The Effects of Huanglongbing and Foliar Nutritional Treatments on Orange Flavor

The citrus disease, Huanglongbing (HLB) has been demonstrated to impart off-flavor to orange fruit and juice.  This is more prevalent in fruit that are symptomatic for the disease (small, green and lopsided).  Growers in Florida are resorting to foliar nutritional spray programs for management of HLB disease, in lieu of removing symptomatic trees, to maintain tree health and yield. The impact of these programs on HLB-infected fruit flavor and aroma is unknown. This study looked at the effects of 3 different foliar nutritional spray treatments applied to healthy and HLB-infected trees for effects on flavor chemical composition and sensory quality of the fruit, and compared them with the fruit treated with a conventional spray program. Three types of fruit samples were selected: healthy fruit from non-infected trees (healthy), asymptomatic fruit from HLB-infected trees (HLBa), and symptomatic fruit from HLB infected trees (HLBs). Two varieties (Hamlin and Valencia) were investigated over multiple harvest dates and several seasons.  Differences in general between healthy and HLB fruit juice were greater for HLBs fruit, for ‘Hamlin’ variety, and earlier in the season.  Sensory differences in taste and sometimes smell between nutritionally-treated HLB fruit and healthy controls were greater in the first few years than the last years, with descriptors including more bitter, grapefruit like, sour, astringent, and metallic. The sugar/acid ratio was generally lower in HLB fruit and content of bitter limonoids higher, regardless of the nutritional treatment.  However, differences were minimal or not significant for ‘Hamlin’ in January 2012, 'Valencia' in April 2011, and 'Valencia' in April 2012, with descriptors sometimes including more sweet and more flavorful for HLB fruit juice. More seasons of study are warranted to determine if foliar nutritional treatments have any positive effect on flavor, but finding healthy trees for comparison is becoming more difficult.