Fusarium Ear Rot Symptoms Research Articles

Sexual reproduction parameters in Fusarium verticillioides populations from maize in Brazil

Fusarium verticillioides is an important plant pathogen causing infections on ears and/or stalks of maize. This study aimed to compare sexual reproduction parameters in populations of F. verticillioides from distinct regions in the different Brazilian climatic zones where maize is grown. Fertility and effective population size were calculated from data generated by crossing field isolates with female fertile testers. Three hundred fungi isolates were obtained from maize kernels with Fusarium ear rot symptoms in different geographic regions of Brazil in the years 2012 and 2013. For the entire population, 231 out of 300 isolates were cross-fertile with tester isolates. MAT1–1 and MAT1–2 idiomorphs of the fertile isolates segregated in a 105:126 ratio. Female isolates (hermaphrodites) accounted for 96 out of 231 fertile isolates, while 135 were male-only isolates. The ratio of mating types within the population [Ne(mt)] was 99% of the count for the Brazilian population when the mating type idiomorphs were used as predictors to estimate the population size. However, when this calculation was made on the basis of the female fertile isolates, the Ne(f) was 83%. When the total population was divided by geographical/climatic regions, the frequencies of female fertile isolates were 33 out of 80 fertile isolates from the Northeast (equatorial tropical climate); 49 out of 73 fertile isolates from the Central-West (tropical climate); and only 14 out of 78 fertile isolates from the South (temperate climate), indicating that the sexual reproduction in F. verticillioides is likely favored by a tropical climate in Brazil. Brazilian populations of F. verticillioides show high fertility and high effective population size, suggesting the possibility of frequent sexual reproduction in the field, especially in populations from Tropical Climate regions of Brazil.

Pathogenicity and toxigenicity of Fusarium verticillioides isolates collected from maize roots, stems and ears in South Africa

Fusarium verticillioides is most frequently associated with maize in South Africa. It colonises maize roots, stems and ears endophytically and causes diseases such as Fusarium ear rot (FER) and stalk rot. Fusarium verticillioides can produce fumonisins, which are toxic secondary metabolites harmful to humans and animals. It is, however, unknown whether endophytic and pathogenic isolates from distinct maize tissues differ in their ability to cause disease and produce fumonisins. In this study, Fusarium spp. were collected from maize roots, stems and kernels for phylogenetic analysis and the F. verticillioides isolates were subjected to pathogenic and toxigenic comparison. The translation elongation 1-α (TEF1) gene of the isolates was sequenced, and a phylogenetic tree constructed with maximum likelihood (ML) and Bayesian interference (BI) inferred. Fumonisin production of F. verticillioides isolates was determined in vitro and in planta by using high performance liquid chromatography, and virulence of the isolates was determined by silk channel inoculation of maize ears under field conditions. F. verticillioides was the species with the highest number of isolates followed by F. temperatum and then F. subglutinans. Phylogenetic analyses clustered the different Fusarium spp. according to species. Fumonisin production by F. verticillioides isolates varied from 0 to 21.3 mg/kg in vitro, and 0–16.2 mg/kg in planta. All the F. verticillioides isolates produced FER symptoms, including isolates from roots and stems. Fusarium verticillioides isolates in South Africa thus presented a species highly diverse in toxigenicity, but not in virulence. This finding has implications for managing mycotoxins in maize, as visible symptoms might be misleading to the actual toxin level present, for example low level of disease severity might represent high fumonisin levels and vice versa. The high numbers of F. temperatum, also a mycotoxin producer highlights the concern that kernels could be contaminated with more than one mycotoxin. Integrated disease management of not only F. verticillioides but all Fusarium spp. should thus focus strongly on reducing fungal contamination of maize and the detoxification of grain with focus on using regionally adapted maize varieties.

