Huanglongbing pathogen levels in juice across citrus genotypes do not correlate with sensory and volatile profiles

Authors: OLMEDO, GABRIELA - Orise Fellow; Jeffries, Kristen; Zhao, Wei; BALDWIN, ELIZABETH - Retired ARS Employee; LUO, WEIQI - North Carolina State University; FAN, ZHEN - University Of Florida; Sun, Xiuxiu; Mattia, Matthew; STOVER, ED - Retired ARS Employee; Plotto, Anne; Bai, Jinhe

Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Proceedings
Publication Acceptance Date: 12/1/2023
Publication Date: 12/31/2023
Citation: Olmedo, G., Jeffries, K.A., Zhao, W., Baldwin, E., Luo, W., Fan, Z., Sun, X.N., Mattia, M.R., Stover, E., Plotto, A., Bai, J. Huanglongbing pathogen levels in juice across citrus genotypes do not correlate with sensory and volatile profiles. Proceedings of Florida State Horticultural Society. 136:101. 2023.

Interpretive Summary:

Technical Abstract: Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas), has affected Florida citrus industry since 2005 causing an 80% decline in production. Despite this challenge, this industry is still one of the main economic forces for the state economy, with nearly 90% of production destined to juice processing. It is known that juice from sweet oranges (Citrus sinensis) from HLB-diseased trees is often described as less sweet and more bitter than healthy juice. Our group has previously observed a positive correlation between CLas titer and sensory quality loss in Hamlin and Valencia oranges. Here, correlation and principal component analysis (PCA) were performed between CLas titer, sensory data and volatile profiles from a large citrus genotype population including sweet orange, mandarin (C. reticulata), grapefruit (C. paradisi) and their hybrids with or without poncirus (Poncirus trifoliata) in their pedigrees. Fruit from 125 harvest/genotype combinations were used. Sample fruit were collected from mature trees grown in five different locations in Florida during five consecutive harvest seasons, from 2017/2018 to 2021/2022. After juicing, genomic DNA was extracted following a modified CTAB protocol and qPCR was performed using LJ primers targeting CLas hyv1. Results were subjected to correlation and principal component analysis (PCA) with data derived from volatile determination by HS-SPME-GC-MS and sensory descriptive evaluation with a trained panel. The analysis of CLas titer and sensory data resulted in low Pearson’s coefficients, indicating a weak or nonexistent correlation. This outcome was expected as determinations describing “species-specific” flavors, such as orange, mandarin, and grapefruit flavor, were higher for each particular species. Additionally, some negative sensory descriptors, like bitterness and aftertaste, were strongly correlated with grapefruit flavor and, as a result, often rated higher in grapefruit than in other species. In the PCA, nearly all samples with low CLas titer scored close to sweetness and orange flavor eigenvectors and away from negative sensory descriptor eigenvectors. Finally, a positive correlation was found between CLas titer and linalool content across all genotypes. Linalool is a monoterpene usually associated with fruity and sweet flavors. This is not the first time that increases in this compound are reported in HLB infected fruit versus healthy fruit. Thus, further analysis is needed to understand this observation. This study is the first to analyze how pathogen presence affects sensory attributes and volatile profile in juice from a large citrus genotype population.