Effects of Moringa oleifera Leaf Extracts on Xanthomonas campestris pv. campestris

Abstract

Xanthomonas campestris pv. campestris (Xcc) is a Gram-negative bacterium belonging to the Xanthomonodaceae family, causing black rot in crucifers. To control this pathogen, the study investigated the effect of different leaves extracts of Moringa oleifera Lam., a tropical plant, well known for its food properties and with countless applications in many different fields, from nutraceutical (hypoglycemic) to the cosmetic (sunscreen) properties. Nevertheless, several studies pointed to its antibacterial action against both Gram-negative and Gram-positive bacteria. Many bioactive compounds, including flavonoids, phenolic acids, alkaloids, isothiocyanates, tannins and saponins, contained in these extracts, are responsible for its countless activities. The analyses carried out in this study show that the methanolic, hydroalcoholic and hydroalcoholic maltodextrin extracts have both bacteriostatic and bactericidal effects at concentrations of 0.5, 0.5 and 0.1 mg/mL respectively. In particular, the study shows how all extracts can alter membrane permeability, to adversely affect swarming motility, and to alter biofilm formation in Xcc. The in planta experiments showed a reduction of the necrosis area in the infected radishes, although the ability of the extracts to be absorbed by root systems is yet to be understood, in order to reach the target point.

Control of Erwinia amylovora Growth by Moringa oleifera Leaf Extracts: In Vitro and in Planta Effects

“…In this case, all extracts seem to act in the same way, reducing biofilm formation by 80%. The main accredited assumption is that certain phenolics (i.e., chlorogenic acid, quercetin, rutin, ellagic acid and others) may act as anti-biofilm compounds [ 24 , 27 ].…”

“…Based on data extracted from the literature and from our previous article, the antimicrobial effect can be attributed to the presence of many polyphenolic compounds, which act in a potentially synergistic manner [ 24 ]. It has been hypothesized that some of these compounds are able to complex at bacterial cell walls, altering fluidity, structure and functionality of the phospholipid double layer, resulting in a stop of ATP synthesis and a consequent slowdown of all ATP-dependent functions; simultaneously, the entrance through the altered membrane of compounds capable of inhibiting the enzyme complexes involved in bacterium replication is promoted [ 33 , 34 , 35 ].…”

“…company. Extraction methods were performed as described in Fontana et al [ 24 ]: Hydroalcoholic extract (HA-MOE): Leaf powder was mixed with hydroalcoholic solution (ethanol:water, 70:30) at room temperature, filtered and concentrated in vacuum. Methanolic extract (MeOH-MOE): Leaf powder was mixed with methanol and subjected to two sonication cycles (40 °C, 60 min, 80%) with subsequent centrifugation and concentrated under vacuum.…”

“…In terms of antimicrobial activity, a number of studies have highlighted this property for different MOEs; i.e., in 2016, it was demonstrated how different extracts from seeds, leaves and roots were able to inhibit Staphylococcus aureus and Streptococcus mutans growth [ 23 ]; as for phytopathogens, our previous study shows how these extracts can inhibit the growth and virulence of different Xanthomonas campestris pv. campestris strains [ 24 ].…”

“…Given the economic impact that the disease causes in many regions, combined with the research of alternative treatments relative to the use of chemicals or antibiotics, we have an ongoing research program (SUSTANIA) aimed to explore the effects of different plant extracts, selected on the basis of their sustainable source and safe design (renewable plant parts, not at risk of extinction, high productivity and possibly used for food or cosmetics). In this context, from our previous research [ 24 , 25 ], we decided to study the effect of various extracts of leaves of M. oleifera Lam. on the virulence factors of EA: in particular, we focused on its in vitro effect on membrane permeability, swarming motility, amylovoran production and biofilm formation; and on in planta preventive and therapeutic effects.…”