Mycoflora and mycotoxins of peanut (Arachis hypogaea L.) seeds in Egypt. III. Cellulose-decomposing and mycotoxin-producing fungi

From 40 peanut seed samples collected in Egypt, forty-three species and one variety of fungi, belonging to 16 genera, were collected. The most dominant genera were Aspergillus (11 species + one variety), Penicillium (11 species) and Fusarium (4 species). From the preceding genera A. fumigatus, A. flavus, A. niger, P. chrysogenum and F. oxysporum were the most frequent species.Forty-nine isolates belonging to 12 species and one variety were tested for production of mycotoxins, after growth on liquid medium containing two carbon sources (sucrose or cellulose). Thin layer chromatographic analysis revealed that the quality and quantity of mycotoxins was higher on sucrose than cellulose. Mycotoxins identified were aflatoxins B₁, B₂, G₁ & G₂, citrinin; fumagillin; diacetoxyscirpenol T-2 toxin; satratoxin H; and zearalenone.     

重组产毒多杀性巴氏杆菌毒素PMT的N-端和C-端蛋白 的生物学活性及免疫原性

将5个toxA基因片段N1518、C2345、N3172、N3388和C2115分别克隆到合适的原核表达载体pET-28a(b,c)系统,其中pET28a-N1518和pET28b-C2115在大肠杆菌成功表达,获得大小分别为57kDa和78kDa的融合蛋白rPMT-N和rPMT-C,Western blot检测证实两种表达产物均具有反应原性.分别以200μg rPMT-N和rPMT-C对小白鼠进行体内生物学活性试验,结果两种表达蛋白均不能致死小白鼠;体外细胞毒性试验证实896ng/mL的rPMT-N能使Veto细胞发生病变,而rPMT-C对Veto细胞无明显毒性作用.将rPMT-N和rPMT-C制成亚单位疫苗,同时设天然PMT及无菌PBS对照组,间隔2周分2次皮下免疫小白鼠.二免后2周用8.2×105 CFU的HN-13株T Pm进行腹腔攻毒,结果rPMT-N组保护率为90.0%(9/10),rPMT-C组保护率为50.0%(5/10),天然PMT组保护率为80.0%(8/10).综上试验表明,rPMT-N具有良好的生物学活性和免疫原性,可作为PAR疫苗添加成分,显示了良好的应用前景.     

In Vitro Selection for Improved Plant Resistance to Toxin-Producing Pathogens

Simultaneously with the progress in plant biotechnology since the 1980s, new methods in plant pathology have been developed. This review summarizes papers that cover basic research on the effects of selective agents on in vitro cultures of host plants, as well as applications of agents in regeneration systems that result in lines with increased variability in resistance or susceptibility. The first part of the study deals with theoretical aspects of the interactions between plants and toxin‐producing pathogens, mode of phytotoxic action, and host‐ and non‐host‐selective toxins. The second part lists and describes various agents used for selections in vitro. In the last two decades more than 100 publications focused on these selections for the improvement of resistance to plant pathogens. Over 30 plant species were examined to utilise various selection agents extracted from about 40 plant pathogens. The review covers basic research studies and methods that elucidate the relationships between in vitro and in vivo mechanisms of resistance, but also try to develop practical applications to obtain resistant breeding lines. Such methods often utilise some type of explant cultures of the host plants that are treated with various selective agents (culture filtrates, toxins, elicitors), which then elicit typical reactions that parallel those by the pathogens. Their application successfully resulted in resistant lines in banana, carnation, grapevine, strawberry and wheat. Nowadays, these techniques are an important complement to classical breeding methods.     

Fungi associated with food and feed commodities from Ecuador

Freshly harvested soybean, rice and corn from farms and corn-based pelleted feeds were collected from ranches from the coastal and mountain regions in Ecuador during 1998, and assessed for fungal contamination. The most prevalent fungi on pelleted feed were Aspergillus flavus and Fusarium graminearum. The prevalent fungi recovered from soybean were F. verticillioides, F. semitectum, Aspergillus flavus and A. ochraceus. In rice, F. oxysporum was the most prevalent toxigenic fungal species recorded, followed by F. verticillioides and A. flavus. In corn, F. verticillioides was the most prevalent fungus isolated in both the coastal and mountain regions, with high isolation frequencies of A. flavus and A. parasiticus at the coast. Based on the toxigenic species recovered, ochratoxin A may pose a contamination risk for soybean. A higher probability of aflatoxin contamination of corn was found in the coastal samples compared to those of the mountain region, while a risk of fumonisin contamination of corn exists in both regions.This revised version was published online in October 2005 with corrections to the Cover Date.     

