Water activity and temperature effects on growth of Alternaria arborescens on tomato medium

Interacting Abiotic Factors Affect Growth and Mycotoxin Production Profiles of Alternaria Section Alternaria Strains on Chickpea-Based Media

Chickpea is susceptible to fungal infection and mycotoxin contamination. Argentina exports most of its chickpea production; thus, its quality is of concern. The Alternaria fungal genus was found to be prevalent in chickpea samples from Argentina. The species within this genus are able to produce mycotoxins, such as alternariol (AOH), alternariol monomethyl ether (AME), and tenuazonic acid (TA). In this context, we evaluated the effect of water activity (0.99, 0.98, 0.96, 0.95, 0.94, 0.92, and 0.90 a_W), temperature (4, 15, 25, and 30 °C), incubation time (7, 14, 21, and 28 days), and their interactions on mycelial growth and AOH, AME, and TA production on chickpea-based medium by two A. alternata strains and one A. arborescens strain isolated from chickpea in Argentina. Maximum growth rates were obtained at the highest a_W (0.99) and 25 °C, with growth decreasing as the a_W of the medium and the temperature were reduced. A. arborescens grew significantly faster than A. alternata. Mycotoxin production was affected by both variables (a_W and temperature), and the pattern obtained was dependent on the strains/species evaluated. In general, both A. alternata strains produced maximum amounts of AOH and AME at 30 °C and 0.99-0.98 a_W, while for TA production, both strains behaved completely differently (maximum levels at 25 °C and 0.96 a_W for one strain and 30 °C and 0.98 a_W for the other). A. arborescens produced maximum amounts of the three toxins at 25 °C and 0.98 a_W. Temperature and a_W conditions for mycotoxin production were slightly narrower than those for growth. Temperature and a_W conditions assayed are those found during chickpea grain development in the field, and also could be present during storage. This study provides useful data on the conditions representing a risk for contamination of chickpea by Alternaria toxins.

Quantifying the Role of Ground Beetles for the Dispersal of Fusarium and Alternaria Fungi in Agricultural Landscapes

The spread by arthropods (zoochory) is an essential dispersal mechanism for many microorganisms, like plant pathogens. Carabid beetles are very abundant and mobile ground-dwelling insects. However, their role in the dispersal of economically relevant phytopathogens, like Fusarium and Alternaria fungi is basically unknown. We quantified the total fungal, Fusarium, and Alternaria load of carabid species collected in the transition zones between small water bodies and wheat fields by screening (i) their body surface for fungal propagules with a culture-dependent method and (ii) their entire bodies for fungal DNA with a qPCR approach. The analysis of entire bodies detects fungal DNA in all carabid beetles but Alternaria DNA in 98% of them. We found that 74% of the carabids carried fungal propagules on the body surface, of which only half (49%) carried Fusarium propagules. We identified eight Fusarium and four Alternaria species on the body surface; F. culmorum was dominant. The fungal, Fusarium and Alternaria, load differed significantly between the carabid species and was positively affected by the body size and weight of the carabids. Carabid beetles reveal a remarkable potential to disseminate different fungi. Dispersal by ground-dwelling arthropods could affect the spatial-temporal patterns of plant disease and microorganisms in general.

Production of Alternaria Toxins in Yellow Peach (Amygdalus persica) upon Artificial Inoculation with Alternaria alternate

The yellow peach (Amygdalus persica), an important fruit in China, is highly susceptible to infection by Alternaria sp., leading to potential health risks and economic losses. In the current study, firstly, yellow peaches were artificially inoculated with Alternariaalternate. Then, the fruits were stored at 4 °C and 28 °C to simulate the current storage conditions that consumers use, and the Alternaria toxins (ATs) contents from different parts of the fruits were analyzed via ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The results showed that the growth of A. alternate and the ATs production were dramatically affected by the storage temperature. At 28 °C, the fungi grew rapidly and the lesion diameter reached about 4.0 cm within 15 days of inoculation, while, at 4 °C, the fungal growth was noticeably inhibited, with no significant change in the lesion diameter. To our surprise, high contents of ATs were produced under both storage conditions even though the fungal growth was suppressed. With an increase in the incubation time, the amounts of ATs showed a steady tendency to increase in most cases. Remarkably, alternariol monomethyl ether (AME), alternariol (AOH), and tenuazonic acid (TeA) were detected in the rotten tissue and also in the surrounding tissue, while a large amount of TeA could also be found in the healthy tissue. To the best of our knowledge, this is the first report regarding the production of ATs by the infection of Alternaria sp. in yellow peach fruits via artificial inoculation under regulated conditions, and, based on the evidence herein, it is recommended that ATs be included in monitoring and control programs of yellow peach management and food safety administration.

