Non-target effects of fungicidal pea (Pisum sativum L.) seed treatment on soil microorganisms

Fungicides are widely used to control pea diseases. We investigated non-target effects of fungicide seed treatment, applied at recommended rates, on soil bacteria and fungi counts in the rhizosphere and bulk soil in Lithuania from 2008 to 2010. Microbiological analyses were conducted on the soil samples of the rhizospheric and non-rhizospheric zones of pea plants, the seeds of which either had previously been dressed with Raxil extra and Kinto or had not been dressed (control plots). Seed treatment exerted a negative effect on the fungal abundance in the pea rhizosphere. Rhizosphere fungi levels were by 40.6-33.4% lower on Raxil extra and Kinto treated pea at seedling stage compared with the untreated. At bud formation stage, the seed-treatment effect on the spread of fungi was lower. Rhizosphere bacteria amount was significantly higher than in the non-rhizosphere. In most cases, fungicide effects were positive for bacteria present both in the rhizosphere and bulk soil throughout the course of the experiment, except for seedling stage in 2010 in a wet soil. The amount of rhizosphere bacteria weakly reacted to fungicide treatment during bud formation stage in 2009, while in 2010 showed a significant positive effect. The fungicide treatment did not have any major effect on the growth of bacteria in the bulk soil during seedling stage and bud formation in both years.