First report of Fusarium temperatum causing ear rot on maize in Italy

A two-year survey (2011-2012) was conducted to determine the population composition of Fusarium species on maize (Zea mays L.) in Lombardy (northern Italy). Maize ears exhibiting typical symptoms of Fusarium ear rot (FER) (about 30%), such as white to pink colored mycelia on the tip or scattered all over the ear, were collected at harvest. Rotted kernels were surface sterilized, rinsed in sterile water, dried and placed on potato dextrose agar (PDA) amended with dichloran and antibiotics. Developed Fusarium colonies were single-spore purified and grown on Spezieller Nahrstoffarmer agar (Leslie and Summerell, 2006). Based on morphological characteristics, 15 Fusarium spp. strains were identified as Fusarium subglutinans. Colonies on PDA showed a cottony aerial mycelium, initially white, becoming pinkish white. No microconidia chains were detected, conidiophores were erect and terminated in one to three phialides. Macroconidia were falcate, three to five septate, with a slightly beaked apical cell and a barely or distinct footlike basal cell. The translation elongation factor-1α (EF-1α) gene was partially sequenced for all the F. subglutinans strains using primers EF1 and EF2 (Scauflaire et al., 2011). BLASTn analysis showed that the nucleotide sequence (673 bp) of one strain (isolate GV2188, GenBank Accession No. KX156836) shared 100% sequence identity with F. temperatum (HM067689), a recently described species closely related to F. subglutinans (Scauflaire et al., 2011). Using silk channel inoculation method, F. temperatum pathogenicity was assessed on 10 maize ears (LG 32.85 hybrid) under greenhouse conditions. After 30 days, FER symptoms, i.e. whitish pink to lavender fungal growth on kernels, were observed only on inoculated ears and not on water controls. Koch's postulates were fulfilled by re-isolating the fungus from infected kernels. To our knowledge, this is the first report of F. temperatum in Italy associated with FER.

Assessing pigmented pericarp of maize kernels as possible source of resistance to fusarium ear rot, Fusarium spp. infection and fumonisin accumulation

One of the purposes of maize genetic improvement is the research of genotypes resistant to fusarium ear rot (FER) and fumonisin accumulation. Flavonoids in the pericarp of the kernels are considered particularly able to reduce the fumonisin accumulation (FUM). The aim of this field study was to assess the effect of flavonoids, associated with anti-insect protection and Fusarium verticillioides inoculation, on FER symptoms and fumonisin contamination in maize kernels. Two isogenic hybrids, one having pigmentation in the pericarp (P1-rr) and the other without it (P1-wr), were compared. P1-rr showed lower values of FER symptoms and FUM contamination than P1-wr only if the anti-insect protection and the F. verticillioides inoculations were applied in combination. Fusarium spp. kernel infection was not influenced by the presence of flavonoids in the pericarp. Artificial F. verticillioides inoculation was more effective than anti-insect protection in enhancing the inhibition activity of flavonoids toward FUM contamination. The interactions between FUM contamination levels and FER ratings were better modeled in the pigmented hybrid than in the unpigmented one. The variable role that the pigment played in kernel defense against FER and FUM indicates that flavonoids alone may not be completely effective in the resistance of fumonisin contamination in maize.

The influence of flavonoids in maize pericarp on fusarium ear rot symptoms and fumonisin accumulation under field conditions

Breeding efforts have been undertaken to increase resistance of maize to fusarium ear rot (FER) and to fumonisin accumulation. Flavonoids in the pericarp of the kernels are considered particularly able to reduce the fumonisin accumulation. The aim of this 2‐year field study was to assess the effect of flavonoids on FER symptoms and fumonisin contamination in maize kernels using two isogenic hybrids, one providing pigmentation in the pericarp (P1‐rr) and the other without it (P1‐wr). FER incidence (FERi), FER severity (FERs), the incidence of infections caused by Fusarium spp. in symptomless kernels (FF) and fumonisin contamination (FUM) were assessed in both hybrids. Significant differences between the two hybrids were detected mainly in 2012 trials where P1‐rr showed lower FERi (P < 0·01), FF (P < 0·05) and FUM (P < 0·1) than P1‐wr. Site, characterized by local temperature and precipitation, played a relevant role in modelling all the measured variables, as its effect was highly significant in both years, whether they were considered individually or altogether. The interaction of hybrid with location was a significant (P < 0·001) source of variation only for FF. FF, together with FERi, was also significantly (P < 0·001) influenced by the interaction of hybrid with year. In general, FUM was more influenced by year and location parameters, such as temperatures during late ripening, than by flavonoid presence in kernel pericarp. The results indicate that flavonoid pigments alone may not be an important component in the resistance of maize to fumonisin accumulation.

