Multi-Parameter Characterization of Disease-Suppressive Bio-composts from Aromatic Plant Residues Evaluated for Garden Cress (Lepidium sativum L.) Cultivation

Abstract

Garden cress is a vegetable crop in the Brassicaceae family that is appreciated for its nutraceutical and taste-giving components in minimally processed food chains. Due to its very short cycle, which depends on the range of production from microgreens to baby-leaf vegetables, this crop is threatened by soil-borne pathologies developing within the initial stages of germination and emergence. This study aims to evaluate the suppressive bio-compost as an innovative means to counteract the main telluric diseases of garden cress and reduce the risks of yield loss by adopting sustainable remedies and decreasing the dependence on synthetic fungicides. Therefore, eleven green composts obtained using both previously distilled and raw aromatic plant residues were analyzed for suppressive properties against Rhizoctonia solani and Sclerotinia sclerotiorum on sown garden cress. The biological active component of the composts, detected by CO2-release, FDA-hydrolysis and microbial counts, proved to be indispensable for pathogen control in vitro and in vivo, as demonstrated by the loss of suppressiveness after sterilization. Cross-polarization magic angle spinning 13C-nuclear magnetic resonance (CP-MAS-13C-NMR) was used to analyze the molecular distribution of organic C in composts. The results indicated the suitability of the feedstock used to make quality compost. The suppression levels shown by composts P1 (40% wood chips, 30% escarole and 30% a mixture of sage, basil, mint and parsley) and P2 (40% wood chips, 30% escarole and 30% a mixture of essential oil-free sage, basil and rosemary) are promising for the sustainable, non-chemical production of garden cress vegetables.

Evaluation of Sustainable Recycled Products to Increase the Production of Nutraceutical and Antibacterial Molecules in Basil Plants by a Combined Metabolomic Approach

“…The peaks in the O-alkyl-C chemical shift range (60–110 ppm) are assigned to monomeric units of carbohydrates and polysaccharide chains, such as cellulose and hemicellulose of plant tissue. The signals at 61/62 ppm represent the carbon nucleus in position 6, followed by the intense coalescence around 73 ppm formed by the overlapping resonances of carbon 2, 3, and 5, in pyranoside structures, while the most de-shielded peak at 105/6 ppm derives from the di-O-alkyl anomeric carbon in linked glucose units [ 13 , 25 ]. The lower intensity or lack of C resonances at 82 ppm associated to C4 of hexose structures tied through β 1→4 bond ( Figure 1 ), suggest the prevalence of pentose units of hemicellulose as well as the incorporation of oligosaccharides and simple carbohydrates [ 13 , 24 , 25 , 26 ].…”

“…The signals at 61/62 ppm represent the carbon nucleus in position 6, followed by the intense coalescence around 73 ppm formed by the overlapping resonances of carbon 2, 3, and 5, in pyranoside structures, while the most de-shielded peak at 105/6 ppm derives from the di-O-alkyl anomeric carbon in linked glucose units [ 13 , 25 ]. The lower intensity or lack of C resonances at 82 ppm associated to C4 of hexose structures tied through β 1→4 bond ( Figure 1 ), suggest the prevalence of pentose units of hemicellulose as well as the incorporation of oligosaccharides and simple carbohydrates [ 13 , 24 , 25 , 26 ]. Moreover, the high field shift of anomeric C 1 towards 101 ppm in CT samples ( Figure 1 ), further support the preferential solubilization of dissolved low molecular weight sugars not involved in the glycosidic bonds [ 25 ].…”

“…The lowest LigR of CT-COF suggested a preferential accumulation of dissolved phenolic compounds, distinct from lignin-derived molecules, during composting processes of coffee ground wastes and their release in water extracts [ 25 , 29 ]. Conversely, the slight larger LigR ratios shown by HS-COF and CT-ART may be related to a contribution of nitrogenated molecules within the broad bands in the 40–55 ppm NMR region ( Figure 1 ) that indicate the inclusion of peptidic and amino acid moieties [ 13 ].…”

“…For the identification of molecular characteristics, the 13 C-CPMAS-NMR spectra were split into six chemical shift regions: alkyl-C (0–45 ppm); methoxyl-C and N-alkyl-C (45–60 ppm); O-alkyl-C (60–110 ppm); unsubstituted and alkyl-substituted aromatic-C (110–145 ppm); O-substituted aromatic-C (145–160 ppm); carboxyl- and carbonyl-C (160–200 ppm). The structural features of organic materials may be explained and synthesized by dimensionless structural indexes derived from the relative amount of NMR functional groups [ 13 , 25 ]: the hydrophobic index is the ratio of signal intensities of apolar alkyl and aromatic C components over those of hydrophilic C molecules HB/HI = Σ[(0–45) + (45–60)/2 + (110–160)]/Σ[(45–60)/2 + (60–110) + (160–190)]; the aromaticity index compares the number of aromatic compounds to that of the alkyl groups ARM = [(110–160)/Σ(0–45) + (60–110)]; the alkyl ratio is determined by the relative abundance of apolar aliphatic molecules over that of the polar-alkyl fractions A/OA = (0–45)/(60–110); the lignin ratio, relates the area of methoxyl-C and N-alkyl groups to that of O-aryl-C functions LigR = (45–60)/(145–160). …”

“…Therefore, an increasing focus is devoted to sustainable approaches to promote the synthesis of secondary metabolites in aromatic plants thereby preserving the quality of the final products [ 11 ]. In this context, the natural organic fraction obtained from recycled biomasses, such as humic substances (HS) and compost teas (CTs) have been identified as valuable potential abiotic effectors or biostimulants due to their ability to influence directly and indirectly the plant metabolism [ 12 , 13 ]. These molecules can act as bioactive compounds or bioeffectors in various physiological processes, including nutrient up-take, ion transport, enzyme activities, and stress resilience, by promoting appraisable effects on biochemical reactions of primary and secondary metabolism, connected to antibacterial or antioxidant activity and anti-inflammatory action [ 14 , 15 , 16 ].…”