Symbiotic relationships between aggressive Fusarium and Alternaria fungi colonizing oat grain

The mycobiota of cereal grain consist of diverse fungal community among which Fusarium and Alternari a species are the most abundant. In biotic community, the competition and cooperative behavior may impact interspecies interactions. In this paper, we first report significant correlations between abundance of these fungi in oat grain. The symbiotic relationships that were found are of key importance because of mycotoxin production by Alternaria and Fusarium fungi. qPCR was used to measure Fusarium and Alternaria DNA in grain of 21 varieties and breeding lines of oats ( Avena sativa and A. byzantina ) from VIR World Collection (N.I. Vavilov All-Russian Institute of Plant Genetic Resources), and mycotoxin deoxynivalenol (DON) level was evaluated by ELISA test. Gere, Våler, KSI 731/01, KSI 432/08 genotypes appeared to be the most infected by both F. culmorum and Alternaria fungi. The highest amounts of DON (up to 1179 mg/kg) occurred in the grain of the breeding line KSI 432/08, as well as in Belinda and Konkur varieties. Stipler variety was the most resistant to all studied fungi and did not accumulate DON. Oat genotypes characterized by larger grains were more susceptible to fungal infections, whereas those with high husk proportion contained more DON. A high positive correlation between the amounts of DNA of F. culmorum and the Fusarium species able to produce trichothecene mycotoxins (Tri- Fusarium ) was shown ( r = + 0.67, p < 0.001), as well as between F. culmorum DNA level and DON accumulation ( r = + 0.57, p < 0.01). When colonizing the same substrate, aggressive Fusarium species and relatively weak Alternaria pathogens are in symbiotic relationships. In this, we found the significant positive correlations between the amounts of DNA of Alternaria fungi and F. culmorum ( r = + 0.66, p < 0.01), and between DNA level of Alternaria and Tri- Fusarium fungi ( r = + 0.86, p <0.001). In this study, DON produced by F. culmorum had no allelopathic effect on Alternaria fungi. At the same time, any interspecies interactions between Alternaria fungi and F. poae, the most abundant species detected in oat grain, were not found. Undoubtedly, the functions of fungal complexes colonizing plants depend on the parameters of the environment and the relationships evolutionarily developed within natural communities.