First Report of Fusarium Ear Rot of Maize Caused by Fusarium andiyazi in China.

Maize (Zea mays L.) is an important food crop worldwide. Some Fusarium species cause maize ear rot leading to significant yield losses and, for some Fusarium species, potential risk of mycotoxin contamination. In 2013, a survey was conducted to determine the population composition of Fusarium species on maize in Dongyang, Zhejiang Province, China, where about 5% of maize ears in each field were found with reddish-white mold. Symptomatic maize ears were collected from several cultivars including forage corn Zhedan724 and Zhengdan958, sweet corn Chaotian4 and Chaotian135, and waxy corn Heinuo181 and Zhenuoyu6; no association between the disease and maize cultivars was observed. Maize kernels showing a pink or white mold were surface-disinfested with 70% ethanol and 10% sodium hypochlorite, followed by three rinses with sterile distilled water and placed onto potato dextrose agar (PDA). After 3 days of incubation at 25°C in the dark, mycelia were transferred to fresh PDA and purified by the single-spore isolation method (4). Species were identified based on morphological characteristics (2), and sequence analysis of the translation elongation factor-1α (TEF) gene. The results indicated that Fusarium verticillioides Sacc. (84.6%) is the main causal agent of maize ear rot in this region. However, morphological characteristics of two strains (7.7%) from the same field were found to be identical to F. andiyazi Marasas, Rheeder, Lampr., K.A. Zeller & J.F. Leslie. Colonies on PDA showed floccose to powdery mycelium and pale-purple pigmentation. Hyaline and straight or slightly curved macroconidia were observed with 3- to 6-septate and a slightly curved apical cell. Chlamydospores were absent. In order to validate this result, partial translation elongation factor (TEF-1α, 646 bp) gene sequences of isolates were generated (GenBank Accession No. KJ137019) (1). BLASTn analysis of TEF-1α with the GenBank database revealed 99.7% sequence identity to F. andiyazi (JN408195 and JN408196), and much lower (94 to 98%) identity with other Fusarium spp. Thus, both morphological and molecular criteria supported identification of the strains as F. andiyazi. A pathogenicity test was performed on maize cv. Zhengdan958 in a greenhouse. Four days post-silk emergence, a 2-ml conidial suspension (105 macroconidia/ml) of each isolate was injected into each of 10 maize ears through the silk channel. An equal amount of sterile distilled water was injected into 10 ears as a control. Typical Fusarium ear rot symptoms (reddish-white mold), which were observed in the ears inoculated with these strains 20 days after inoculation, were similar to the original symptoms in the sampling sites, and no symptoms were observed on the water control ears. The same fungus was re-isolated from the infected kernels using the method described above. F. andiyazi are the major pathogens of sorghum (2) and also proved to attack maize kernels recently (3). To our knowledge, this is the first report of F. andiyazi causing Fusarium ear rot on maize in China. Further investigation is needed to gain a better understanding of the spatial and temporal dynamics of this new pathogen. Also, the new species must be considered in the development of maize cultivars with broad-based resistance to the pathogens.

First Report of Fusarium temperatum Causing Fusarium Ear Rot on Maize in Northern China.

