Association of L-form Bacteria with Plants and their Application in Biological Control of Phytopathogenic Fungi and Bacteria: A Review

L-form bacteria with modified or no cell walls are a special group of bacteria derived or induced from cell walled forms following suppression of their rigid cell wall. They have been used to establish non-pathogenic symbioses with a wide range of plants. These L-form-plant symbioses have been shown to confer resistance against the subsequent challenge of the associated plants by both fungal and bacterial pathogens. As the world population increases, the demand for food also increases and hence control of plant diseases is of paramount importance in producing enough agricultural crops to fulfil the food demand. Plant disease management using chemical fungicides and pesticides etc. is not an ecofriendly approach and hence researchers look for alternative options such as the use of biocontrol agents which are ecofriendly and sustainable. This review paper highlights the published information on the potential of applying L-form bacteria as a biological control agent in management of plant diseases caused by pathogenic microorganisms.

Zinc(II) complexes of 3,10-C-meso-2,5,5,7,9,12,12,14- octamethyl-1,8-diaza-4,11-diazoniacyclotetradecane as its bis(acetate) trihydrate, [LBH2][CH3COO]2.3H2O: Synthesis, Characterization and antimicrobial studies

One isomeric ligand, LB among three isomers (LA, LB and LC) of 2,9- C-meso-2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclotetradecanes, differing in the orientation of methyl groups on the chiral carbon atoms) on interaction with vinyl acetate produces 2,9-C-meso-2,5,5,7,9,12,12,14- octamethyl-1,8-diaza-4,11-diazoniacyclotetradecane as its bis(acetate) trihydrate, [LBH2][OOCCH3]2.3H2O. This ligand salt trihydrate reacts with Zn(CH3COO)2.2H2O to produce square pyramidal monoacetatozinc(II) acetate complex [ZnLB(CH3COO)](CH3COO), which undergoes anion exchange reaction with NaClO4.6H2O to produce monoacetatozinc(II) perchlorate complex, [ZnLB(CH3COO)](ClO4). The complex, [ZnLB(CH3COO)](ClO4) undergoes axial substitution reactions with KSCN, NaNO2 and KNO3 to form the substitution products, [ZnLB(NCS)](NCS), [ZnLB(NO2)](ClO4) and [ZnLB(NO3)](ClO4) respectively where CH3COOis replaced by NCS- , NO3 - and NO2 - . All these complexes have been characterized on the basis of analytical, spectroscopic, conductometric and magnetochemical data. The antifungal and antibacterial activities of these compounds have been studied against some phytopathogenic fungi and bacteria.

Isoquinoline Alkaloids from Macleaya cordata Active against Plant Microbial Pathogens

Bioassay-guided fractionation of the crude extract of the whole plant of Macleaya cordata R. Br. led to the isolation of four alkaloids, which were identified as sanguinarine (1), chelerythrine (2), protopine (3) and α-allocryptopine (4) on the basis of their physicochemical and spectrometric data. Compounds 1 and 2 demonstrated a significant antifungal activity against the six test fungi with median inhibitory concentrations (IC50) ranging from 0.47 to 6.13 μg/mL. Compound 1 was the most effective with an IC50 of 0.47 μg/mL on Rhizoctonia solani. Furthermore, compounds 1 and 2 also demonstrated strong antibacterial activity, with IC50 values ranging from 5.01 to 11.3 μg/mL, and minimum inhibitory concentrations (MIC) ranging from 8.0 to 32.0 μg/mL. This is the first report on the activity of the alkaloids from M. cordata against economically important phytopathogenic fungi and bacteria.

Bactericidal and Fungicidal Activities of Calia secundiflora (Ort.) Yakovlev

Calia secundiflora (Ortega) Yakovlev (Fabaceae) is considered a medicinal plant in Mexico but has scarcely been used because of the toxicity of its quinolizidine alkaloids. Several quinolizidine alkaloids have shown bactericidal, nematicidal, and fungicidal activities. The purpose of this study was to identify the alkaloids in the seeds and evaluate the activity of the organic extract on several phytopathogenic fungi and bacteria. An in vitro bioassay was conducted with species of the following phytopathogenic fungi: Alternaria solani, Fusarium oxysporum and Monilia fructicola; and of the following bacteria Pseudomonas sp., Xanthomonas campestris and Erwinia carotovora. Cytisine, lupinine, anagyrine, sparteine, N-methylcytisine, 5,6-dehydrolupanine, and lupanine were identified by liquid chromatography-mass spectrometry in the extract of seeds; the most abundant compound of the extract was cytisine. It was observed that the crude extract of Calia secundiflora was moderately active on bacteria and more potent on phytopathogenic fungi. In contrast cytisine showed the opposite effects.

Metabolites from Microsphaeropsis olivacea, an Endophytic Fungus of Pilgerodendron uviferum

Seven compounds belonging to different structural skeletons were isolated from Microsphaeropsis olivacea grown in liquid and solid media. The enalin derivative 7-hydroxy-2,4- dimethyl-3(2H)-benzofuranone is reported for the first time, while additional spectroscopic information is provided for the acetates of botrallin and ulocladol. The activity of the isolated compounds was assessed towards the enzyme acetylcholinesterase (AChE) and their cytotoxicity against human lung fibroblasts. Graphislactone A and botrallin presented a moderate activity towards AChE, with IC50 of 8.1 and 6.1 μg/ml (27 and 19 μᴍ, respectively). Under the same experimental conditions, the IC50 of the standard inhibitor galanthamine was 3 μg/ml. The cytotoxicity of both compounds was > 1000 and 330 μᴍ, respectively. None of the compounds was promising as antibacterial or antifungic against phytopathogenic fungi and bacteria. Botrallin and graphislactone A were detected in the liquid potato-dextrose and yeast extract/ malt extract/dextrose as well as on a solid substrate (rice). Butyrolactone I was obtained from the fungus growing on solid medium.