Anchor peptides as innovative adjuvants reduce rain wash-off, but do not impair photosynthetic activity or cause oxidative damage in apple leaves

Rain wash-off of foliar-applied agrochemical formulations (i.e. active ingredients) is a key topic to ensure crop protection under rainy conditions and for some regions will gain higher importance due to global climate change. Rain-induced wash-off is determined by intensity and amount of rain, as well as by characteristics of the active ingredients and deposit patterns on the leaf surfaces. In addition, the micromorphology and chemical properties of the exposed surfaces equally play a significant role. Traditional approaches to reduce rain-induced wash-off focus on the use of adjuvants either to raise the penetration rate of systemic and loco-systemic formulations, or to increase adhesion of active ingredients to the target surfaces. In our studies, we evaluated the potential of novel functional proteins (anchor peptides (APs) as tool to increase rainfastness of innovative microgel formulations for slow release of active ingredient (a.i.) in pest management. For this innovative approach, we tested the adhesion capacity of the APs to bind to the leaf epicuticular surfaces of an economically important fruit crop, e.g. apple. In addition, the phytotoxic potential of APs or adjuvants on apple plants was monitored. The results indicated that the simulated rain (6.5 mm h^‑1) wash-off of the selected functional peptide Tachystatin A2-variant was just less than 2% and had no negative effects on photosynthetic activity of apple seedlings grown under -UV/+UV conditions. Coupling of novel APs in the microgel formulations might contribute to reduce the amount of agrochemicals in horticulture, and to ensure biological efficacy of plant protection treatments.