Systemic Growth of F. graminearum in Wheat Plants and Related Accumulation of Deoxynivalenol

Abstract

Fusarium head blight (FHB) is an important disease of wheat worldwide caused mainly by Fusarium graminearum (syn. Gibberella zeae). This fungus can be highly aggressive and can produce several mycotoxins such as deoxynivalenol (DON), a well known harmful metabolite for humans, animals, and plants. The fungus can survive overwinter on wheat residues and on the soil, and can usually attack the wheat plant at their point of flowering, being able to infect the heads and to contaminate the kernels at the maturity. Contaminated kernels can be sometimes used as seeds for the cultivation of the following year. Poor knowledge on the ability of the strains of F. graminearum occurring on wheat seeds to be transmitted to the plant and to contribute to the final DON contamination of kernels is available. Therefore, this study had the goals of evaluating: (a) the capability of F. graminearum causing FHB of wheat to be transmitted from the seeds or soil to the kernels at maturity and the progress of the fungus within the plant at different growth stages; (b) the levels of DON contamination in both plant tissues and kernels. The study has been carried out for two years in a climatic chamber. The F. gramineraum strain selected for the inoculation was followed within the plant by using Vegetative Compatibility technique, and quantified by Real-Time PCR. Chemical analyses of DON were carried out by using immunoaffinity cleanup and HPLC/UV/DAD. The study showed that F. graminearum originated from seeds or soil can grow systemically in the plant tissues, with the exception of kernels and heads. There seems to be a barrier that inhibits the colonization of the heads by the fungus. High levels of DON and F. graminearum were found in crowns, stems, and straw, whereas low levels of DON and no detectable levels of F. graminearum were found in both heads and kernels. Finally, in all parts of the plant (heads, crowns, and stems at milk and vitreous ripening stages, and straw at vitreous ripening), also the accumulation of significant quantities of DON-3-glucoside (DON-3G), a product of DON glycosylation, was detected, with decreasing levels in straw, crown, stems and kernels. The presence of DON and DON-3G in heads and kernels without the occurrence of F. graminearum may be explained by their water solubility that could facilitate their translocation from stem to heads and kernels. The presence of DON-3G at levels 23 times higher than DON in the heads at milk stage without the occurrence of F. graminearum may indicate that an active glycosylation of DON also occurs in the head tissues. Finally, the high levels of DON accumulated in straws are worrisome since they represent additional sources of mycotoxin for livestock.

Comparative studies about fungal colonization and deoxynivalenol translocation in barley plants inoculated at the base with Fusarium graminearum, Fusarium culmorum and Fusarium pseudograminearum

“…Differently, Covarelli et al (2012) and Winter et al (2013) reported that F. culmorum, in wheat, was unable to colonize the head most likely due to the presence of a lignin layer in the parenchymal cells of the culm. A similar phenomena was described for F. graminearum in durum wheat where the pathogen was not able to reach the head, probably because of a kind of barrier (Moretti et al 2014). …”

“…As already shown in wheat (Mudge et al 2006, Covarelli et al 2012, Winter et al 2013, Moretti et al 2014, FCR is a potential additional source of grain contamination with Fusarium mycotoxins. Thus, the objective of this study was to investigate the ability of F. graminearum, F. culmorum and F. pseudograminearum to systemically colonize barley plants starting from the stem base by visual, scanning electron microscope and Real-Time PCR methods and to verify the possible DON accumulation in the head.…”

“…This finding was also confirmed by SEM observations and is partially in accordance with what described by other authors. The ability of Fusarium species, to systemically move along the stem up to the head, following stem-base infection, was already investigated on soft wheat (Mudge et al 2006, Covarelli et al 2012, Winter et al 2013) and durum wheat (Moretti et al 2014). …”

“…Recently, several studies (Mudge et al 2006, Covarelli et al 2012, Winter et al 2013, Moretti et al 2014, Beccari et al 2018) investigated the colonization process of different Fusarium species and their possible systemic movement along soft and durum wheat plants after stem base inoculation. In particular, Covarelli et al (2012), Winter et al (2013) and Moretti et al (2014), investigating also DON translocation during FCR progress, revealed the presence of this secondary metabolite in wheat heads and in the grains, even when Fusarium was not detected in these parts of the plant. Most of FCR studies were focused on wheat, however, also barley through the years increased its importance, in parallel with the increase of the economic relevance of malt industry with the establishment of new microbreweries, especially in Italy (The Brewers of Europe 2015).…”

Piriformospora indica reduces fusarium head blight disease severity and mycotoxin DON contamination in wheat under UK weather conditions

“…Fusarium culmorum might have produced DON that moved from lower parts of the plants to the heads, consistent with the results of Moretti et al . () and Covarelli et al . () who demonstrated that, although F. graminearum and F. culmorum could not be detected beyond the third internode, a low concentration of DON was found in the kernels beyond those tissues colonized by the fungus, suggesting that DON can be moved from lower parts of the plants to the heads.…”