Physicochemical Characterization and Antimicrobial Activity against Erwinia amylovora, Erwinia vitivora, and Diplodia seriata of a Light Purple Hibiscus syriacus L. Cultivar

Phytochemicals are essential raw materials for the production of formulations that can be helpful in crop protection. In particular, Hibiscus spp., which are often used in traditional medicine, are rich in potential bioactive molecules. This study presents an analysis of the thermal, vibrational, and phytochemical characteristics of a light purple variety of Hibiscus syriacus, using thermal gravimetric and differential scanning calorimetry, Fourier-transform infrared spectroscopy, and gas chromatography-mass spectroscopy techniques. Further, with a view to its valorization, the antimicrobial activity of its extracts has been investigated in vitro against Erwinia amylovora (the phytopathogen responsible for fire blight in apples, pears, and some other members of the family Rosaceae), Erwinia vitivora (the causal agent of the “maladie d’Oléron” in grapevines), and Diplodia seriata (responsible for “Bot canker”). Higher heating values and thermal features showed similarities with kenaf biomass. The main compounds identified in the hydro-methanolic extracts were: in flowers, 1-heptacosanol, heptacosane, 1-tetracosanol, hexadecenoic acid, 9,12,15-octadecatrienoic acid, and 9,12-octadecadienoic acid; and in leaves, the coumarin derivative 4,4,6,8-tetramethyl-2-chromanone, vitamin E, phytol, and sitosterol. MIC values of 500 and 375 μg·mL−1 were obtained against E. amylovora for flower and leaf extracts, respectively, upon conjugation with chitosan oligomers (to improve solubility and bioavailability). In the case of E. vitivora, MIC values of 250 and 500 μg·mL−1, respectively, were registered. Regarding the antifungal activity, EC90 values of 975.8 and 603.5 μg·mL−1, respectively, were found. These findings suggest that H. syriacus (cv. ‘Mathilde’) may be a promising source of antimicrobials for agriculture.

Characterization and Antimicrobial Activity of a Halophyte from the Asturian Coast (Spain): Limonium binervosum (G.E.Sm.) C.E.Salmon

The work presented herein deals with the characterization and valorization of a halophyte from the cliffs of the Asturian coast: Limonium binervosum (G.E.Sm.) C.E.Salmon (rock sea-lavender). Its biomass and hydromethanolic extracts were studied by elemental and thermal analysis, infrared spectroscopy and gas chromatography–mass spectroscopy. Tetradecanoic acid/esters and 1,2-tetradecanediol were identified in its flower extract, while the leaf extract was rich in linolenic and linoleic acids and their esters, hexadecanoic acid and its esters, and phytol. Both flower and leaf hydromethanolic extracts contained eicosane, sitosterol and tocopherols in significant amounts. With a view to its valorization, the antimicrobial activity of these extracts was investigated against three apple tree and grapevine phytopathogens. Both the hydroalcoholic extracts and their main constituents, alone or in combination with chitosan oligomers (COS), were tested in vitro. A remarkable antibacterial activity was observed for the conjugated complexes of the flower extract with COS, both against Xylophilus ampelinus (MIC = 250 μg·mL−1) and Erwinia amylovora (MIC = 500 μg·mL−1), and complete inhibition of the mycelial growth of Diplodia seriata was found at concentrations <1000 μg·mL−1. In view of these results, this extremophile plant can be put forward as a promising source of bioactive metabolites.

Diplodia seriata (grapevine trunk disease).

