Soil microbial communities are involved in the maintenance of productivity and health of agricultural systems; therefore an adequate understanding of soil biodiversity plays a key role in ensuring sustainable use of soil. In the present study, we evaluated the influence of different cropping systems on the biodiversity of the soil bacterial communities, based on a 54-year field experiment established in Martonvásár, Hungary. Terminal restriction fragment length polymorphism (T-RFLP) fingerprinting technique was used to assess soil bacterial diversity and community structure in maize monoculture and three different crop rotations (maize–alfalfa, maize–wheat and the maize–barley–peas–wheat Norfolk type). No differences in richness and diversity were detected between maize monoculture and crop rotations except for the most intense rotation system (Norfolk-type). Although the principal component analysis did not reveal a clear separation between maize monoculture and the other rotation systems, the pairwise tests of analysis of similarity (ANOSIM) revealed that there are significant differences in the composition of bacterial communities between the maize monoculture and maize–alfalfa rotation as well as between wheat–maize and Norfolk-type rotation.

The association between terrestrial plants and arbuscular mycorrhizal (AM) fungi is one of the most common and widespread mutualistic plant-fungi interaction. AM fungi are of beneficial effects on the water and nutrient uptake of plants and increase plant defense mechanisms to alleviate different stresses. The aim of this study was to determine the level of polyphenol oxidase (PPO), guaiacol peroxidase (POX) and glutathione S-transferase (GST) enzyme activities and to track the expression of glutathione S-transferase (GST) gene in plant-arbuscular mycorrhizal system under temperature- and mechanical stress conditions. Our results suggest that induced tolerance of mycorrhizal sunflower to high temperature may be attributed to the induction of GST, POX and PPO enzyme activities as well as to the elevated expression of GST. However, the degree of tolerance of the plant is significantly influenced by the age which is probably justified by the energy considerations.

In this study, root exudates from mycorrhizal and non-mycorrhizal plants growing at low or high nutrient supply were used in vitro to examine their effects on the growth and fumonisin B1 gene (FUM1) expression of Fusarium proliferatum (Hypocreales: Nectriaceae). After one day of exposure to root exudates originating from non-mycorrhizal and low nutrient supply treatment, a significant change in the growth of F. proliferatum was measured, which then equalized after 5 days of incubation. Aside from the fumonisin gene (FUM1) gene, the expression of the mitogen-activated protein kinase gene (HOG1) was also studied using quantitative real-time polymerase chain reaction (qRT-PCR). After 5 days of incubation, mycorrhizal root exudates significantly reduced the expression of the FUM1 gene, irrespective of the extent of the nutrient supplement and colonization level of the target plant. Similar trends in the expressions of FUM1 and HOG1 genes found in our experiment suggest that arbuscular mycorrhizal fungal colonization did not only affect directly the growth and mycotoxin production of F. proliferatum, but also modulated indirectly a number of other mechanisms. Mycorrhizal inoculation showed potential as a biological control agent in the suppression of fumonisin production by F. proliferatum.