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

Abstract

This study compares the effects of the fungicide Aliette2 (fosetyl-Al) on non-mycorrhizal and mycorrhizal onion (Allium cepa L.) with effects of the degradation products, aluminium (applied as aluminium chloride) and phosphonate (applied as dimethyl phosphonate). We sought to determine the extent to which the plants absorb and accumulate phosphonate and ascertain why, as shown previously, toxic effects of fosetyl-Al on mycorrhizal plants are less severe than effects on equivalent non-mycorrhizal plants.Fosetyl-Al markedly reduced growth, especially of roots, and also inhibited mycorrhizal colonization. Dimethyl phosphonate caused smaller effects on growth and did not decrease colonization. Aluminium chloride did not affect growth of non-mycorrhizal or mycorrhizal plants, or mycorrhizal colonization. In all cases, mycorrhizal plants grew better than equivalent non-mycorrhizal plants (with no added soil phosphate), and non-mycorrhizal plants given supplementary soil phosphate grew best.Concentrations and contents of total P in shoots were increased by dimethyl phosphonate and more so by fosetyl-Al. Concentrations of P were also increased in roots. $"P nuclear magnetic resonance (NMR) spectroscopy was used to determine relative concentrations of phosphonate and phosphate. Application of fosetyl-Al led to accumulation of more phosphonate than did application of dimethyl phosphonate, and non-mycorrhizal plants treated with fosetyl-Al accumulated much more phosphonate than did equivalent mycorrhizal plants (both with no added soil phosphate). Internal phosphate concentrations increased, especially in mycorrhizal plants, following application of both dimethyl phosphonate and fosetyl-Al. Non-mycorrhizal plants given supplementary soil phosphate also showed restricted growth when treated with fosetyl-Al even though they accumulated phosphate in relatively high amounts and had lower ratios of phosphonate to phosphate, particularly in shoots. In general, high internal concentrations of phosphonate were correlated with large reductions in plant growth among treatments.Possible causes of these effects include conversion of phosphonate to phosphate in the tissues (especially in mycorrhizal plants), enhanced uptake of phosphate via mycorrhizal fungi and additional accumulation of P in plants with restricted growth. Competition for uptake between phosphate and phosphonate is also discussed.

Phosphite and mycorrhizal formation in seedlings of three Australian Myrtaceae

“…Experiments on the effect of phosphite application on monocotyledonous plants with AM are contradictory. For example, Jabahi-Hare and Kendrick (1987) observed an increase in AM in phosphite-treated leek, whereas phosphite decreased AM in maize (Seymour et al 1994) and onion (Sukarno et al 1996(Sukarno et al , 1998.…”

Novel in‐growth core system enables functional studies of grassland mycorrhizal mycelial networks

“…A major barrier to full understanding of the functioning of communities of AM fungal species in soil has been the requirement to eliminate mycorrhizal inoculum from control (nonmycorrhizal) treatments and to date this has only been achieved by sterilization using heat, irradiation or chemical treatments. Of the relatively few studies of AM mycelial functioning that have been undertaken under field conditions or in intact turfs, virtually all have either applied antifungal agents, such as benomyl, fosetyl‐Al or phosphonate (Sukarno et al. , 1998; Jakobsen et al ., 2001) or broad‐spectrum sterilants like methyl bromide (Jakobsen, 1986) to provide the required controls.…”

Exploring mycorrhizal function with NMR spectroscopy

“…31 P NMR has been used by Sukarno et al . (1998) to assess the effects of fungicides on AM symbiosis.…”

“…Xenobiotics and secondary metabolism 31 P NMR has been used by Sukarno et al (1998) to assess the effects of fungicides on AM symbiosis. The study compared the effects of Aliette (fosetyl-Al) on mycorrhizal and nonmycorrhizal onion (Allium cepa) with the effects of the degradation products, Al and phosphonate.…”