Impact of ethnic pre-harvest practices on the occurrence of Fusarium verticillioides and fumonisin B1 in maize fields from Vietnam

The occurrence and management of fumonisin contamination across the food production and supply chains

BACKGROUND

Fumonisins (FUMs) are among the most common mycotoxins in plant-derived food products. FUMs contamination has considerably impacted human and animal health, while causing significant economic losses. Hence, management of FUMs contamination in food production and supply chains is needed. The toxicities of FUMs have been widely investigated. FUMs management has been reported and several available strategies have been developed successfully to mitigate FUMs contamination present in foods. However, currently available management of FUMs contamination from different phases of food chains and the mechanisms of some major strategies are not comprehensively summarized.

AIM OF REVIEW

This review comprehensively characterize the occurrence, impacts, and management of FUMs contamination across food production and supply chains. Pre- and post-harvest strategies to prevent FUMs contamination also are reviewed, with an emphasis on the potential applications and the mechanisms of major mitigation strategies. The presence of modified FUMs products and their potential toxic effects are also considered. Importantly, the potential application of biotechnological approaches and emerging technologies are enunciated.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Currently available pre- and post-harvest management of FUMs contamination primarily involves prevention and decontamination. Prevention strategies are mainly based on limiting fungal growth and FUMs biosynthesis. Decontamination strategies are implemented through alkalization, hydrolysis, thermal or chemical transformation, and enzymatic or chemical degradation of FUMs. Concerns have been raised about toxicities of modified FUMs derivatives, which presents challenges for reducing FUMs contamination in foods with conventional methodologies. Integrated prevention and decontamination protocols are recommended to control FUMs contamination across entire value chains in developed countries. In developing countries, several other approaches, including cultivating, introducing Bt maize, simple sorting/cleaning, and dehulling, are suggested. Future studies should focus on biotechnological approaches, emerging technologies, and metagenomic/genomic identification of new degradation enzymes that could allow better opportunities to manage FUMs contamination in the entire food system.

Free and Modified Mycotoxins in Organic and Conventional Oats (Avena sativa L.) Grown in Scotland

Small grain cereals are frequently infected with mycotoxigenic Fusarium fungi. Oats have a particularly high risk of contamination with type A trichothecene mycotoxins; their glucoside conjugates have also been reported. Agronomy practices, cereal variety and weather conditions have been suggested to play a role in Fusarium infection in oats. The current study investigates concentrations of free and conjugated Fusarium mycotoxins in organic and conventional oats grown in Scotland. In 2019, 33 milling oat samples (12 organic, 21 conventional) were collected from farmers across Scotland, together with sample questionnaires. Samples were analysed for 12 mycotoxins (type A trichothecenes T-2-toxin, HT-2-toxin, diacetoxyscirpenol; type B trichothecenes deoxynivalenol, nivalenol; zearalenone and their respective glucosides) using LC-MS/MS. The prevalence of type A trichothecenes T-2/HT-2 was very high (100% of conventional oats, 83% of organic oats), whereas type B trichothecenes were less prevalent, and zearalenone was rarely found. T-2-glucoside and deoxynivalenol-glucoside were the most prevalent conjugated mycotoxins (36 and 33%), and co-occurrence between type A and B trichothecenes were frequently observed (66% of samples). Organic oats were contaminated at significantly lower average concentrations than conventional oats, whereas the effect of weather parameters were not statistically significant. Our results clearly indicate that free and conjugated T-2- and HT-2-toxins pose a major risk to Scottish oat production and that organic production and crop rotation offer potential mitigation strategies.

Public health risk due to aflatoxin and fumonisin contamination in rice in the Mekong Delta, Vietnam

Mycotoxin contamination in rice can lead to a health risk for consumers. In this study, the health risk among different age groups of Vietnamese population in the Mekong Delta, Vietnam was evaluated through rice consumption. Total aflatoxins (AFs) and fumonisins (FBs) in raw rice samples (n = 50) were analyzed using an ELISA method. A survey (n = 155) was used to collect data on rice consumption and consumer practices for the evaluation of mycotoxin exposure. Results showed that the frequency of AFs and FBs contamination was 60 and 74% with the average concentrations in raw rice ranging from 1.88–4.00 ng/g and 227–290 ng/g from the lower bound (LB) to the upper bound (UB), respectively. The average AFs exposure due to rice consumption was estimated from 0.81 to 2.44 ng/kg bw/day at scenarios LB – UB with the medium bound (MB) of 2.10, 1.60, 1.92 and 1.23 ng/kg bw/day for children, adolescents, adults and elderly, respectively. These values ranged from 343 to 724 ng/kg bw/day with respect to FBs (scenarios LB - UB), which are below the provisional maximum tolerable daily intakes (PMTDI) value (2000 ng/kg bw/day). The margin of exposure (MoE) to AFs ranged from 160 to 1585,179-2669,149–2175 and 206–3480 for children, adolescent, adults and elderly, respectively from UB - LB, indicating a high health risk for this carcinogenic hazard since the values are so lower than 10,000 (safe limit). However, for FBs, MoE value ranged from 105 to 575 (UB-LB) for all groups, which are higher compared to 100 (safe limit), indicating no risk for public health. The mean cancer risk due to estimated AFs exposure at LB - UB was 0.05–0.13 cases/year/100,000 individuals with MB of 0.08–0.13 cases/year/100,000 people for all four age groups. This study provides new insights into probabilistic risk assessment and potential health impact of mycotoxins in rice in the Mekong Delta, Vietnam.

