Effect of rare earth application on the growth of Trichoderma spp. and several plant pathogenic fungi

Rare earth elements (REEs) enriched fertilisers are currently used in China for soil and foliar applications to crops, but little is known about the effect of REEs applications on the growth of beneficial and detrimental soilborne microorganisms. The growth of biological control agents Trichoderma atroviride strain P1, Trichoderma harzianum strain A6 and strain T22, plant pathogens Botrytis cinerea, Alternaria alternata, Fusarium solani, Rhizoctonia solani and Sclerotinia sclerotiorum was investigated in the presence of REEs. An in vitro assays was used to monitor the effect of different concentration levels of either a mix of REEs (La, Ce, Pr, Nd) nitrates or lanthanum alone in comparison to treatments conducted with potassium nitrate and water. Although all fungi were affected when the REEs mix or lanthanum were present at concentrations higher than 100 mM, the growth inhibition depended mainly upon the combination of compounds, the dose and the fungal species or strains tested. Trichoderma strains and B. cinerea were more sensitive than A. alternata, F. solani, R. solani or at higher concentrations. Differing growth responses of some fungi to treatments with REEs mix vs. lanthanum alone indicated that in given situations the effect of the REEs compounds may be caused by elements other than lanthanum or by element mixtures. Further investigations are in progress to determine the effect of REEs on important interactions in the soil community between beneficial fungi, pathogenic fungi and/or the plant. REEs are naturally present in the environment and in biological systems but accumulation in soil can take place following successive applications. Therefore, it would be useful to achieve a better understanding of the effect of REEs accumulation on the activity of rhizosphere microorganisms given the widespread use in some regions of rare earths as fertilizers and their presence as fertilizer contaminants.