Variable Manganese Rates Influence the Performance of Huanglongbing-affected Citrus Trees in Florida

Abstract

Improving nutrient uptake and tree health play an important role in managing Huanglongbing (HLB)-affected citrus trees in Florida. A greenhouse experiment was conducted to evaluate the effect of increasing rates of manganese (Mn) on growth and development of sweet orange [Citrus sinensis (L.) Osbeck] trees at the University of Florida’s Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center in Lake Alfred, FL. Half the trees were graft-inoculated with the HLB pathogen and the remainder were used as the HLB-free (non HLB) control trees. Four rates of Mn (0.0 kg·ha21 Mn (Control), 5.6 kg·ha21 Mn (1x—standard rate), 11.2 kg·ha21 Mn (2x—standard rate), and 22.4 kg·ha21 Mn (4x—standard rate) were split applied quarterly to both sets of the trees in a completely randomized design. There were seven single tree replicates for each treatment. Response variables measured were trunk diameter, tree height, leaf Mn concentration, plus above- and belowground biomass. The accumulated Mn in leaf tissues significantly increased trunk diameter but did not affect tree height for both HLB-affected and non-HLB trees, the 2x rate had the maximum value for trunk diameter relative to the 4x rate. This study established a positive correlation between soil available Mn with Fe and Cu, but negative correlation with B and Zn. A strong correlation of 20.76, 20.69, and 0.65 was observed between soil Mn and B, Zn, and Cu, respectively, as compared with 0.49 with Mn and Fe. Among HLB-affected trees, the 2x rate gave the most belowground dry matter, which was 3% greater than the control and 5% greater than 4x. Aboveground dry matter had at least 30% more biomass than belowground matter among all treatments within HLB-affected trees. For small and medium roots, Mn accumulation increased with Mn application until 2x rate and decreased thereafter for HLB-affected trees. The results from our study showed an Mn rate of 8.9–11.5 kg·ha21 Mn, as the optimum Mn level for young ‘Valencia’ HLB-affected trees in Florida.