Effect of Sowing Time on Toxigenic Fungal Infection and Mycotoxin Contamination of Maize Kernels

Field experiments were set up from 2000 to 2002 in northwest Italy to determine the effects of sowing date on the susceptibility of maize hybrids to ear rot and mycotoxin contamination in natural infection conditions. Three sowing dates (March, April and May) were compared using two hybrids with different maturity classes. The ears were rated for the incidence and severity of disease symptoms at harvest and the harvested kernels were analysed for mycotoxin fumonisin B₁, zearalenone, deoxynivalenol, aflatoxin B₁ and ochratoxin A. The last sowing date resulted in higher values of European corn borer incidence (+39%), kernel Fusarium infection and fungal ear rot severity (increased respectively by a factor of 4 and 3) than the plots sowed in March. The sowing date did not influence the type of mycotoxin found in the kernel, which only depended on the climatic conditions during the season and on their influence on the infection and the development of the fungal species. The natural occurrence of fumonisin B₁ and deoxynivalenol was always significantly higher in late‐sowed plots. A late sowing, after May 10, multiplies the risk of the occurrence of fumonisins and deoxynivalenol in the grains at harvest by a factor of 11.2 and 1.9, respectively. No significant difference was observed for the contamination of zearalenone or aflatoxin B₁ for the different sowing dates. An earlier sowing time than April, resulted in a significant reduction in mycotoxin contamination only in the years in which the meteorological trend protracted the kernel dry down to the autumn months. The use of a late‐maturity hybrid with late sowing, compared with a medium‐maturity hybrid, could lead to a serious risk of mycotoxin contamination. To the authors’ knowledge, this is the first study to report on the effects of sowing time on maize kernel contamination of mycotoxins other than aflatoxins in non‐inoculated conditions.     

A simple procedure for identification ofClostridium botulinum colonies

For direct identification of toxigenic colonies ofClostridium botulinum type E, suspected colonies are uniformly suspended in a phosphate buffer containing 0.5% (w/v) gelatin and 0.05% (w/v) Tween 20. After centrifuging, the supernatant is tested for botulinal toxin by an enzyme-linked immunosorbent assay (ELISA). The assay is specific for this type as it did not react with culture filtrates of otherClostridium species, including non-toxigenic E-like organisms.     

Influence of Growth Stage on Fusarium Head Blight and Deoxynivalenol Production in Wheat

Fusarium head blight is a major concern for wheat production worldwide. The fungi that cause the disease may infect head tissues from flowering to late stages of kernel development, but a better understanding of the influence of the time of infection on grain weight reduction and mycotoxin accumulation resulting from the infection process is needed. We investigated the influence of wheat reproductive stage at the time of inoculation on disease and grain quality parameters, especially production of deoxynivalenol (DON) in mature grains. Heads of Norm wheat were spray inoculated with a macroconidial suspension of a DON‐producing isolate of Fusarium graminearum at each of six reproductive stages from flowering to hard dough. Plants were incubated in a mist chamber for 48 h and then moved to the greenhouse until maturity. Norm wheat was susceptible at all stages inoculated but the highest grain weight reduction and DON accumulation occurred in plants inoculated past flowering to late milk stages. However, high incidences of kernel infection and significant levels of DON accumulation resulted from inoculations as late as the hard dough stage, even though there was no corresponding reduction in grain weight compared to non‐inoculated plants. The occurrence of commercially significant levels of DON in plump, high‐yielding wheat may result from infections that occur during favourable environments well after the flowering stages. Late infection and DON production should therefore be a future research focus for wheat breeding and integrated management of FHB and an important consideration for grading systems that employ the presence of visibly damaged kernels as a means of estimating DON content of wheat.     

Metabolic behaviour of aflatoxin producing strain and non-toxigenic strain of Aspergillus flavus to different sources of nitrogen and glucose concentration

The effect of different nitrogen sources and varying glucose concentration on aflatoxin production by a toxigenic and non-toxigenic strain of Aspergillus flavus was studied. Greatest production (3.8 ppm) of aflatoxin B₁ was produced in a synthetic medium when casamino acids were supplied as the nitrogen source. Optimum sugar concentration for aflatoxin B₁ production ranged between 3 and 10 g/100 ml. There was no appreciable difference in the metabolic behaviour between toxigenic and non-toxigenic strains of A. flavus when dry mycelial weight, total proteins, non-protein nitrogen and reducing sugar were the criteria.     

赤链蛇毒器的发现及离体毒腺的产毒量

本文通过对安徽黄山产赤链蛇毒器的解剖,描述了其毒器的形态、大小和着生位置,并测定了离体毒腺的产毒量。