| Fusarium head blight or wheat scab, caused by Fusarium graminearum (teleomorph Gibberella zeae (Schew) Petch), has been the most important disease of wheat, barley and corn in China. Head blight not only causes the severe grain yield loss, but also causes the harvested grain contaminated with several mycotoxins, such as deoxynivalenol (DON) and zearalenone (ZEN). The consumption of food product made from grains contaminated with these toxins is a potential problem for human and farm animals, which is known to cause carcinogenic, genotoxic acute or chronic diseases or to directly target the kidney, liver or immune system, and has caused great concern of food safety. However, the related studies on mycotoxins are fairly few, and the mycotoxin is not under regular detection in China. Therefore, it is necessary to study the characteristics of mycotoxin production, to improve the method of mycotoxin detection, furthermore to provide consumers with general information of mycotoxin contamination of agri-products and foods.Wheat grains were sampled from different wheat planting areas in China, including Fujian, Jiangsu, Sichuan, Henan and Heilongjiang provinces. Fifteen isolates of causal fungi from infected grains were purified and all were identified as F. graminearum with their morphological and molecular information, indicating that F. graminearum was the prevalent fungal species causing wheat scab in China. Among these isolates, toxin-production level was compared using enzyme-linked immunosorbent assay (ELISA) and it was revealed that there was obvious difference of toxin level within 6 isolates which produced conidia well, and 1 high toxin producing isolate was found.To explore the feasibility of mycotoxin detection by developing ELISA based on single chain variable fragment (scFv) of antibody, studies on conjugation of mycotoxin DON, ZEN with horseradish peroxidase (HRP) were conducted. Conjugates of both DON-HRP and ZEN-HRP kept the toxin antigenity and the HRP activity, suggesting they were feasible in application of ELISA kit development after more improvement.DON and ZEN of 55 wheat samples collected from different wheat planting areas in China were assayed with ELISA kit (Neogen Corp, USA). DON was detected ranging in 0.1-5.2ppm in 37 samples with 17 samples over 1ppm, the allowable limit of China National Food and Drug Standard. However, only 29 samples were contaminated with ZEN at fairly low amount of 0.3-228ppb, and there were 3 samples over 100ppb, the allowable limit of China National Food and Drug Standard. From the results, we also found that the samples which had high disease grain rate had high toxin contents; and vice versa, revealing that degree of disease and toxin contents were positively correlated. Moreover, DON contents in most wheat samples were much higher than ZEN contents, which showed that DON was the primary toxin produced by F. graminearum.In a summary, our study will facilitate screening scab-resistant wheat mutant and evaluating resistance of varieties with mycotoxin, and also make it possible to develop an easier ELISA kit based on scFv to detect mycotoxin at a lower cost. |
