2019 ASHS Annual Conference

Huanglongbing (HLB; citrus greening) is a serious endemic citrus disease caused by the bacterium Candidatus Liberibacter asiaticus (CLas). About 80-90% of citrus trees in Florida are estimated to be infected, resulting in >70% decline in citrus production over the last decade. Fruit from HLB-affected trees are often of poor quality with non-uniform peel color, lopsided, and small size. In addition, symptomatic fruit have an off flavor and higher acidity, which makes them less desirable or unmarketable. A preliminary comparative study was conducted to evaluate the effect of preharvest foliar applied mineral nutrients (K, Ca, B, and combinations) on postharvest storage life and fruit quality of HLB-affected mandarin trees. Ten-year-old, ‘LB8-9’ trees grafted on Swingle rootstock, and exhibiting mild HLB symptoms were used in this study. Eight foliar applied nutrient treatments are as follow: control (grower standard), K, Ca, B, K+Ca, K+B, Ca+B and K+Ca+B. Treatments were applied at three time points (July, September and October) in 2018. Potassium nitrate, calcium nitrate and sodium borate were used as mineral nutrient sources for K, Ca and B respectively. Randomized complete block design with four replications was used and each replicate consisted of three trees. Following harvest, fruit were stored at 25 °C with 85% relative humidity for 21 days. With K+B treatment, fruit weight, diameter, peel color ‘a’ and ‘hue’ values were increased compared with the control. Fruit compression force and peel color ‘b’ value were higher with Ca treatment than other treatments. Sensory evaluation using the general labeled magnitude scale showed higher scores for mandarin flavor intensity and sweetness, and lower scores for sourness in K- and B-treated-fruit compared with the control fruit. Overall, K and B separately and in combination improved the fruit quality attributes of HLB-affected ‘LB8-9’.