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.Root exudates were collected from maize plants treated, as described previously, by removing all substrate particles from the roots and then submerging them into 50 mL of 0.01 M L −1 KOH according to da Silva Lima et al. [38]. After 5 min, the root system was washed with tap water, then with Agronomy 2019, 9, 291 3 of 11 distilled water and were incubated in Erlenmeyer flasks filled with 50 mL sterilized distilled water for 24 h. Solutions were sterilized by filtration through 0.22 µm Ø nitrocellulose filters (Millipore, Burlington, MA, USA). Concentrations of root exudates were adjusted to a ratio of 1 g of root fresh weight based on the method of Lioussanne et al. [39]. In this way, the effects of various root exudates remained comparable, however, roots from different treatments showed significant differences in weights. The root exudates were kept at −20 • C until use.
Culture Conditions and Expression Analyses of FUM1 and HOG1 GenesFusarium proliferatum ITEM 2287 (Institute of Sciences of Food Production, CNR, Bari, Italy) was used in the study. Mycelium for fumonisin production was prepared in 50 mL DM (22 mM KH 2 PO 4 , 2.5 mM MgSO 4 , 85 mM NaCl and 117 mM sucrose, pH 5.9) according to Shim and Woloshuk [40], supplemented with 30 mM ammonium dihydrogen phosphate and inoculated with 10 6 mL −1 conidia. Cultures were incubated at 26 • C with shaking (150 rpm) for 48 h then filtrated and washed with sterilized distilled water and mycelium, then transferred directly to 50 mL of new DM medium. The co-cultures were inoculated separately with 5 mL (concentrations adjusted to a ratio of 1 g of root fresh weight) of each of root exudate (+AM LN, −AM LN, +AM HN, −AM HN). The control treatment was prepared by adding 5 mL of sterilized ...