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Nowadays, Huanglongbing (HLB) disease, commonly known as “yellow dragon disease”, affects citrus crops worldwide and has a devastating effect in the agro-industrial sector. Significant efforts have been made to fight the illness, but still, there is no effective treatment to eradicate the disease. This work is the first approach to evaluate the capacity of silver nanoparticles (AgNPs) to directly eradicate the bacteria responsible for Huanglongbing disease, Candidatus Liberibacter asiaticus (CLas), in the field. The AgNPs were administered by foliar sprinkling and trunk injection of 93 sick trees with remarkable results. Both methods produce an 80–90% decrease of bacterial titre, quantified by qRT-PCR in collected foliar tissue, compared with the control group. Scanning electron microscopy images show an essential reduction of starch accumulation in phloem vessels after AgNP treatments without evidence of bacteria in the analyzed samples. Compared with other effective methods that involve β-lactam antibiotics, the potency of AgNPs is 3 to 60-times higher when it is administered by foliar sprinkling and from 75 to 750-fold higher when the administration was by trunk-injection. All these results allow us to propose this AgNP formulation as a promising alternative for the treatment of infected trees in the field.

Betulin (90–94%) was extracted from birch with a non-polar solvent and recrystallized from 2-propanol. Liquid-phase oxidation of betulin aimed at obtaining its biologically active oxo-derivatives (betulone, betulonic and betulinic aldehydes), exhibiting e.g. antitumor, anti-inflammatory, antiparasitic, anticancer and anti-HIV properties, was demonstrated for the first time over gold-based catalysts. Gold was deposited on pristine TiO2 and the same support modified with ceria and lanthana, followed by pretreatment with a H2 or O2 atmosphere. The catalysts were characterized by XRD, BET, ICP, TEM, XPS, DRIFT CO, TPD of NH3 and CO2 methods. The nature of the support, type of modification and the pretreatment atmosphere through the metal–support interactions significantly influenced the average particle size of gold, its distribution and the electronic state of gold, as well as the acid–base properties and, thereby, the catalytic performance (activity and selectivity) in betulin oxidation. Au/La2O3/TiO2 pretreated in H2 displayed the highest catalytic activity in betulin oxidation among the studied catalysts with selectivities to betulone, betulonic and betulinic aldehydes of 42, 32 and 27%, respectively, at 69% conversion. Side reactions resulting in oligomerization/polymerization products occurred on the catalyst surface with the participation of strong acid sites, diminishing the yield of the desired compounds. The latter was improved by adding hydrotalcite with the basic properties to the reaction mixture containing the catalyst. Kinetic modelling through numerical data fitting was performed to quantify the impact of such side reactions and determine the values of rate constants.