PT - JOURNAL ARTICLE AU - Schmitz, Christine AU - Luedeling, Eike AU - Pariyar, Shyam TI - Synergism and phytotoxicity: the effects of tank-mix additives on the biological efficacy of Cu<sup>2+</sup> against <em>Venturia inaequalis</em> and <em>Podosphaera leucotricha</em> AID - 10.1101/2022.11.08.515630 DP - 2022 Jan 01 TA - bioRxiv PG - 2022.11.08.515630 4099 - http://biorxiv.org/content/early/2022/11/09/2022.11.08.515630.short 4100 - http://biorxiv.org/content/early/2022/11/09/2022.11.08.515630.full AB - The wetting behaviour of the spray and biological efficacy of Cu2+ active ingredients in agrochemical formulations may be enhanced by tank-mix additives. We investigated how three BREAK-THRU® additives (BT301: biodegradable, BT133 and BT420: bio-based and biodegradable) as tank-mix with commercial copper preparations influence the spray distribution, leaf uptake and biological efficacy of copper additive mixtures against apple scab and apple powdery mildew under controlled conditions. We quantified the synergetic effects of these additives in foliar applications. In addition, we determined the phytotoxic potential and evaluated impacts on photosynthetic activity, non-photochemical quenching and ROS activity. The additives BT301 and BT420 strongly reduced surface tension and contact angle of copper treatments. The fluorescence observations revealed that BT301 achieved better spreading of copper formulation with more complete coverage of the leaf surface than BT420 and BT133, whereas “coffee-ring” spreading was observed with BT133. The additive BT301 showed an increase in relative fluorescence area, indicating higher ROS production as a signal of intra-cellular tissue activity. The photochemical efficiency of photosystem II (Fv/Fm) was not negatively influenced by copper or additive treatment. Thus, we observed no phytotoxic effects of copper-additive mixtures on apple leaves at treatment doses of 4 g Cu2+ L-1. All copper treatments reduced apple scab infestations significantly, by 53-76%. Interestingly, addition of BT301 to copper preparations showed the strongest biological efficacy (83% reduction) against V. inaequalis, whereas addition of BT420 showed the strongest effect against P. leucotricha (89% infection reduction). The synergetic effects of additives on the biological efficacy without phytotoxic effects on plants may have potential for reducing copper loads in horticultural production systems.Competing Interest StatementThe authors have declared no competing interest.BT133BREAK-THRU® SP 133BT133CupCuprozin® progress with BREAK-THRU® SP 133BT133FungFunguran® progress with BREAK-THRU® SP 133BT301BREAK-THRU® S 301BT301CupCuprozin® progress with BREAK-THRU® S 301BT301FungFunguran® progress with BREAK-THRU® S 301BT420BREAK-THRU® SF 420BT420CupCuprozin® progress with BREAK-THRU® SF 420BT420FungFunguran® progress with BREAK-THRU® SF 420CFIChlorophyll fluorescence imagingCupCuprozin® progressETRElectron transport rate (μmol m-2 s-1)Fm’Maximum fluorescence yieldFungFunguran® progressFv/FmPhotochemical efficiency of photosystem IIH2DCFDA2’,7’-dichlorofluorescin diacetateNOQuantum yield of nonregulated energy dispassionNPQQuantum yield of regulated energy dispassionPARPhotoactive radiation (μmol m-2 s-1)PS(II)Effective quantum yield of photosystem IITEGO_CuTEGO® XP 11052