| Maize ear rot is one of the major disease in the world, which results in severe economic losses, and serves as a potential health risk for humans and animals. Approximately 30 species of fungal are associated with maize ear rot. Fusarium spp. are considered the major causal agents of maize ear rot, which Fusarium verticillioides is more serious. Fumonisins areproduced by F. verticillioides, and can result in birth defects and carcinogenesis. A survey was conducted in 2012 to investigate the contamination of maize by Fusarium species. A total of 250 maize samples were randomly collected from nine provinces(Hebei, Shanxi, Inner Mongilia, Sichuan, Yunnan, Guizhou, Ningxia, Liaoning and Heilongjiang) in China. This study also studied the influence of different effect factors(nitrogen sources, carbon sources, fungicides and chlorogenic acid) on fumonisins produced by F. verticillioides, which had an important significance on controlling maize ear rot. It mainly achieved the following results:1. Fusarium species were isolated and identified using morphological and molecular methods. A total of 2271 Fusarium isolates(20.2%) were obtained from all samples. These isolates included seven Fusarium species, namely, F. graminearum(1121 strains), F. verticillioides(928 strains), F. subglutinans(115 strains), F. proliferatum(92 strains), F. oxysporum(9 strains), F. equiseti(4 strains) and F. chlamydosporum(2 strains).The incidences of Fusarium species in nine provinces were 39.2%(Guizhou), 32.1%(Yunnan), 25.0%(Shanxi), 22.9%(Liaoning), 21.6%(Hebei), 20.0%(Heilongjiang), 16.0%(Sichuan), 9.4%(Ningxia), and 3.8%(Inner Mongolia). F. verticillioides was the dominant species of maize ear rot in Liaoning(17.6%), Sichuan(13.6%), Hebei(11.1%), and Ningxia(6.5%). F. graminearum was the dominant species in Yunnan(26.8%), Guizhou(24.7%)and Shanxi(23.6%). F. subglutinans was the dominant species in Heilongjiang. The percentagesof F.verticillioides, F. subglutinans and F. graminearum were the same in Inner Mongolia.2. Effects of various nitrogen and carbon sources on growth of F. verticillioidesand fumonisins produced by F. verticillioideswere distinguished. In this study, we researched the effects of five nitrogen sources(including beef extract, peptone, sodium nitrate, ammonium sulfate and Glu) and seven carbon sources(including sorbitol, mannitol, sucrose, maltose, glucose, fructose and soluble starch) on mycelialgrowth and fumonisins produced by F. verticillioides. The results indicated that nitrogen sources had a significant influence on the colonial morphology of F. verticillioides, but the carbon sources did not influence the colonial morphology of F. verticillioides. Nitrate nitrogen, mannitol and maltose were the nitrogen source, carbon sources which fitter for mycelia growth of F. verticillioides, respectively; Beef extract, mannitol were fitter for fumonisins produced by F. verticillioides.The content of fumonisins were reduced with the concentration of nitrogen sourcens increased, but were increased with the concentration of carbon sources increased. The changes of p H before and after inoculation on different cultural media were anylazed. The results showed the mycelia growth and accumulation of fumonisins produced by F. verticillioides were inhibited on strong acid conditions, and it was suitable for producing fumonisinson weak acid.3. Fungicides could inhibit the growth of F. verticillioides effectively, but had different effects on fumonisins produced by F. verticillioides. In this study, effects of four fungicides(carbendazim, chlorothalonil, pyraclostrobin and JS300-19) on mycelial growth, germination, fumonisins produced by F. verticillioides and gene expression of FUM1 were studied. Results suggested that all fungicides could inhibit the mycelial growth with EC50 value of 0.41, 1.19, 2.49, 4.22 μg/m L, respectively and inhibit the germination with EC50 value of 3.65, 0.95, 0.94, 0.72 μg/m L, respectively. When F. verticillioides was grown on PDA with fungicides for 6 d, the fumonisins were effectively inhibitted by funigides, while was grown for 10 d, the fumonisins were only inhibited bypyraclostrobin. Other fungicides could inhibit the accumulation of fumonisins when the concentration of fungicides were higher(≥ EC50), as fungicides with lower concentration of(< EC50) could facilitate accumulation of fumonisins. The effects of four fungicides on gene expression of FUM1-the key gene of fumonisins biosynthesis were analyzed using RT-PCR. The results showed gene expression of FUM1 was inhibited by chlorothalonil and JS300-19, but promoted by low concentration of carbendazim and pyraclostrobin, while was inhibited by high concentration.4. Chlorogenic acid had an influence on mycelial growth, germination and accumulation of fumonisins. We studied the effects of chlorogenic acid on mycelial growth, germination and fumonisins of F. verticillioides in vitro. The results showed that chlorogenic acid could inhibit mycelial growth, but facilitate germination. When F. verticillioidsewas grown on PDA with chlorogenic acid for 6 d, fumonisinswere inhibited, and when grown for10 d, fumonisins were facilitated, especially 0.5 mmol/L of chlorogenic acid could strongly facilitate the accumulation of fumonisins. |
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