Residual toxicity of soil-applied chlorothalonil on mycorrhizal symbiosis in Leucaena leucocephala

• Published in: Plant and soil 1992-02, Vol.140 (2), p.263-268
• Main Authors: Habte, M. (Hawaii Univ., Honolulu, HI (USA). Dept. of Agronomy), Aziz, T, Yuen, J.E
• Format: Article
• Language: English
• Subjects: Acid soils; Agricultural soils; Agrochemicals products; Agronomy. Soil science and plant productions; Biological and medical sciences; CHLOROTHALONIL; CLOROTALONIL; EFECTOS RESIDUALES; EFFET RESIDUEL; Fundamental and applied biological sciences. Psychology; Fungi; Fungicides; LEUCAENA LEUCOCEPHALA; MYCORHIZE; MYCORRHIZAE; Other agrochemicals used in plant protection (herbicides, fungicides, etc.); Phytopathology. Animal pests. Plant and forest protection; Plants; Pollution effects and side effects of agrochemicals on crop plants and forest trees. Other anthropogenic factors; Pollution effects. Side effects of agrochemicals; RESIDUAL EFFECTS; Soil fungi; Soil inoculation; Soil toxicity; Soil treatment; Symbiosis
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/BF00010603

The residual effect of the fungicide chlorothalonil on the vesicular-arbuscular mycorrhizal (VAM) symbiosis was evaluated in a greenhouse experiment. The soil used was an oxisol (Tropeptic Eutrustox) treated with P to obtain target levels near-optimal for VAM activity or sufficient for nonmycorrhizal host growth. In the uninoculated soil treated with the former P level, the fungicide reduced VAM colonization of roots and completely suppressed symbiotic effectiveness measured in terms of pinnule P content. When this soil was inoculated with Glomus aggregatum, symbiotic effectiveness was significantly reduced but not eliminated by 50 mg of the fungicide kg⁻¹. At higher chlorothalonil levels, VAM effectiveness but not VAM colonization was completely suppressed in the inoculated soil. The pattern with which chlorothalonil influenced tissue P content and dry matter yield at the time of harvest closely paralleled its effect on VAM effectiveness. In the soil treated with P level sufficient for nonmycorrhizal host growth, the adverse effect of the fungicide on the above variables was appreciably milder than when the host relied on VAM fungi for its P supply. The toxic effect of the fungicide, therefore, was partly offset by P fertilization, suggesting that VAM fungi were more sensitive to chlorothalonil than the host. Our results demonstrate that although the toxic effect of chlorothalonil declined as a function of time, a significant level of toxicity persisted 12.5 weeks after the chemical was applied to soil.