In China, several diseases of maize (Zea mays L.) including ear rot are caused by Fusarium spp., leading to significant yield losses and potential risk of mycotoxin contamination (2,3). In 2013, a survey was conducted to determine the population composition of Fusarium species on maize ears in Jilin Province. Symptomatic maize ears with pink or white mold were collected and surface disinfested with 70% ethanol and 10% sodium hypochlorite, followed by three rinses with sterile distilled water and placed onto potato dextrose agar (PDA). After 3 days of incubation at 25°C in the dark, newly grown-out mycelia were transferred onto fresh medium and purified by the single-spore isolation method (4). Fusarium spp. were identified by morphological characteristics (2) and sequence analysis of translation elongation factor-1α (TEF) gene (1). A large number of Fusarium spp. were found including F. graminearum species complex and F. verticillioides. In addition, a new species, F. temperatum, recently described in Belgium (2), was also identified. F. temperatum was originally described as F. subglutinans, but a robust polyphasic approach proved it to be a new biological species closely related to F. subglutinans (2). Previous studies had reported ~15% of Fusarium maize ear rot in Jilin was F. subglutinans. In this study, we found both F. subglutinans s. str. and F. temperatum in the proportion of 16.3% and 9.2%, respectively. Similar to previous studies (2), colonies of our strains on PDA were initially white cottony mycelium that become pinkish white. Conidiophores formed abundantly on SNA that were erect, branched, and terminated in 1 to 3 phialides. Microconidia were abundant, hyaline, 0 to 2 septa, obovoid to oval, and not produced in chains. Chlamydospores were absent. Typically macroconidia were falcate, 3 to 5 septate (mostly 4 septate), hyaline with a curved and blunt apical cell and a distinct foot-shaped basal cell. In order to validate this result, partial translation elongation factor (TEF-1α, 629 bp) gene sequences of isolates were generated (GenBank Accession No. KJ137018) (1). BLASTn analysis revealed 100% sequence identity to F. temperatum (HM067690). A pathogenicity test was performed on maize cv. Zhengdan958. Four days after silk emergence, 2 ml conidial suspension (105 macroconidia/ml) of each isolate was injected into each of 10 maize ears through silk channel. Control plants were inoculated with sterile distilled water. Twenty days after inoculation, typical Fusarium ear rot symptoms (reddish-white mold) was observed on inoculated ears and no symptoms were observed on water controls. Koch's postulates were fulfilled by re-isolating the same fungus from the infected seeds. Although F. temperatum was reported to attack maize kernels in southern China where the annual average temperatures are moderately high (3), to our knowledge, this is the first report of F. temperatum causing Fusarium ear rot in northern China, where the winter is long and very cold, the annual average temperature is 4 to 5°C, and the lowest temperature is lower than -35°C. This indicated that F. temperatum was widely distributed in different ecological regions in China. Furthermore, the northeast spring corn region that includes Jinlin is the most important corn belt, with corn production of this region accounting for 42% of the total corn production in China. Therefore, we should pay more attention to the new species in this region and consider them in the development of maize cultivars with broad-based resistance to the pathogens.

Effects of planting date and environmental factors on fusarium ear rot symptoms and fumonisin B1accumulation in maize grown in six North American locations

Fusarium ear rot, primarily caused byFusarium verticillioides,causes losses in grain yield and quality and can result in contamination of grain by mycotoxins, primarily fumonisin B1. Disease severity and fumonisin B1contamination vary considerably among maize‐growing regions and from year to year. A 2 year field study was conducted in six locations in the USA, to evaluate the roles of planting date, maize hybrid, rainfall, temperature and insect pests in the variation in fusarium ear rot symptoms and fumonisin B1contamination. Grain samples were inspected to determine percentage of kernels with fusarium ear rot symptoms, categorized as ‘moulded’ or ‘starburst’; grain was also analysed by ELISA for fumonisin B1. Hybrid and planting date frequently had significant effects (P ≤ 0·05) on fusarium ear rot and fumonisin B1contamination. Earlier planting consistently resulted in lower ear rot severity, fumonisin B1levels and insect damage. Mould symptoms were highly correlated with thrips populations (Frankliniella occidentalis) (r = 0·78) and with fumonisin B1concentration (r = 0·89). The starburst symptom was not as closely correlated with thrips (r = 0·33) or fumonisin B1(r = 0·18). A multiple linear regression model identified highly significant effects on fumonisin B1for thrips, lower average daily precipitation after flowering, and location. These results strengthen the evidence that locations with high populations of ear‐infesting thrips and dry conditions after pollination have an increased risk of fumonisin contamination, and suggest that high fumonisin levels are much more likely in visibly moulded kernels compared to those with ‘starburst’ symptoms.