Natural Occurrence of Mycotoxins in Maize in North China

Mycotoxins seriously threaten the quality of maize seriously around the world. A total of 426 samples of maize kernel from northeast and northwest China were analyzed in this study. Ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) was performed to analyze the mycotoxin contamination of maize samples. The results showed that it was contaminated by mycotoxins in maize. The average contamination levels of fumonisins, deoxynivalenol, aflatoxins, zearalenone, ochratoxin A, T-2 and HT-2 were 937, 431, 22, 27, 2 and 12 μg/kg, respectively. Concentration of mycotoxins in some samples exceeded their limit, but most were still at safe levels. The contamination level of FBs and DON were most significative. The proportion of mycotoxins exceeding the maximum limit standard was in the following order: 8.0%, 8.0%, 7.0%, 1.6%, 1.4% and 0.0%. The contamination of mycotoxins in maize varies from region to region.

Streptomyces Strains Promote Plant Growth and Induce Resistance Against Fusarium verticillioides via Transient Regulation of Auxin Signaling and Archetypal Defense Pathways in Maize Plants

Driven by climate change, Fusarium ear rot (FER) caused by Fusarium verticillioides occurs frequently in maize worldwide. In parallel, legislative regulations and increasing environmental awareness have spurred research on alternative FER biocontrol strategies. A promising group of bacterial control agents is Streptomyces species due to their metabolic versatility. However, insights into the molecular modes of action of these biocontrol agents are often lacking. This study aims at unraveling the biocontrol efficacy of Streptomyces rhizobacterial strains against F. verticillioides. We first assessed the direct antagonism of four Streptomyces strains ST02, ST03, ST07, and ST08. Then, a profile of 16 genes associated with intrinsic plant defense signaling was assessed in maize plants. Both in vitro and in vivo data showed that the biocontrol strain ST03 perfectly suppressed the growth of F. verticillioides. High inhibition efficacy was also observed for extracellular compounds in the supernatant secreted by this strain. Especially, for maize cobs, the biocontrol strain ST03 not only inhibited the proliferation of F. verticillioides but also significantly repressed fungal fumonisin production 7 days after inoculation. On maize plants, the direct antagonism was confirmed by a significant reduction of the fungal DNA level in soils when co-applied with F. verticillioides and strain ST03. In terms of its action on plants, strain ST03 induced downregulation of auxin responsive genes (AUX1, ARF1, and ARF2) and gibberellic acid (GA)-related gene AN1 even in the absence of F. verticillioides at early time points. In leaves, the biocontrol strain induced the expression of genes related to salicylic acid (SA), and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA)-mediated pathways, and pathogenesis-related proteins in the presence or absence of the pathogen. Interestingly, the biocontrol strain significantly promoted plant growth even in the presence of F. verticillioides. All of which demonstrated that the Streptomyces strain ST03 is a promising FER biocontrol and a growth-promoting candidate.

Impact of Season, Region, and Traditional Agricultural Practices on Aflatoxins and Fumonisins Contamination in the Rice Chain in the Mekong Delta, Vietnam

The current study aimed to evaluate the impact of the crop season, cultivation region, and traditional pre- and post-harvest agricultural practices on mycotoxin contamination in the Mekong Delta rice chain of Vietnam. The results showed that aflatoxins (AFs) and fumonisins (FBs) were predominantly detected in both paddy (n = 91/184, 50%) and white rice (n = 9/46, 20%). Aflatoxin B1 (AFB1)-contaminated paddy samples (n = 3) exceeded the regulatory threshold (5 µg·kg-1). The contamination of paddy with AFs and FBs was not significantly different by growing seasons and cultivation localities. Evidently, in the winter-spring season, fumonisins frequently occurred in paddy planted in Can Tho, while AFs were found in paddy planted in regions Dong Thap and An Giang, and such toxins were absent in Can Tho. Furthermore, the selection of paddy varieties strongly impacted the occurrence of these toxins, especially AFs, for example, line DT8 and Jasmine were susceptible to AFs and FBs. In addition, poor pre- and post-harvest practices (such as crop residue-free fields, fertilizer application, unsanitary means of transport, delayed drying time) had an impact on the AFs and FBs contamination. Our findings can help to understand the dynamics of AFs and FBs in the rice chain in the Vietnamese Mekong Delta, leading to the mitigation of the contamination of AFs and FBs in rice.

