2018 ASHS Annual Conference

Citrus greening disease or huanglongbing (HLB) is devastating the citrus industry in Florida and elsewhere around the world. The presumed pathogen is Candidatus liberibacter asiaticus (CLas), vectored by a psyllid, Diaphorina citri. The disease weakens and eventually kills citrus trees, but in addition, affects the quality of the fruit. Oranges, symptomatic for the disease, are smaller and greener than healthy fruit and are often asymmetrical. Since the disease affects the phloem, the fruit may not be getting normal nutrients and hormones and appear slow to mature. Thus, the disease effects on quality are greater earlier in the season. HLB-symptomatic fruit generally contain less sugars, higher acidity, higher bitter limonoids and astringent flavonoids than do healthy fruit or asymptomatic HLB fruit. Studies on the juice oranges, ‘Hamlin’ and ‘Valencia’ showed that flavor degradation is worse for ‘Hamlin’ than for ‘Valencia’. Pre-harvest fruit drop is associated with this disease and fruit that are loose on HLB trees (abscission zone partially formed) have the more flavor degradation compared to fruit that are tightly held on the tree. The amount of CLas in the fruit juice correlates with sour, bitter and astringent flavor characteristics, typical of HLB-affected oranges.