Terapia fotodinâmica, nanopartículas, lignina e quitosana no tratamento de sementes de trigo para controle de Alternaria spp.

Abstract

The expansion of wheat cultivation (Triticum aestivum L.) into the Brazilian Cerrado has intensified phytosanitary challenges associated with seed-borne pathogens, particularly Alternaria alternata, which is responsible for yield losses and reductions in the physiological and sanitary quality of seeds. At the same time, conventional chemical control has shown limitations related to the selection of resistant populations, environmental impacts, and adverse effects on seed vigor, reinforcing the need for alternative, sustainable, and effective seed treatment strategies. In this context, this thesis evalu-ated the potential of emerging technologies for the control of A. alternata, including metallic and semiconductor nanoparticles (NPs) (ZnO, ZnOCl, TiO₂, and TiO₂–Fe), silver-doped (ZnO:Ag, ZnOCl:Ag) and copper-doped nanoparticles (ZnO:Cu, ZnOCl:Cu), hybrid lignate–nanoparticle for-mulations (lignate:NP), chitosan, and the combination of NPs with photodynamic therapy (PDT) us-ing methylene blue (MB) and toluidine blue. The evaluations comprised in vitro assays, treatment of naturally contaminated seeds, and analysis of seed physiological quality, considering germination, vigor, emergence, and accelerated aging. The nanoparticles ZnO, ZnOCl:10%Cu, ZnO:10%Ag, and TiO₂:5%Fe exhibited in vitro antifungal activity by inhibiting A. alternata mycelial growth, with con-trol levels ranging from 49% to 88%. In the treatment of naturally contaminated seeds, the combina-tion of ZnOCl:11%Ag associated with PDT mediated by MB achieved 93% control of Alternaria alternata, which was statistically similar to conventional chemical treatment. The lignate:ZnOCl (75:25) formulation provided 69% control, while chitosan at 4% achieved 89% control, highlighting these approaches as effective and sustainable alternatives for pathogen management in wheat seeds. None of the treatments compromised seed germination, vigor, emergence, or performance after ac-celerated aging. Overall, the results demonstrate that NPs, lignate–nanoparticle systems, chitosan, and PDT, applied individually or in combination, exhibit antifungal potential against Alternaria al-ternata and represent effective alternatives for wheat seed treatment without impairing seed physio-logical quality, contributing to the sustainability of wheat production in the Brazilian Cerrado and to the consolidation of agricultural systems aligned with food security and environmental conservation goals.