From laboratory to the field: biological control of Fusarium graminearum on infected maize crop residues.

AIM: To evaluate biological control agents (BCAs) against Fusarium graminearum on infected maize stalks as a means to reduce Fusarium head blight (FHB) in subsequently grown wheat. METHODS AND RESULTS: In the laboratory, BCAs were applied against F. graminearum on maize stalk pieces. Clonostachys rosea inhibited the perithecia development and ascospore discharge when applied before, simultaneously with and after the pathogen. In the field, we simulated a system with high disease pressure, that is, a maize-wheat rotation under no-tillage, by preparing maize stalks inoculated with F. graminearum. The infected stalks were treated with formulations of C. rosea selected in vitro or the commercial BCA strain Trichoderma atrobrunneum ITEM908 and exposed to field conditions over winter and spring between winter wheat rows. Monitoring with spore traps and of FHB symptoms, as well as quantification of F. graminearum incidence and DNA in harvested grain revealed significant reductions by C. rosea by up to 85, 91, 69 and 95% compared with an inoculated but untreated positive control, respectively. Deoxynivalenol (DON) and zearalenone (ZEN) contents were reduced by up to 93 and 98%, respectively. Treatments with T. atrobrunneum were inconsistent, with significant reductions of DON and ZEN under warm and wet climatic conditions only. CONCLUSIONS: The findings support the application of C. rosea against F. graminearum on residues of maize to suppress the primary inoculum of FHB. SIGNIFICANCE AND IMPACT OF THE STUDY: As sustainable agriculture requires solutions to control FHB, hence, the application of C. rosea during the mulching of maize crop residues should be evaluated in on-farm experiments.

The potential of antagonistic fungi for control of Fusarium graminearum and Fusarium crookwellense varies depending on the experimental approach.

AIMS: To investigate the potential of fungal antagonists to control Fusarium head blight (FHB) causing pathogens (Fusarium graminearum and F. crookwellense) with two different experimental approaches. METHODS AND RESULTS: Using two in vitro tests, Clonostachys rosea, Cladosporium cladosporioides and 10 Trichoderma strains were screened. In a co-culture assay, all Trichoderma strains significantly reduced the colony area of F. graminearum and F. crookwellense by 45-93%, whereas C. rosea and C. cladosporioides were not effective. In another assay, all antagonists from a chosen subset reduced the number of perithecia and ascospores on wheat straw by 88-100% when inoculated before the pathogen. Only C. rosea, a weak antagonist in the co-culture assay, was effective when inoculated after the pathogen, reducing perithecia and ascospore production by 73 and 100%, respectively. CONCLUSIONS: For screening antagonists and to avoid sorting out highly effective strains, it is crucial to consider different experimental approaches since the efficacy might differ substantially depending on the incubation conditions. By using two distinct experimental set-ups, we identified promising biological control agents. SIGNIFICANCE AND IMPACT OF THE STUDY: FHB is one of the most devastating fungal cereal diseases worldwide. As the pathogen overwinters on crop residues, application of antagonists on residues of the previous crop during harvest could be a promising approach to efficiently control FHB in cereals as an essential part of an integrated disease management.

Fusarium species complex and mycotoxins in grain maize from maize hybrid trials and from grower's fields.

AIMS: To quantify and to compare the occurrence of Fusarium species in maize kernels and stalk pieces, to analyse mycotoxins in kernels and maize crop residues, to evaluate two approaches to obtain kernel samples and to compare two methods for mycotoxin analyses. METHODS AND RESULTS: The occurrence of Fusarium species in maize kernels and stalk pieces from a three-year maize hybrid trial and 12 kernel samples from grower's fields was assessed. Nine to 16 different Fusarium species were detected in maize kernels and stalks. In kernels, F. graminearum, F. verticillioides and F. proliferatum were the most prevalent species whereas in stalks, they were F. equiseti, F. proliferatum and F. verticillioides. In 2006, 68% of the kernel samples exceeded the recommended limit for pig feed for deoxynivalenol (DON) and 42% for zearalenone (ZON), respectively. Similarly, 75% of the samples from grower's fields exceeded the limits for DON and 50% for ZON. In maize crop residues, toxin concentrations ranged from 2.6 to 15.3 mg kg(-1) for DON and from 0.7 to 7.4 mg kg(-1) for ZON. Both approaches to obtain maize kernel samples were valid, and a strong correlation between mycotoxin analysis using ELISA and LC-MS/MS was found. CONCLUSIONS: The contamination of maize kernels, stalk pieces and remaining crop residues with various mycotoxins could pose a risk not only to animal health but also to the environment. With the hand-picked sample, the entire Fusarium complex can be estimated, whereas combine harvested samples are more representative for the mycotoxin contents in harvested goods. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first multi-year study investigating mycotoxin contamination in maize kernels as well as in crop residues. The results indicate a high need to identify cropping factors influencing the infection of maize by Fusarium species to establish recommendations for growers.