Silicon and increased electrical conductivity reduce downy mildew of soilless grown lettuce |
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Authors: | Angelo Garibaldi Giovanna Gilardi Ettore Erik Cogliati Maria Lodovica Gullino |
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Institution: | (1) Centre of Competence for Agro-Environmental Innovation (AGROINNOVA), University of Torino, Via Leonardo da Vinci 44, 10095 Grugliasco, TO, Italy; |
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Abstract: | Downy mildew of lettuce, caused by Bremia lactucae, is difficult to control in soilless systems by using conventional methods of disease management because few chemicals are
registered, while resistant cultivars face the problem of resistance break down; therefore other methods for disease control
need to be investigated. The effect of silicon salt as well as increased electrical conductivities against downy mildew was
evaluated in four experiments carried out in hydroponically systems, using the cultivar of lettuce “Cobham Green”, known for
its susceptibility to the pathogen. Silicon, as potassium silicate, was added at 100 mg l−1 of nutrient solution at three levels of electrical conductivity: 1.5–1.6 mS cm−1 (EC1), 3.0–3.5 mScm−1 (EC2, 0.70 g l−1 NaCl) and 4.0–4.5 mS cm−1 (EC3, 0.95 g l−1 NaCl) respectively. Lettuce plants, grown for 14–20 (trials 1 and 2) and 36–45 (trials 3 and 4) days in the different nutrient
solutions tested, were inoculated with B. lactucae conidia with a maximum of two inoculations before final disease assessment carried out 14–21 days after the inoculation able
to give symptoms. EC and potassium silicate significantly influenced downy mildew incidence and severity, while their interaction
was not a significant factor. The addition to the standard nutrient solution (EC1) of potassium silicate resulted in a significant
reduction of downy mildew severity in trials 1 and 2 where plants were artificially inoculated 15 and 20 days after transplanting.
This efficacy was slight on plants grown for 36 and 45 days before inoculation in a soil drenched with EC1 amended with potassium
silicate. EC2 gave a significantly similar downy mildew reduction than EC2 added with potassium silicate in trial 3. Plants
grown for 36 and 45 days at the highest electrical conductivity (EC3) showed a significant reduction in severity of downy
mildew compared with that observed at EC2 level. The best results, in terms of disease control, were given by the addition
of potassium silicate to the EC3 solution. This combination also led to a significantly increased plant biomass. The possibility
and benefits of applying potassium silicate and increased EC amendments in practice is discussed. |
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