Abstract
Florida orange trees have been affected by huanglongbing (HLB) for more than a decade. To alleviate disease-caused tree decline, maintain fruit productivity, and reduce disease transmission, enhanced foliar spray programs combining vector control and nutritional supplementation have been applied to healthy and diseased trees. The aim of this research was to discover if the various foliar sprays affect fruit peel oil chemical components. In this study, “Valencia” orange trees, with or without HLB (HLB±), were treated with the grower standard program (control, C) or one of four proprietary enhanced foliar spray programs (N1, N2, N3, and N4) over 16 months. Compared with HLB−, HLB+ samples had lower concentrations of typical peel oil components, including valencene, octanal, and decanal, and were abundant in oxidative/dehydrogenated terpenes, such as carvone and limonene oxide. However, limonene, the dominant component, was not affected by any treatment. Control and three out of four enhanced foliar spray programs, N2, N3, and N4, had very little influence on the chemical profiles of both HLB− and HLB+ samples, while N1 treatment greatly altered the chemical profile of HLB+ samples, resulting in peel oil similar to that of HLB− samples.
Highlights
Huanglongbing (HLB, or citrus greening), associated with the bacterium Candidatus Liberibacter asiaticus (CLas), is a very destructive citrus disease and is vector-transmitted by the Asian citrus psyllid (ACP; Diaphorina citri Kuwayama)
Standards were obtained from the following sources: octanal, nonanal, decanal, terpinyl aldehyde, (E,E)-2,4-decadienal, geranial, neral, octanol, linalool, citronellol, nerol, α-pinene, myrcene, and β-phellandrene were purchased from Aldrich (Milwaukee, WI, United States); valencene was bought from Bedoukian (Danbury, CT, United States); undecanal from Analabs (North Haven, CT, United States); sabinene was obtained from Treatt (Lakeland, FL, United States); δ-3-carene was from K&K (Royse City, TX, United States); terpinen-4-ol from Advanced Biotech (Totowa, NJ, United States); and α-humulene from Fluka (Buchs, Switzerland)
Because the CLas titer in orange juice is much lower than in leaf tissue, we used another pair of primers targeting at CLas hyv1, which has more copies in the genome than that of rDNA (Morgan et al, 2012)
Summary
Huanglongbing (HLB, or citrus greening), associated with the bacterium Candidatus Liberibacter asiaticus (CLas), is a very destructive citrus disease and is vector-transmitted by the Asian citrus psyllid (ACP; Diaphorina citri Kuwayama). Trees rapidly decline and eventually die (Bové, 2006; Gottwald et al, 2020). HLB-infected trees still produce fruits, with decreased yield and poor quality. Fruits and juice from HLB-diseased trees are associated with low soluble sugar and ethyl butanoate, as well as high acid, limonoid, and flavonoid content, resulting in less sweet and fruity flavor with more sour and bitter taste (Dala-Paula et al, 2018).
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