2018 ASHS Annual Conference

Huanglongbing (HLB) is one of the most devastating diseases of citrus . In preliminary studies, it has been found that HLB-affected leaves often display deficiency for several nutrients. In addition, it has been reported that HLB-affected plants have compromised roots system as compared to healthy plants, which likely can reduce the water and nutrient uptake among HLB-affected plants, eventually leading in reduced productivity and decline. Several citrus growers within the state of Florida have reported to use intense and enhanced plant nutrition to compensate for the reduced root system. Commercial extracts from Ascophyllum nodosum are found to contain trace amounts of macro and micro elements, amino acids, vitamins, cytokinins, auxins, ABA-like compounds and quarternary ammonium compounds. Thus, application of Stimplex (a commercial alkaline extract of Ascophyllum nodosum) to the growing media can increase availability of mineral nutrients to the plant. Therefore, the overall goal of this study was to determine the effect of stimplex in improving nutrient uptake among healthy and HLB-affected plants.The scion and rootstock combination of ‘Valencia’ sweet orange (Citrus sinensis) and ‘Swingle citrumelo’ (C. paradisi Macf. x Poncirus trifoliata) was used in this study. Healthy (HLB-negative) and HLB-affected plants were grown on the liquid media of Hoagland solution. The plants were arranged in randomized complete block design (n=6). The four treatments included, healthy plants, HLB plants, healthy+Stimplex plants, HLB+Stimplex plants. A considerable leaf drop was observed in HLB positive plants however, HLB+Stimplex had least leaf drop during the course of experiment. HLB+Stimplex was the only treatment in which leaf chlorophyll content stayed constant throughout the experiment compared to other three treatments where the chlorophyll content decreased over time. At the end of experiment HLB+Stimplex treatment had 23% and 15% more chlorophyll compared to HLB and healthy plants, respectively. Overall, this data suggests that Stimplex application has potential to improve the performance of HLB-affected plants by improving the nutrient uptake. Nutrient analysis of the growing media, leaf nutrient analysis, assessment of reactive oxygen species, gene expression analysis for HLB and nutrient related genes is underway to understand the mechanism of HLB and Stimplex interaction. We expect that the results of this study will benefit the citrus growers in developing economical and environment friendly grove nutrient management strategies with limited use of fertilizer and enhancing nutrient availability with use of seaweed extract.