Comunità fungina dei suoli agrari. Confronto tra due sistemi di conduzione: biologico e convenzionale

Conventional farming using chemical fertilizers and pesticides improved the productivity of crops but caused a decline in soil fertility, an increase in environmental load and the present of pesticide residues in food. Concerns over environmental conservation and consumers perceptions about the safety of public health require the development of organic farming. In agricultural soil, fungi are critical to the maintenance of soil function because their involvement in key processes as: soil structure formation, nutrient cycling, decomposition of organic matter, plant growth promotion, induction of plant resistance. In contrast, other fungi are known to comprise some of the economically most serious plant pathogens especially Fusarium and Aspergillus genus. The aim of this work was to compare the structure of soil fungal communities from organic and conventional management. A particular attention was focused on the mycotoxigenic species and their potential antagonists as Trichoderma and Gliocladium. The employment of this microorganisms to control Fusarium Head Blight (FHB) of wheat appears to be one of the most interesting and promising. FHB can be caused by different pathogens and the most important is Fusarium graminearum, which can strongly reduce the yield and produce mycotoxins. Fungal community were investigated in relation to season, years, site sampling, crop rotation and system management. Mycological cultures allowed the isolation of 99 taxa. Altough the community structure was not statistically affected by different factors considered, 21 taxa were detected only in organic system and 7 taxa were found only in conventional system. MPN analysis results showed that Trichoderma, Fusarium and Aspergillus genus were not significantly affected by different factors. Gliocladium inoculum instead were significantly higher in organic management compared to the conventional one. Eight G. roseum strains isolated from soil samples were screened in dual culture bioassays. Results show that in pathogen-antagonist interactions some F. graminearum are inhibited by G. roseum but none of selected antagonists suppress all tested F. graminearum strains. The only three G. roseum strains shown a minimal inhibitory activity against F. graminearum, were tested against F. verticillioides, F. proliferatum, F. oxysporum, F. solani, F. culmorum and F. sporotrichioides. In this test, G. roseum always reduced the pathogen growth with decreases from 15 to 45% according to strains. G. roseum strains isolated from soil and selected for inhibition tests are scarcely able to carry out biocontrol against F. graminearum but are able to slow the development of others phytopathogenic Fusarium, showing a good biocontrol activity. In summary, our investigation based on 3-years management systems confirm what reported in literature. Soil fungal community was characterized by an elevated homeostasis and short-time effects of different soil managements can be very low. The fungal community structure observed regardless the †œbiological†� value of species was not statistically different between organic and conventional but the organic management was characterized by a higher number of species than conventional. However, it has to be taken into account that the conversion of organic management was made only few years before this study was started. Therefore, the change in fungal community might be a first indicator of shifts in the community to occur some years after the change in agricultural management.