Seed treatments for the protection of crops

Abstract

This thesis focuses on the development and subsequent application of a seed treatment protocol using a phytosanitary product named T34 Biocontrol (Biocontrol Technologies S.L., Spain) containing the active ingredient Trichoderma asperellum strain T34, which is registered for use as a plant protection agent in the EU. Greenhouse and field assays were conducted in order to observe the effects of this product on Zea mays (maize) under a) abiotic stress (drought) with or without a commercial fungicide; b) biotic stress in a field naturally infected with the soil pathogen Harpophora maydis (previously known as Cephalosporium maydis). The seed treatment was also applied to seeds of two parental (male and female) lines of cucumber (Cucumis sativus) and their hybrid in order to observe its effects on yield under intensive greenhouse production. In summary, we obtained a viable seed treatment with a T34 load of up to 1·10(7) CFU/seed at baseline. T34 seed treatment was viable for up to two years with a load of 8·10(2) – 2·105 CFU/seed or up to at least 310 days with 3·10(4) – 1·10(6) CFU/seed, with or without fungicide, respectively, depending on storage and dose. In maize, regardless of water regime, T34 improved kernel P and C content, kernel dry weight and number. Under drought, T34 treatment improved leaf relative water content, water use efficiency, PSII maximum efficiency and photosynthesis. However, the seed treatment did not prevent a decline in yield in the maize genotype and stress conditions used. On the other hand, T34 reduced the percentage disease incidence by up to 13% and enhanced the final yield per plant in some maize genotypes with different levels of disease tolerance. In cucumber, T34 load in the rhizosphere was 10(6) CFU/g DW at the end of the crop cycle and it increased the early flower count and early fruit yield in male and female parental lines of cucumber in comparison to untreated plants. Moreover, in the hybrid, T34 increased total fruit yield, mean fruit weight and diameter. Finally, seeds from T34-treated plants showed a modified bacteriome, with fewer Proteobacteria and more Bacteroidetes and Firmicutes than seeds from control plants.