In northwestern Spain, where weather is rainy and mild throughout the year, Fusarium verticillioides is the most prevalent fungus in kernels and a significant risk of fumonisin contamination has been exposed. In this study, detailed information about environmental and maize genotypic factors affecting F. verticillioides infection, fungal growth and fumonisin content in maize kernels was obtained in order to establish control points to reduce fumonisin contamination. Evaluations were conducted in a total of 36 environments and factorial regression analyses were performed to determine the contribution of each factor to variability among environments, genotypes, and genotype × environment interactions for F. verticillioides infection, fungal growth and fumonisin content. Flowering and kernel drying were the most critical periods throughout the growing season for F. verticillioides infection and fumonisin contamination. Around flowering, wetter and cooler conditions limited F. verticillioides infection and growth, and high temperatures increased fumonisin contents. During kernel drying, increased damaged kernels favored fungal growth, and higher ear damage by corn borers and hard rainfall favored fumonisin accumulation. Later planting dates and especially earlier harvest dates reduced the risk of fumonisin contamination, possibly due to reduced incidence of insects and accumulation of rainfall during the kernel drying period. The use of maize varieties resistant to Sitotroga cerealella, with good husk coverage and non-excessive pericarp thickness could also be useful to reduce fumonisin contamination of maize kernels.

Alternative approaches to linkage and association mapping using inbred panels may allow further insights into loci involved in resistance to Fusarium ear rot and lead to the discovery of suitable markers for breeding programs. Here, the suitability of a maize multiparent advanced-generation intercross population for detecting quantitative trait loci (QTLs) associated with Fusarium ear rot resistance was evaluated and found to be valuable in uncovering genomic regions containing resistance-associated loci in temperate materials. In total, 13 putative minor QTLs were located over all of the chromosomes, except chromosome 5, and frequencies of favorable alleles for resistance to Fusarium ear rot were, in general, high. These findings corroborated the quantitative characteristic of resistance to Fusarium ear rot in which many loci have small additive effects. Present and previous results indicate that crucial regions such as 210 to 220 Mb in chromosome 3 and 166 to 173 Mb in chromosome 7 (B73-RefGen-v2) contain QTLs for Fusarium ear rot resistance and fumonisin content.

Contamination of maize with fumonisins depends on the environmental conditions; the maize resistance to contamination and the interaction between both factors. Although the effect of environmental factors is a determinant for establishing the risk of kernel contamination in a region, there is sufficient genetic variability among maize to develop resistance to fumonisin contamination and to breed varieties with contamination at safe levels. In addition, ascertaining which environmental factors are the most important in a region will allow the implementation of risk monitoring programs and suitable cultural practices to reduce the impact of such environmental variables. The current paper reviews all works done to address the influence of environmental variables on fumonisin accumulation, the genetics of maize resistance to fumonisin accumulation, and the search for the biochemical and/or structural mechanisms of the maize plant that could be involved in resistance to fumonisin contamination. We also explore the outcomes of breeding programs and risk monitoring of undertaken projects.

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15In Southern Europe where whole maize kernels are ground and used for making bread and other food products, 16 infection of the kernels by Fusarium verticillioides and subsequent fumonisin contamination pose a serious safety 17issue. The influence of environmental factors on this fungal infection and mycotoxin accumulation as the kernel 18 develops has not been fully determined, especially in such food grade maize. The objectives of the present study 19were to determine which environmental factors may contribute to kernel invasion by F. verticillioides and 20 fumonisin accumulation as kernels develop and dry in naturally infected white maize. Three maize hybrids were 21 planted at two different sowing dates and kernel samples were collected 20, 40, 60, 80 and 100 days after silking. 22The percentage of kernels infected, and ergosterol and fumonisin contents were recorded for each sampling. F. 23 verticillioides was the most prevalent species identified as the kernels developed. Temperature and moisture 24 conditions during the first 80 days after silking favored natural kernel infection by F. verticillioides rather than by 25Aspergillus or Penicillium species. Fumonisin was found in kernels as early as 20 days after silking however 26 significant fumonisin accumulation above levels acceptable in the EU did not occur until after physiological 27 maturity of the kernel indicating that kernel drying in the field poses a high risk. Our results suggest that this 28 could be due to increasing kernel damage by insects that favor fungal development, such as the damage by the 29 moth Sitotroga cerealella, and to the occurrence of stress conditions for F. verticillioides growth that could trigger 30 fumonisin biosynthesis, such as exposure to suboptimal temperatures for growth simultaneously with low water 31 activity.

Fusarium poses food and feed safety problems because most species produce mycotoxins. To understand the epidemiology of the Fusarium disease, efforts must focus more precisely on how environmental variables affect disease presence. The objectives of the present study were to monitor the occurrence of Fusarium species in maize kernels in northwestern Spain to determine the risk of mycotoxin contamination and to identify environmental traits affecting the composition of the Fusarium species identified. A combination of 24 environments was evaluated. The percentage of kernels infected by F. verticillioides ranged from 33 to 99%, supporting the idea that fumonisin contamination is the main maize-based feed and food safety concern in this area. In this region, temperature and humidity primarily affected Fusarium spp. occurrence. Warmer temperatures during the later stages of kernel development and during kernel drying increased the frequency of F. verticillioides in maize kernels, while the presence of F. subglutinans was increased by higher relative humidity during the silking stage and cooler temperatures during kernel drying.

The objective of this study was to investigate the stability, across well‐differentiated environments, of genetic control of maize resistance to Fusarium graminearum and Fusarium verticillioides ear rots and mycotoxin contamination, found in genotypes of diverse origin and adapted to different environments. This knowledge will help to design the most appropriate breeding programme to reduce mycotoxin content across a wide range of environments. Although maize genetics involved in resistance to ear rots and mycotoxin contamination greatly depended on the environment, additive and dominance effects were the predominant genetic effects in most environments. The stability across environments for resistance to ear rots and deoxynivalenol and fumonisin contamination was low, and recommended target areas of breeding programmes for either Fusarium species are different based on the different nature of genetic effect × environment interactions for each species. In general, the classification of inbreds and hybrids according to their resistance levels was similar across environments, suggesting that the same sources of resistance could be suitable for different environments, and breeding for resistance to one species would affect resistance to the other one.

Background: Plant breeding has been proposed as one of the most effective and environmentally safe methods to control fungal infection and to reduce fumonisin accumulation. However, conventional breeding can be hampered by the complex genetic architecture of resistance to fumonisin accumulation and marker-assisted selection is proposed as an efficient alternative. In the current study, GWAS has been performed for the first time for detecting high-resolution QTL for resistance to fumonisin accumulation in maize kernels complementing published GWAS results for Fusarium ear rot. Results: Thirty-nine SNPs significantly associated with resistance to fumonisin accumulation in maize kernels were found and clustered into 17 QTL. Novel QTLs for fumonisin content would be at bins 3.02, 5.02, 7.05 and 8.07. Genes with annotated functions probably implicated in resistance to pathogens based on previous studies have been highlighted. Conclusions: Breeding approaches to fix favorable functional variants for genes implicated in maize immune response signaling may be especially useful to reduce kernel contamination with fumonisins without significantly interfering in mycelia development and growth and, consequently, in the beneficial endophytic behavior of Fusarium verticillioides.