Effect of fruit abscission on orange fruit and juice quality for healthy trees and trees affected by Huanglongbing

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

Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Proceedings
Publication Acceptance Date: 7/1/2018
Publication Date: 12/30/2017
Citation: Baldwin, E.A., Plotto, A., Bai, J., Manthey, J.A., Zhao, W., Raithore, S., Irey, M. 2017. Effect of fruit abscission on orange fruit and juice quality for healthy trees and trees affected by Huanglongbing. Proceedings of Florida State Horticultural Society. 130:194-199.

Interpretive Summary: Florida citrus has been badly affected by citrus greening disease or huanglonging (HLB) with yields down over 70%. Part of the yield reduction is due to pre-harvest fruit drop, that is exacerbated by an opportunistic fungus. HLB-affected fruit have also been reported to have off-flavor compared to healthy fruit due to lower sugars, higher acids and higher bitter limonoids and astringent flavonoids. This study explored the possibility that fruit loose on the tree may have off-flavor and thus looked at shaken trees, comparing the fruit that fell off the tree when shaken to those that remained on the tree, which were then harvested for both healthy and HLB-affected trees. Study findings showed that HLB fruit were of lower flavor quality than healthy fruit generally, but that HLB fruit that dropped of the tree when shaken exhibited the lowest quality in terms of flavor chemicals and sensory analysis. There were no differences between healthy fruit that were retained or fell of the tree when shaken in quality.

Technical Abstract: Orange trees affected by huanglongbing (HLB, assumed pathogen is Candidatus liberibacter asiaticus) exhibit small and green fruit, off-flavor and excessive fruit drop. Fruit were collected from healthy and HLB-affected ‘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 lower in HLB-affected fruit, especially in HLB dropped (HLB-D) fruit juice compared to non-shaken healthy (H), healthy retained (H-R) and healthy dropped fruit (H-D). The negative impacts were more severe in early season (December) ‘Hamlins;, but less severe in the late season (January)’Hamlin’ and ‘Valencia’. 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.