In this study, to evaluate the newly improved technique of the dichlorvos - ammonia (DV-AM) method, AF-producing fungi in an experimental field of Tsukuba were screened. The DV-AM method is the detection technique of the AF-producing fungi by judging from color of the reverse colony: the red (positive) or white (negative), and recently higher sensitivity is achieved by improvement of the nutrient medium composition. Soil samples were collected from 20 spots in an experimental field in July and screened for AF-producing fungi by the improved DV-AM method. As a result, four of positive isolates were isolated from three spot samples from 20 spots. TLC and HPLC assay revealed AF production of all four isolates. The sequence analysis of the calmodulin gene domain and microscopic observation were performed in two of four isolates, which revealed that both strains were Aspergillus flavus. While both were identified as A. flavus, the morphological and physiological characteristics such as production of sclerotia and AF production were different. Thus, the improved DV-AM method was evaluated to detect AF-producing fungi from field soil, and it was also shown that different types of A. flavus strains existed in the same field.
Fusarium species such as Fusarium graminearum infect wheat and barley, and most of them are capable of producing the trichothecene mycotoxins. Trichothecene-contaminated grains cause health hazards to humans and domestic animals. Since wheat and barley commercial cultivars showing strong resistance to Fusarium head blight have not been developed, fungicides have usually been sprayed multiple times on their flowers. The fungicide-resistant strains have been reported. In addition, the pesticides-contaminated grains also affect the human and animal health. Therefore, we try to control Fusarium head blight in cereal crops by utilizing plant-derived metabolites. We found that nicotinamide mononucleotide (NMN), a precursor of nicotinamide adenine dinucleotide (NAD), was highly accumulated in the FHB-resistant barley cultivars. We revealed that NMN acted as a plant defense activator in Arabidopsis. Furthermore, the application of NMN enhanced disease resistance against F. graminearum and suppressed DON mycotoxin accumulation in barley and wheat. We also found that some other compounds such as L-Thr suppressed the trichothecene biosynthesis in F. graminearum. Thus, these metabolites could be useful in controlling disease injury and mycotoxin reduction in cereals.
Pesticides are developed and used for the purpose of improving the productivity of agricultural products and reducing overwork. The development of pesticides with high effects of plant disease caused by funji and reduction of mycotoxins is progressing. It is one of the useful materials to control mycotoxin contamination.
Pesticides residue in food are strictly regulated by establishing Maximum Residue Limit (MRL) based on the Food Sanitation Law. Foods are monitored and instructed in accordance with the law, and the infringing foods are disposed of, and the offender is imprisoned or fined. This MRL has been gradually expanded since it was set in 1968, and the positive list system was introduced in 2006, and all pesticides and foods have been subject to regulation. Since then, due to new development, application expansion, import tolerance, safety evaluation review, etc., MRL values have been added, revised, and deleted one after another.
For students and beginners who learn food-borne fungi, the article describes the conidial formation patterns of Fungi Imperfecti, morphological characteristics of genus Penicillium, and how to use food-borne fungal identification keys.