Molecular Insights into Defense Responses of Vietnamese Maize Varieties to Fusarium verticillioides Isolates

Fusarium ear rot (FER) caused by Fusarium verticillioides is one of the main fungal diseases in maize worldwide. To develop a pathogen-tailored FER resistant maize line for local implementation, insights into the virulence variability of a residing F. verticillioides population are crucial for developing customized maize varieties, but remain unexplored. Moreover, little information is currently available on the involvement of the archetypal defense pathways in the F. verticillioides-maize interaction using local isolates and germplasm, respectively. Therefore, this study aims to fill these knowledge gaps. We used a collection of 12 F. verticillioides isolates randomly gathered from diseased maize fields in the Vietnamese central highlands. To assess the plant's defense responses against the pathogens, two of the most important maize hybrid genotypes grown in this agro-ecological zone, lines CP888 and Bt/GT NK7328, were used. Based on two assays, a germination and an in-planta assay, we found that line CP888 was more susceptible to the F. verticillioides isolates when compared to line Bt/GT NK7328. Using the most aggressive isolate, we monitored disease severity and gene expression profiles related to biosynthesis pathways of salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA), benzoxazinoids (BXs), and pathogenesis-related proteins (PRs). As a result, a stronger induction of SA, JA, ABA, BXs, and PRs synthesizing genes might be linked to the higher resistance of line Bt/GT NK7328 compared to the susceptible line CP888. All these findings could supply valuable knowledge in the selection of suitable FER resistant lines against the local F. verticllioides population and in the development of new FER resistant germplasms.

Contamination of Fusarium proliferatum and Aspergillus flavus in the Rice Chain Linked to Crop Seasons, Cultivation Regions, and Traditional Agricultural Practices in Mekong Delta, Vietnam

This study evaluates the influence of crop seasons, cultivation regions, and traditional agricultural practices on the occurrence of F. proliferatum and A. flavus in the rice chain in the Mekong Delta, Vietnam. A survey on pre- and post-harvest practices was performed from 2017 to 2019 in parallel with sampling. Results showed that F. proliferatum (36.3%) and A. flavus (10%) were predominantly present throughout the rice chain. These fungi frequently occurred in winter–spring and autumn–winter crops in Can Tho paddy. Especially, F. proliferatum appeared both on the field and during transportation (50–100%), while A. flavus presented at all stages (10–33%). The occurrence of F. proliferatum reduced 70–27% after drying, depended on the seasons, compared to field and transportation stages and could not be detected anymore at further stages. Applying poor pre-harvest agricultural practices such as the use of certain varieties (Jasmine, DT8 varieties), combination of fertilizers (organic–inorganic), fields with crop debris, unhygienic boats, and delayed drying time of 8–12 h or 12–28 h resulted in an increase in fungal contamination on paddy. This study provides a detailed description of fungi contamination in crop seasons, cultivation regions, and agricultural practices, which may help in understanding the fungal dynamic and allow identification of good agricultural practices to mitigate the fungal contamination and potential mycotoxin production.

Post-harvest contamination of maize by Fusarium verticillioides and fumonisins linked to traditional harvest and post-harvest practices: A case study of small-holder farms in Vietnam

Together with conducive climatic factors, poor pre-harvest practices of ethnic small-holder farmers are a major cause of the contamination of maize by Fusarium verticillioides and fumonisins. The proliferation of this field pathogen and the accumulation of its mycotoxins in post-harvest maize caused by ethnic post-harvest practices of subsistence farms have received little attention. Therefore, this study aimed to evaluate the impact of traditional harvest and post-harvest practices on the proliferation of F. verticillioides and fumonisins contamination in post-harvest maize of two ethnic groups: Ede and Kinh from the central highlands of Vietnam. In parallel with analysis, a survey on harvest and post-harvest practices of these farmers was conducted from late December 2017 to early January 2019. As a result, four effective post-harvest practices at mitigating the contamination were defined: (1) removal of damaged cobs at harvest, (2) transport of maize home after harvest, (3) shelling maize away from fields, and (4) drying maize on cement yards. These practices were better implemented by Kinh households than Ede households reducing the post-harvest contamination of maize with F. verticillioides and fumonisin B₁ (FB₁), FB₂, and FB₃. Nevertheless, there is still room for improvement with respect to inadequate open-air drying method, poor storage infrastructure, and poor moisture content management as these correlated to the proliferation of F. verticillioides. Finally, the presence of fumonisins together with aflatoxins in some samples at the storage phase might cause a severe impact on human health.