2018 ASHS Annual Conference

Huanglongbing (HLB)-affected oranges are typically green or yellow in color, rather than orange, and the latter is more common in the Florida citrus groves. The yellow color is often associated with insufficient accumulation of carotenoids (the reason for lack of orange color) in the flavedo, lack of natural shine, and shriveled peel (due to water loss). The green color is an indicator of maturity due to HLB-associated phloem malfunction and resulting retarded growth and development of the fruit. All HLB-affected fruit produced a lower volume of peel oil compared to healthy fruit, however, only green fruit showed substantially different volatile profiles from healthy fruit. The green fruit contained low concentrations of most of sesquiterpene hydrocarbons and derivatives, such as, nootkatone, valencene, α-selinene, 7-epi-α-selinene and caryophyllene oxide, some monoterpene hydrocarbons and derivatives with orange/citrus characteristics, such as, limonene, myrcene, α-pinene, neral, geranial, and α-terpineol, and straight-chain aldehydes, such as, octanal, nonanal and decanal. However, eight compounds were determined in the green fruit peel which were not present, or present in very minor quantities, in the healthy fruit. Other compounds found more in HLB-affected green fruit than in healthy fruit feel oils were cis-3-hexenol, cis-pinocarveol, carvone, and α-cubebene.