Flavor of Oranges As Impacted By Abscission Zone Formation for Trees Affected By Huanglongbing Disease and Lasiodiploida Infection

Trees affected by HLB exhibit excessive fruit drop, which is exacerbated by secondary infection of the abscission zone by the fungus Lasiodiplodia. ‘Hamlin’ orange trees, both healthy and HLB symptomatic, the pathogen Candidatus Liberibacter asiaticus (CLas) later confirmed by PCR analysis, from two harvests were shaken, the dropped fruit collected, and the retained fruit harvested. Many of the dropped fruit had no calyx, while most of the retained fruit maintained their calyx after harvest. Subsequent PCR analysis of the fruit abscission zone revealed that the dropped fruit from HLB trees had higher titers of Clas and Lasiodiplodia (causal organism of postharvest stem end rot) than the retained fruit, and was the only treatment where the fruit produced ethylene. The fruit were washed, juiced, pasteurized and frozen for later chemical and sensory analyses. Sensory consumer panel difference tests showed that panelists could differentiate between dropped and retained ‘Hamlin’ fruit from HLB-affected trees, but not healthy trees, for the December harvest. This was less significant for the January harvest. A trained panel rated grapefruit, orange peel, green, oxidized oil, typical HLB flavors; sourness, umami, bitterness and metallic tastes; and tingling, astringent and burning mouthfeel highest in HLB fruit juice compared to healthy, with bitterness, metallic and bitter aftertaste being higher in dropped compared to retained HLB samples. Conversely, orange and fruity-non-citrus flavors, as well as sweet taste were lower for HLB fruit juice than for healthy and orange and sweetness lowest in HLB dropped samples. Similar results were obtained in January, although less significant. For chemical analyses, sugars and acids were lowest in dropped HLB fruit juice in December, but not in January, except for ratio. The bitter limonoids were generally higher in HLB fruit juice and highest in dropped HLB samples in December and January. This was repeated for ‘Valencia’ in April with similar results although with more differences in sugars. Overall, there were less differences for sugars and acids than for bitter limonoids, but both explained the poor flavor of HLB fruit, and especially the dropped fruit, that were loose on the tree.