Biochemical aspects of interactions between fungi and plants: A case study of Fusarium in oats

Abstract

Disclosing the mechanisms that build up plant resistance to fungal diseases (pathogenic microorganisms) invariably evokes the need to analyze biochemical factors of resistance. Protective mechanisms are associated with a fairly large number of chemical compounds. Fusarium head blight (FHB) affects cereal grains, including wheat, barley and oats. In this work, we report new data on the metabolic profile of oat grains, as influenced by FHB, and a relationship between plant resistance and content of individual metabolites in FHB-susceptible and FHB-resistant varieties. Here, we have challenged the task to assess the connections of FHB-resistance parameters in oat varieties with as many compounds as possible. Such data are required both to understand the mechanisms of resistance and to develop methods for its assessment. Common oat (Avena sativa L.) varieties from the collection of the Vavilov Institute (VIR) were studied to evaluate their numerous biochemical characters and their resistance to FHB. The fatty acid composition of oil was analyzed by the method of gas-liquid chromatography with mass spectrometry on an Agilent 6850 chromatographer (USA), and other metabolites were quantitated. Plant resistance was studied under artificial infestation of ears with F. culmorum and F. sporotrichioides (an experimental field, All-Russian Research Institute for Plant Protection, St. Petersburg—Pushkin, 2015). Fusarium Link fungi DNA content and trichothecene mycotoxins were determined in milled grain samples. The amount of DNA of Fusarium fungi was measured by real-time PCR techniques using Tri5 gene-based group-specific primers. Solid-phase competitive enzyme-linked immunosorbent assay (ELISA) was used to measure the content of T-2 toxin and DON in grain. The statistical significance of differences in biochemical parameters, including metabolic profiles, between resistant and susceptible oat varieties was estimated with the Mann-Whitney criterion. For the first time, correlations were found between Fusarium resistance and biochemical characteristics of oat. It has been shown that high-protein forms are less affected by FHB, accumulate less toxins, and are more adaptive to biotic stress. Plant resistance to FHB correlates with accumulation of pipecolic acid, monoacylglycegols, tyrosine, galactinol, a number of phytosterols, sugars and adenosine. The values of such correlations and connections between chemical compounds and various parameters of Fusarium resistance identified during the study of oat accessions should be regarded as strictly preliminary, since they are the outcome of only one year of field trials. However, the year in consideration was characterized by extremely favorable conditions for the development of parasitic Fusarium fungi with all immanent consequences. An assumption can be made that the increased aggressiveness of the latter (kind of a model condition) allowed us to identify with more reliability the connections between a majority of metabolite content and composition parameters and the level of Fusarium resistance. Considering the complex polygenic nature of the control over the character “resistance to Fusarium head blight” and, therefore, strong dependence of its expression on the environments, any future efforts to confirm (or refute) our conclusions will require researching greater intra- and interspecies diversity of this crop’s accessions reproduced in various environments and in different years.