Understanding the effect of postharvest tomato temperatures on two toxigenic Alternaria spp. strains: growth, mycotoxins and cell-wall integrity-related gene expression

BACKGROUND

Tomato fruit is susceptible to Alternaria spp. spoilage. Correct postharvest management is necessary to prevent mold growth and mycotoxin accumulation, temperature being one of the main factors associated with these problems. The effect of different postharvest temperatures (5, 12, 25, and 35 °C) on growth, mycotoxin production, and stress-related gene expression by two Alternaria spp. was assessed.

RESULTS

Growth rates decreased rapidly when temperature was higher than the optimum (25 °C), while a gradual reduction was detected at lower temperatures. Tenuazonic acid (TeA) was strongly synthesized at all the temperatures that were evaluated, with a maximum between 12 and 25 °C. Alternariol monomethyl ether (AME) was produced only at the two lowest temperatures, with a peak at 12 °C. Regarding the expression of the stress-related RHO1 gene, during active fungal growth both Alternaria spp. showed more copies of the gene as temperature increased. At the stationary phase, RHO1 gene expression was significantly higher at 12 °C, coinciding with the highest accumulation of AME.

CONCLUSION

Changes in temperature related to different postharvest stages of tomato fruits markedly affect toxigenic Alternaria spp. The highest levels of both mycotoxins were recorded at 12 °C, a common storage temperature for tomato fruit. An association between alternariol biosynthesis and the cell wall integrity pathway was also noticed in relation to temperature, suggesting that temperature may act as a stressor stimulating the RHO1 gene expression, which in turn triggers this mycotoxin synthesis. These results will be useful in developing new strategies to control Alternaria spoilage efficiently in tomato fruit and by-products. © 2019 Society of Chemical Industry.

Influence of environmental factors on tenuazonic acid production by Epicoccum sorghinum: An integrative approach of field and laboratory conditions

Sorghum is the fifth most cultivated and consumed grain in the world. However, this grain is frequently contaminated with toxins from fungi. The present study evaluated the effects of environmental factors on tenuazonic acid (TeA) production by Epicoccum sorghinum in the field and in controlled laboratory conditions. In this study, 50 sorghum grain samples were collected from summer and autumn growing seasons and analyzed for TeA contamination using LC-MS/MS. To further understand the ecophysiology of this fungus, an isolated strain of E. sorghinum from the field was investigated for its development and TeA production under controlled environmental conditions in the laboratory. In the ecophysiological investigation, the effects of water activity (0.90, 0.95, 0.99) and temperature (18, 22, 26 and 30 °C) were evaluated on the radial growth, enzymatic production and expression of TAS1, which is the gene involved in TeA production. Results showed that in the field, the summer season presented the highest TeA average level in the grains (587.8 μg/kg) compared to level found in the autumn (440.5 μg/kg). The ecophysiological investigation confirmed that E. sorghinum produces more actively TeA under environmental conditions simulating the summer season. Optimum growth, maximum TAS1 gene expression, and higher extracellular enzymatic production were observed at 26 °C with a water activity of 0.99. Pearson correlation analyses showed that the production of TeA highly correlates with fungal growth. The present study demonstrates that abiotic factors in a combined approach of field and laboratory conditions will assist in predicting the driving environmental factors that could affect growth of E. sorghinum and TeA production in sorghum grains.

Evaluation of Alternaria mycotoxins in strawberries: quantification and storage condition

Alternariol (AOH), alternariol methyl ether (AME) and tentoxin (TEN) are Alternaria mycotoxins produced by the most common post-harvest pathogens of fruits. The production of these metabolites depends on several environmental factors, mainly temperature, water activity, pH and the technological treatments that have been applied to the product. In this study, the occurrence of AOH, AME and TEN was evaluated in strawberries samples stored at different temperatures ranges (at 22 ± 2 or 6 ± 2°C) and different periods (up to 1 month) simulating the current practice of consumer's storage conditions. Sample extraction was performed using a liquid-liquid extraction method prior to LC-MS/MS analysis. AOH was the most prevalent mycotoxins with a 42% at strawberries stored at (22 ± 2)°C and 37% stored at (6 ± 2)°C. The highest AOH levels were found in samples conserved at (22 ± 2)°C ranging between 26 and 752 ng g(-1). AME levels ranged between 11 and 137 ng g(-)(1), which were found mainly in stored samples at (6 ± 2)°C for more than 28 days. None sample presented levels of TEN in either of the studied conditions.