Fusarium Verticillioides Isolates Research Articles

Genetic diversity and PCR-based identification of potential fumonisin-producing Fusarium verticillioides isolates infecting corn in the Philippines

Genetic diversity and identification of fumonisin-producing isolates of Fusarium verticillioides from two provinces in the Philippines were analyzed using molecular techniques. Using a Polymerase Chain Reaction (PCR)-based technique, 49 of the 54 isolates were identified as F. verticillioides, with an amplified product of 800 bp using VERT-1 and VERT-2 primers. Of these, VERTF-1/VERTF-2 primers detected 38 fumonisin-producing F. verticillioides isolates producing a single fragment of 400 bp. The other five isolates, which had previously been identified as F. verticillioides by TEF sequences, morphology and sexual crosses, were negative using this method. Using Universally Primed-PCR (UP-PCR) markers for F. verticillioides, no grouping was observed based on geographical origin and species, but intermediate (53.8%) to high (99.6%) bootstrap values and high genotypic diversity (H=0.99) were generated, suggesting that all isolates clearly belonged to F. verticilliodes. Unweighted Pair Group Method with Arithmetic Mean (UPGMA) cluster analysis with Jaccard's coefficient showed that similarities among F. verticillioides isolates were intermediate at 71% similarity level.

EndophyticFusarium verticillioides reduces disease severity caused byUstilago maydison maize

Endophytic fungi represent diverse taxa that inhabit plant hosts without causing disease symptoms. We used endophytic isolates of Fusarium verticillioides (Sacc.) Nirenberg to understand how endophytic fungi interact with pathogens, in this case, the corn smut pathogen, Ustilago maydis DC (Corda). Endophytic F. verticillioides strains were inoculated onto maize seedlings before, simultaneously, or after inoculation with U. maydis, and the effects on smut disease severity and on plant growth were assessed. When F. verticillioides is simultaneously coinoculated with U. maydis, smut disease severity is significantly decreased and plant growth is increased, compared with other treatments. Controls show that F. verticillioides by itself does not have measurable effects on plant growth. Together, our results suggest that a commonly occurring fungal endophyte on maize, F. verticillioides, ameliorates the effects of a host-specific pathogen, U. maydis, by interfering with the early infection process and limiting disease development, resulting in increased plant growth.

Genetic diversity of Fusarium verticillioides isolates from maize in Iran based on vegetative compatibility grouping.

SUMMARY Genetic diversity among Fusarium verticillioides isolates was analyzed using vegetative compatibility groups (VCGs). Forty-four isolates of F. verticilliodes from stalks and seeds were recovered in maize-producing areas in Iran during 2004-2005. Chlorate-resistant nitrate non-utilizing (nit) mutants were recovered from selected isolates of F. verticillioides and used in complementation (heterokaryon) tests. Vegetative compatibility tests by pairing nit mutants identified 25 VCGs among 44 isolates. Twenty-one isolates belonged to single-member VCGs and the remaining 23 isolates belonged to four multimember VCGs. VCG1 was the largest group and included 17 isolates, whereas the other three multimember VCGs contained two isolates each. It is concluded that natural populations of F. verticillioides in Iran are genetically highly divergent and include isolates representing a potential risk for disease development. rot. Fusarium verticillioides (Sacc.) Nirenberg [Gibberella fujikuroi (Sawada) Wollenw., mating population A], a prevalent pathogen of agriculturally important crops

Natural Occurrence of Fusarium Species, Fumonisin Production by Toxigenic Strains, and Concentrations of Fumonisins B1 and B2 in Conventional and Organic Maize Grown in Spain

Sixty samples of corn from both conventional and organic farms were tested for internal fungal contamination. Molds were identified to genus, and those belonging to the genus Fusarium were identified to species. Twenty isolates of Fusarium verticillioides were tested with a high-performance liquid chromatography–naphthalene dicarboxaldehyde–fluorescence method for their ability to produce fumonisins B1 and B2. The internal fungal infection in organic maize (63.20%) was significantly higher than that in conventional maize (40.27%) (P < 0.05). However, the distribution of fungal genera indicated a significantly higher prevalence of Fusarium in conventional (34.93%) than in organic (18.15%) maize, making Fusarium the predominant fungus in conventional maize. This difference in mold distribution between organic and conventional maize was attributed to the difference in cultivation system. The dominant Fusarium species in both conventional and organic samples was F. verticillioides. There were no significant differences in the ability of 20 selected isolates of F. verticillioides to produce fumonisins on conventional or organic corn. Up to 13.3% of the conventional corn samples contained fumonisins B1 and B2 at mean concentrations of 43 and 22 ng/g, respectively. Organic corn samples had somewhat lower levels of contamination: 35 ng/g fumonisin B1 and 19 ng/g fumonisin B2 (P > 0.05). The organic farming system, with well-balanced crop rotation, tillage, and compost fertilization, produced corn that was less likely to be contaminated with Fusarium species, although no significant difference in fumonisin concentrations was found between the two types of contaminated corn.

