Antifungal Activity and Biochemical Profiling of Exudates from Germinating Maize Nostrano di Storo Local Variety

Abstract

Plant pathogens are responsible for important damages to valuable crops causing important economic losses. Agrobiodiversity protection is crucial for the valorization of local varieties that could possess higher resistance to biotic and abiotic stress. At the beginning of germination, seeds are susceptible to pathogens attacks, thus they can release endogenous antimicrobial compounds of different natures in the spermosphere, to contrast proliferation of microorganisms. The work aimed at characterizing the maize of local variety Nostrano di Storo seed exudates secreted during the first phases of germination, to identify compounds active in the defense towards pathogens. Storo seed exudates were proven to inhibit F. verticilloides germination. In order to investigate the cause of the described effect, compositional profiling of the exudates was performed through NMR, lipidomic, and proteomic analyses. This study suggests an important role of microbial endophytic communities in the protection of the seed during the early phases of the germination process and their interplay with fatty acids released by the seeds, rather than a specific antifungal compound. The valorization of agronomically acceptable maize lines with pre-harvest enhanced resistances to pathogens contamination could lead, in the near future, to commercially available varieties potentially requiring more limited chemical protective treatments.

Keywords: NMR; Zea mays; antifungal compound; biodiversity; endophytes; fatty acids; germination; local varieties; plant protection; proteomics.

Figure 1

F. verticilloides conidial germination in presence of 32 h (A) and 72 h. (B) Nostrano di Storo seeds imbibition media. Results are reported as percent of germinated conidia with respect to total conidia ± standard deviation. Statistical differences were assessed with a Student’s T-test * p < 0.05, ** p < 0.01; *** p < 0.001; **** p < 0.0001.

Figure 2

F. verticilloides fungal growth in presence of imbibition media of selected maize local varieties, grown in the same fields (A). Data are reported as % absorbance increase at each timepoint with respect to initial timepoint ± standard deviation. (B) Reports the investigation at closer timepoints of fungal growth in presence of sample H (Nostrano di Storo maize local variety) in comparison with a control sample where the same amount of fungal conidial were incubated without any maize imbibition medium. Statistical significance was assessed with ANOVA test * p < 0.01.

Figure 3

¹H NMR spectra of maize Nostrano di Storo exudate dissolved in D₂O at 25 °C. In the upper panel the spectra related to the first 24 h after imbibition are reported; in the lower panel, the second interval of 24 h after replacing medium (24–48 h) is reported. In the insets are presented the magnifications of the high field regions attributable to aromatic/olefinic compounds (A) and low field regions attributable to aliphatic compounds (B) of the exudate after 24 h of imbibition with the relative magnification power.

Figure 4

Methyl esters fatty acids (FAME) on 32 h Nostrano di Storo seed imbibition medium (A,C) and on ungerminated Nostrano di Storo seeds (B,D). Panel A and B report the relative proportion of the identified FAME, while panels C and D group FAME according to the saturation of the aliphatic chains as Saturated Fatty Acids (SFA); Monounsaturated Fatty Acids (MUFA); ω-6 Polyunsaturated Fatty Acids (N-6 PUFA); ω-3 Poly Unsaturated Fatty Acids (N-3 PUFA).