The effect of fungicides on vesicular–arbuscular mycorrhizal symbiosis

Abstract

This paper describes the effects of the fungicides Benlate, Aliette and Ridomil on plant growth and on mycorrhizal development in onion plants. An attempt was made to distinguish effects on plants from those on the fungus by making comparisons between mycorrhizal plants in the absence of added phosphorus and non-mycorrhizal equivalent size plants. Vital staining techniques were used to analyse the effects of the fungicides on the living fungus hoth within the root and in the soil.Benlate had no effect on slioot dry weight or root length of onion plants wliereas a reduction in plant growth was observed following the application of Aliettc or Ridomil, in comparison to control plants. Benlate had negative effects on the numbers of living internal hyphae, arbuscules, fungal-plant interface and living external hyphae in the soil.Aliette had no effect on the number of li\ ing intercellular hyphae and arbuscules. Howe\ er, it markedly reduced the root length and the length of infected root per plant. These combined effects led to a reducti(Mi in the area of the interface between fungus and plant. The length of external hyphae per gram of soil was reduced following the application of Aliette, though not as severely as with Benlate.Ridomil had more complex effects on vesicular-arbuscular mycorrhizal symbiosis; treated plants showed a reduction in plant growth and also a reduction in all fungal parameters, namely the number of living intercellular hyphae, arbuscules and fungal-plant interface, the length of infected root and the development of external hyphae in the soil.

Field evidence for the carbon cost of citrus mycorrhizas

“…There are several possible reasons to explain why trees did develop P deficiency : (1) trees were planted from the commercial nursery with stored P ( 0n20 % leaf P) that was re-allocated for growth ; (2) root systems had pre-established mycorrhizal colonization when transplanted, and even though further development and activity was inhibited by benomyl, some mycorrhizal-mediated uptake of P occurred even at low P supply ; (3) slow-growing perennial Citrus on the four rootstocks had a relatively low P demand compared with supply of P that the expanding root system and mycorrhiza hyphal network had access to from the soil volume ; (4) trees were sufficient in nutrient content and otherwise well-watered and fertilized with other macronutrients and micronutrients ; or (5) soil-water status and nutrient availability in the low P-fixing Candler fine sand was not as restrictive to diffusion and mass flow of P as might be expected in finer textured soils of higher buffering capacity. The second possibility is supported by studies that indicate benomyl inhibited P uptake, transport and possibly transfer through the plantmycorrhizal fungus interface (Sukarno et al, 1993(Sukarno et al, , 1996, but benomyl did not reduce fungal alkaline phosphatase activity of G. caledonium colonizing cucumber (Larsen et al, 1996). This raises the possibility that different mycorrhizal species in the soil population vary in their sensitivity to benomyl.…”

“…This reduction in P acquisition had no negative effect on growth of trees because tissue P status never dropped below the critical level of leaf P for citrus (0n10 %) during this 27-month study. Adequate P status of citrus trees was maintained with or without P fertilization and despite benomyl inhibition of extraradical and intraradical activity of mycorrhizas (Hale & Sanders, 1982 ;Larsen et al, 1996 ;Sukarno, Smith & Scott, 1993. There are several possible reasons to explain why trees did develop P deficiency : (1) trees were planted from the commercial nursery with stored P ( 0n20 % leaf P) that was re-allocated for growth ; (2) root systems had pre-established mycorrhizal colonization when transplanted, and even though further development and activity was inhibited by benomyl, some mycorrhizal-mediated uptake of P occurred even at low P supply ; (3) slow-growing perennial Citrus on the four rootstocks had a relatively low P demand compared with supply of P that the expanding root system and mycorrhiza hyphal network had access to from the soil volume ; (4) trees were sufficient in nutrient content and otherwise well-watered and fertilized with other macronutrients and micronutrients ; or (5) soil-water status and nutrient availability in the low P-fixing Candler fine sand was not as restrictive to diffusion and mass flow of P as might be expected in finer textured soils of higher buffering capacity.…”

The effect of fungicides on vesicular–arbuscular mycorrhizal symbiosis. III. The influence of VA mycorrhiza on phytotoxic effects following application of fosetyl‐Al and phosphonate

“…We have shown that fosetyl-Al reduced growth of both nonmycorrhizal and mycorrhizal Allium cepa, with the roots becoming markedly stunted (Sukarno, Smith & Scott, 1993). One possible explanation was Al toxicity, which is well known to reduce root growth, particularly in soils of low pH.…”

“…This was presumed to be due to accumulation of phosphonate as well as phosphate, although the method used (Bartlett, 1959) could not discriminate between these two forms of P. Recovery of mycorrhizal plants was suggested to be due to a greater ability to convert phosphonate to phosphate, although this was not tested (Sukarno et al, 1993). This paper describes a more detailed investigation into the effects of fosetyl-Al and its degradation products, phosphonate and Al, on growth of nonmycorrhizal and mycorrhizal plants.…”

Survival of propagules of arbuscular mycorrhizal fungi in soils in eastern Australia used to grow cotton

“…Every 4 wk for 32 wk four cores of soil collected from Narrabri in 1995 were examined for viable hyphae using the method of Sukarno, Smith & Scott (1993). A 3-g subsample was taken from each core and placed in 200 ml of 2 % Calgon® solution, mixed for 5 min and four 2-ml aliquots taken and passed through a 8-/*m nitrocellulose filter (Millipore).…”