THE EFFECT OF FUNGICIDES ON VESICULAR-ARBUSCULAR MYCORRHIZAL SYMBIOSIS .1. THE EFFECTS ON VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI AND PLANT-GROWTH

This paper describes the effects of the fungicides Benlate, Aliette an d Ridomil on plant growth and on mycorrhizal development in onion plan ts. An attempt was made to distinguish effects on plants from those on the fungus by making comparisons between mycorrhizal plants in the ab sence of added phosphorus and non-mycorrhizal equivalent size plants. Vital staining techniques were used to analyse the effects of the fung icides on the living fungus both within the root and in the soil. Benl ate had no effect on shoot dry weight or root length of onion plants w hereas a reduction in plant growth was observed following the applicat ion of Aliette or Ridomil, in comparison to control plants. Benlate ha d negative effects on the numbers of living internal hyphae, arbuscule s, fungal-plant interface and living external hyphae in the soil. Alie tte had no effect on the number of living intercellular hyphae and arb uscules. However, it markedly reduced the root length and the length o f infected root per plant. These combined effects led to a reduction i n the area of the interface between fungus and plant. The length of ex ternal hyphae per gram of soil was reduced following the application o f Aliette, though not as severely as with Benlate. Ridomil had more co mplex effects on vesicular-arbuscular mycorrhizal symbiosis; treated p lants showed a reduction in plant growth and also a reduction in all f ungal parameters, namely the number of living intercellular hyphae, ar buscules and fungal-plant interface, the length of infected root and t he development of external hyphae in the soil.