2018 ASHS Annual Conference

Huanglongbing (HLB aka citrus greening) is a serious endemic citrus disease presumed to be caused by Candidatus Liberibacter asiaticus (CLas) and is vectored by the Asian citrus psyllid. About 80 to 90% of citrus trees in Florida are estimated to be infected by CLas; resulting in >70% decline in citrus production over the last decade. HLB-affected plants showed blotchy mottling on leaves, twigs dieback, reduced fibrous root density, and stunted growth which leads to the shorter lifespan. Preliminary studies show that enhanced mineral nutrition helps in maintaining growth and productivity of CLas-infected plants. Mineral nutrition seems to overcome stress in HLB-affected plants; however, soil pH directly impacts on specific nutrients availability and uptake pattern. Therefore, a comparative greenhouse study was conducted to evaluate the nutrient uptake with different pH ranges in healthy and HLB-affected plants. This study was designed as a completely randomized block design with four replicates of each healthy and CLas-infected plants grown in hydroponic culture (with Hoagland solution). The pH range i.e. 6-6.5, 6.5-7, 7-7.5, 7.5-8 and 8-8.5 were maintained in Hoagland solution by adding acid/base on alternate days for five-week growing period. Under pH 6-6.5 range, CLas-infected plants showed increased chlorophyll content (%), leaf number and shoot growth (% increase), leaf nitrogen and zinc content; and, decreased calcium and manganese leaf contents compared to higher pH ranges. Hoagland nutrient analysis showed increase in nitrogen, potassium, calcium, magnesium, and boron uptake at pH 7-7.5 range in healthy and HLB-affected plants. Overall, HLB-affected plants showed better growth at pH 6-6.5 than healthy plants. In addition, the interaction of HLB and reactive oxygen species (ROS) and genes expression analysis related to nutrients will be determined. With this study, we expect to develop better understanding of HLB, pH of growing media, and nutrient absorption interaction with changing pH; these results will help in selection of favorable pH range for fertigated citrus to maintain optimal plant growth under HLB prevailing conditions for commercial groves.