Effect of abscission zone formation on orange (Citrus sinensis) fruit/juice quality for trees affected by Huanglongbing (HLB)

Authors: Baldwin, Elizabeth - Liz; Plotto, Anne; Bai, Jinhe; Manthey, John; Zhao, Wei; RAITHORE, SMITA - Symrise Ag; IREY, MIKE - Southern Gardens Citrus

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2018
Publication Date: 2/7/2018
Citation: Baldwin, E.A., Plotto, A., Bai, J., Manthey, J.A., Zhao, W., Raithore, S., Irey, M. 2018. Effect of abscission zone formation on orange (Citrus sinensis) fruit/juice quality for trees affected by Huanglongbing (HLB). Journal of Agricultural and Food Chemistry. doi:10.1021/acs.jafc.7b05635.
DOI: https://doi.org/10.1021/acs.jafc.7b05635

Interpretive Summary: Citrus greening disease or huanglongbing (HLB) is devastating the citrus industry around the world, but especially in Florida where yields are down by 70%. The disease causes pre-harvest fruit drop and reduces flavor quality of the fruit and juice. This study shows that fruit that are loose on the tree, which may still be harvested, exhibit inferior flavor compared to fruit that are held tightly to the tree by both chemical and sensorial analyses. These fruit also show higher levels of the bacterial pathogen responsible for the disease but also of a fungal pathogen that has been shown in previous studies to loosen the fruit on the tree. This information gives the industry options to reduce the fungal pathogen through use of fungal sprays, or to use other treatments that prevent fruit loosening on the tree, thus reducing fruit drop and enhancing flavor quality.

Technical Abstract: Orange trees affected by huanglongbing (HLB) exhibit excessive fruit drop, and fruit loosely attached to the tree may have inferior flavor. Fruit were collected from healthy and HLB-infected (Candidatus liberibacter asiaticus) ‘Hamlin’ and ‘Valencia’ trees. Prior to harvest, the trees were shaken, fruit that dropped collected, tree-retained fruit harvested and all fruit juiced. For chemical analyses, sugars and acids were generally lowest in HLB dropped (HLB-D) fruit juice compared to non-shaken healthy (H), healthy retained (H-R) and healthy dropped fruit (H-D) in early season (December) but not for the late season (January)’Hamlin’ or ‘Valencia’ except for sugar/acid ratio. The bitter limonoids, many flavonoids and terpenoid volatiles were generally higher in HLB juice, especially HLB-D juice, compared to the other samples. The lower sugars, higher bitter limonoids, flavonoids and terpenoid volatiles in HLB-D fruit, loosely attached to the tree, contributed to off-flavor as was confirmed by sensory analyses.