Functionalized dextrin-based nanosponges as effective carriers for the herbicide ailanthone

Ailanthone, a quassinoid from Ailanthus altissima (Mill.) Swingle, is a natural herbicide, whose use is limited by its low persistence and rapid degradation in organic substrates. Dextrin-based nanosponges (NSs) are polymers with a cage-like structure that can complex several molecules, acting as carriers or protectors. Their encapsulation efficiency can be exploited in numerous applications. Hence this study explored at first the biological activity of eight different dextrin-based NSs, synthesized with 1,1′ -carbonyldiimidazole (CDI) or pyromellitic dianhydride (PYRO) (αNS-CDI, βNS-CDI, γNS-CDI, LC NS-CDI, αNS-PYRO, βNS-PYRO, γNS-PYRO, and LC NSPYRO), towards two model species (Lepidium sativum L. and Raphanus sativus L.) in filter paper under controlled conditions in laboratory. Then, the selected dextrin-based NSs were loaded with ailanthone and applied in the concentration of 7.5 or 30 mg L 1 of ailanthone in pre-emergence on the same species, initially on filter paper and subsequently on cultivation substrate for horticulture. In all three bioassays, the number of germinated seeds and the length of developed roots and hypocotyls were evaluated. In the first bioassay, the results showed that five dextrin-based NSs promoted the germination and root elongation, thus counteracting the herbicidal effect of ailanthone. Hence, three selected formulations (αNS-CDI, γNS-CDI, and LC NS-CDI) were loaded with ailanthone, with γNS-CDI providing the highest loading capacity (1.36%) and encapsulation efficiency (55.15%). In the second bioassay, the phytotoxic activity of ailanthone was strengthen by dextrin-based NSs, always stronger by at least 58% than the pure compound across 30 days in paper, without differences between formulations. In the third bioassay, loading ailanthone in γNS-CDI also prolonged its herbicidal activity, still reducing to only 20% the germination and growth of garden cress and radish 30 and 20 days after treatment, respectively. Overall, results demonstrated that dextrin-based nanosponges can be proposed as suitable carriers in the formulation of ailanthone-based herbicide. Their use both increased and extended the phytotoxic activity of ailanthone, leading to the possibility of reducing the amount applied for each treatment, or reducing the number of herbicide treatments.