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 diseasetolerant 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. [ABSTRACT FROM AUTHOR]

Sweet orange (Citrus sinensis) exhibits limited genetic diversity and high susceptibility to Huanglongbing (HLB). Breeding HLB-tolerant orange-like hybrids is in dire need. However, our understanding of the key compounds responsible for orange flavor and their genetic regulation remains elusive. Evaluating 179 juice samples, including oranges, mandarins, Poncirus trifoliata, and hybrids, distinct volatile compositions were found. A random forest model predicted untrained samples with 78% accuracy and identified 26 compounds crucial for orange flavor. Notably, seven esters differentiated orange from mandarin flavor. Cluster analysis showed six esters with shared genetic control. Differential gene expression analysis identified C. sinensis alcohol acyltransferase 1 (CsAAT1) responsible for ester production in orange. Its activity was validated through overexpression assays. Phylogeny revealed the functional allele was inherited from pummelo. A SNP-based DNA marker in the coding region accurately predicted phenotypes. This study enhances our understanding of orange flavor compounds and their biosynthetic pathways and expands breeding options for orange-like cultivars.k [ABSTRACT FROM AUTHOR]