Associations of planting date, drought stress, and insects with Fusarium ear rot and fumonisin B1 contamination in California maize

Fusarium ear rot, caused by Fusarium verticillioides, is one of the most common diseases of maize, causing yield and quality reductions and contamination of grain by fumonisins and other mycotoxins. Drought stress and various insects have been implicated as factors affecting disease severity. Field studies were conducted to evaluate the interactions and relative influences of drought stress, insect infestation, and planting date upon Fusarium ear rot severity and fumonisin B1 contamination. Three hybrids varying in partial resistance to Fusarium ear rot were sown on three planting dates and subjected to four irrigation regimes to induce differing levels of drought stress. A foliar-spray insecticide treatment was imposed to induce differing levels of insect injury. Populations of thrips (Frankliniella spp.), damage by corn earworm (Helicoverpa zeae), Fusarium ear rot symptoms, and fumonisin B1 levels were assessed. There were significant effects of hybrid, planting date, insecticide treatment, and drought stress on Fusarium ear rot symptoms and fumonisin B1 contamination, and these factors also had significant interacting effects. The most influential factors were hybrid and insecticide treatment, but their effects were influenced by planting date and drought stress. The more resistant hybrids and the insecticide-treated plots consistently had lower Fusarium ear rot severity and fumonisin B1 contamination. Later planting dates typically had higher thrips populations, more Fusarium ear rot, and higher levels of fumonisin B1. Insect activity was significantly correlated with disease severity and fumonisin contamination, and the correlations were strongest for thrips. The results of this study confirm the influence of thrips on Fusarium ear rot severity in California, USA, and also establish a strong association between thrips and fumonisin B1 levels.

Impact of insecticide treatments on Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) and their influence on the mycotoxin contamination of maize kernels

European corn borer (ECB), Ostrinia nubilalis (Hübner), is the main maize pest in Central and Southern Europe and promotes the infection of maize with Fusarium spp., which produce mycotoxins. The objective of this study was to determine the effect of insecticide treatments on ECB damage, Fusarium infection and mycotoxin contamination. The field experiments were performed from 2000 to 2006 in three locations in north-western Italy. At harvest, ears were rated for the incidence and severity of ECB damage and Fusarium ear rot symptoms, and the harvested kernels were analysed for fumonisins and zearalenone. In all the years except 2003, the chemical treatment had a significant effect on ECB incidence and severity. The ear damage was reduced, on average, by 44.1%. Fusarium ear rot and fumonisin contamination were affected by ECB control. The occurrence of the mycotoxin was significantly reduced, on average by 68%. The differences between the treatments were less clear in the year with highest ECB pressure. No significant difference was observed between the different insecticide classes. No relations were detected between the ECB activity and the occurrence of zearalenone. This research indicates that the production of kernels with low fumonisin content may be enhanced by an insecticide treatment against the second ECB generation.

Fumonisins in Maize: Can We Reduce Their Occurrence?

Fumonisins in Maize: Can We Reduce Their Occurrence?

Occurrence of the mycotoxin moniliformin in maize (Zea maysL.) ears infected byFusarium subglutinans(Wollenw. & Reinking) Nelsonet al.

Fusarium subglutinans has been identified as a prevailing pathogen of maize ears in Poland in the seasons 1985-1991. About 95-100% of ears with Fusarium ear rot symptoms were infected by this species. Moniliformin was present in all 57 ears with pink ear rot symptoms examined. Fusarium-damaged kernels contained an average of 130.9 mg/kg of moniliformin, with large differences between individual samples each year--from 4.2 mg/kg to 530 mg/kg.