Pathogenicity and diversity of vegetative compatibility of Fusarium verticillioides

Pathogenicity of 10 Fusarium verticillioides isolates, originated from grain of wheat (five isolates) and maize (five isolates), were studied under greenhouse conditions. Based on different parameters of the pathogenicity estimate (a scale for % of nonemerged plants, % of survived plants, plant vigour - the growth and dry weight of roots and epicotyls and disease severity) it was determined that all F. verticillioides isolates expressed a different degree of pathogenicity. According to % of nonemerged plants six three and one F. verticillioides isolates expressed low, moderate and high degree of pathogenicity, respectively. All F. verticillioides isolates reduced the plant survival rate and vigour, while the disease severity ranged from 2.0 to 3.54. Two types of nit mutants, nit1 and NitM, were obtained by the use of the method of vegetative compatibility. The frequency of nit1 mutants was greater (58.79%) than the frequency of NitM mutants (5.77%). A total of 10 vegetative compatibility groups (VCGs) of F. verticillioides were established in the complementation tests. These results point out to a high genetic diversity of F. verticillioides population.

Stability of maize resistance to the ear rots caused by Fusarium graminearum and F. verticillioides in Argentinian and Canadian environments

Sources of resistance to Fusarium spp. are needed to develop maize hybrids resistant to the accumulation of fungal mycotoxins in the grain. In a search for resistant germplasm in 1999 and 2000, a set of Argentinian maize populations was evaluated in Ottawa, Canada, for resistance to ear rots after inoculation with local isolates of Fusarium verticillioides and F. graminearum. Sixteen of these populations, varying in observed resistance levels, were re-evaluated in 2003 and 2004 in Pergamino, Argentina, using local isolates of the same fungi. Conidial suspensions of each fungal species were inoculated into the silk channel of primary ears. Disease severity was assessed after physiological maturity using a scale based on the percentage of visibly infected kernels. Genotype effect was more important than genotype-by-fungal species or genotype-by-fungal species-by-environment interaction effects. In addition, disease severity levels associated with each fungal species were positively correlated (P < 0.05) (r = 0.90, r = 0.81, r = 0.87 and r = 0.53, in Ottawa 1999 and 2000, and Pergamino 2003 and 2004, respectively). Populations ARZM 01107, ARZM 07138, ARZM 10041, ARZM 13031, ARZM 16002 and Pora INTA exhibited the highest and most stable resistance to both species. Considering that disease resistance exhibited low specificity to the environment and to the fungal species in evaluations conducted in a wide range of environments and with fungal isolates collected from different hemispheres, the most resistant populations are potential sources of genes for stable resistance to these Fusarium spp.

DNA adduct formation by Fusarium culture extracts: lack of role of fusarin C

Fusarium fungi have been shown to infect corn and other crops worldwide, and have a significant impact on human health through loss of crops or contamination of food with mycotoxins. Isolates of Fusarium fungi from an area of South Africa with high incidence of esophageal cancer have been shown to induce esophageal and liver cancer in rats. Several isolates of Fusarium fungi were grown on corn to determine if genotoxic products were produced. We report the incubation of methanol extracts of Fusarium verticillioides cultures with DNA in the presence of rat liver fractions (S9) resulted in the formation of a unique DNA adduct that was detected by 32P-postlabeling. Fusarin C was purified from cultures of Fusarium verticillioides RRC 415, and was not responsible for the formation of the DNA adduct. Treatment of the methanolic extracts with ultraviolet B radiation reduced the fusarin C content in the extract; however, this had no effect on the formation of the DNA adduct following incubation of the extract with DNA and S9. The unique DNA adduct was formed following the incubation of several Fusarium verticillioides isolates from the US and South Africa, while extracts of cultures of Fusarium graminearium and Fusarium sacchari isolates formed very little of the DNA adduct when incubated with DNA and S9. These data suggest that neither fusarin C nor any of its metabolites are responsible for formation of the DNA adduct, and that an unidentified compound is present in F. verticillioides cultures that forms a DNA adduct, and may be important in the etiology of human esophageal cancer.

Genetic characteristics of Fusarium verticillioides isolates from maize in Costa Rica

Thirty‐nine isolates of Fusarium verticillioides from maize seeds from three regions of Costa Rica were classified on fertility, fumonisin production, vegetative compatibility and pathogenicity. The identity of the isolates was verified by sexual crosses with standard tester strains and by isozyme analysis. Twenty‐three isolates (59%) were mating type A− and 16 (41%) were A+; 29 (74%) were female fertile. The isolates produced high amounts of fumonisin B1 when grown on sterilized maize grits, 32 isolates producing more than 1000 μg g−1, as determined by TLC, and 7 less than 1000 μg g−1. Vegetative compatibility tests by pairing nit mutants identified 34 vegetative compatibility groups (VCGs), of which 29 had one member and 5 had two members. Isolates belonging to the same VCG were obtained from the same seed sample. Two pathogenicity tests with different inoculation methods were performed: on toothpick inoculation of 7‐week‐old maize stalks, 71% of the isolates were pathogenic according to the length of the necrosis formed in the stalk, and on sand inoculation of maize seedlings all the isolates were pathogenic, according to shoot length and dry weight production. Differences in aggressiveness between some of the isolates were recorded. It is concluded that natural populations of F. verticillioides in Costa Rica consist of genetically diverse, highly fertile and pathogenic isolates that represent a potential risk for disease development and fumonisin accumulation in maize crops.

Fumonisins in Maize: Can We Reduce Their Occurrence?

Fumonisins in Maize: Can We Reduce Their Occurrence?