Diplodia seriata is a cosmopolitan and plurivorous fungal species occurring on woody hosts belonging to many plant genera and families (Punithalingam and Waller, 1973; Phillips et al., 2007; Slippers et al., 2007). The fungus is encountered in many habitats, but has a primarily temperate distribution and is present on most continents. D. seriata causes canker, dieback, fruit rot and leaf spot diseases on economically important forest and horticultural species (Farr and Rossman, 2020). Reports of the virulence of this pathogen vary depending upon the crop, varieties and hosts involved and it is often regarded as a stress-related pathogen taking advantage of weak or stressed plants. In common with other members of the Botryosphaeriaceae, D. seriata is capable of living endophytically inside plants (Crous et al., 2006; Slippers and Wingfield, 2007) and latent infections of fruits can result in storage rots. The pathogen is dispersed through both pycnidia and ascospores with conidia regarded as the most important inoculum source for short-distance spread. Infection is through wounds, natural openings, or direct penetration of the host tissue. There is no evidence that this species is seedborne although some members of the Botryosphaeriaceae have been shown to be present in seeds (Gure et al., 2005). The extensive host range of this species means that it is more likely to become established in new areas, as establishment will not depend on the presence of specific hosts. The widespread distribution of this species is presumably as a result of the word-wide movement agricultural, forestry and ornamental plants.

Diplodia seriata (grapevine trunk disease).

Diplodia seriata is a cosmopolitan and plurivorous fungal species occurring on woody hosts belonging to many plant genera and families (Punithalingam and Waller, 1973; Phillips et al., 2007; Slippers et al., 2007). The fungus is encountered in many habitats, but has a primarily temperate distribution and is present on most continents.D. seriata causes canker, dieback, fruit rot and leaf spot diseases on economically important forest and horticultural species (Farr and Rossman, 2020). Reports of the virulence of this pathogen vary depending upon the crop, varieties and hosts involved and it is often regarded as a stress-related pathogen taking advantage of weak or stressed plants. In common with other members of the Botryosphaeriaceae, D. seriata is capable of living endophytically inside plants (Crous et al., 2006; Slippers and Wingfield, 2007) and latent infections of fruits can result in storage rots. The pathogen is dispersed through both pycnidia and ascospores with conidia regarded as the most important inoculum source for short-distance spread. Infection is through wounds, natural openings, or direct penetration of the host tissue. There is no evidence that this species is seedborne although some members of the Botryosphaeriaceae have been shown to be present in seeds (Gure et al., 2005). The extensive host range of this species means that it is more likely to become established in new areas, as establishment will not depend on the presence of specific hosts. The widespread distribution of this species is presumably as a result of the word-wide movement agricultural, forestry and ornamental plants.

Production of Phytotoxic Metabolites by Botryosphaeriaceae in Naturally Infected and Artificially Inoculated Grapevines

Grapevine trunk diseases (GTDs) are considered a serious problem to viticulture worldwide. Several GTD fungal pathogens produce phytotoxic metabolites (PMs) that were hypothesized to migrate to the foliage where they cause distinct symptoms. The role of PMs in the expression of Botryosphaeria dieback (BD) symptoms in naturally infected and artificially inoculated wood using molecular and analytical chemistry techniques was investigated. Wood samples from field vines naturally infected with BD and one-year-old vines inoculated with Diplodia seriata, Spencermartinsia viticola and Dothiorella vidmadera were analysed by cultural isolations, quantitative PCR (qPCR) and targeted LC-MS/MS to detect three PMs: (R)-mellein, protocatechuic acid and spencertoxin. (R)-mellein was detected in symptomatic naturally infected wood and vines artificially inoculated with D. seriata but was absent in all non-symptomatic wood. The amount of (R)-mellein detected was correlated with the amount of pathogen DNA detected by qPCR. Protocatechuic acid and spencertoxin were absent in all inoculated wood samples. (R)-mellein may be produced by the pathogen during infection to break down the wood, however it was not translocated into other parts of the vine. The foliar symptoms previously reported in vineyards may be due to a combination of PMs produced and climatic and physiological factors that require further investigation.

Transcriptome Analysis and Cell Morphology of Vitis rupestris Cells to Botryosphaeria Dieback Pathogen Diplodia seriata

Diplodia seriata, one of the major causal agents of Botryosphaeria dieback, spreads worldwide, causing cankers, leaf spots and fruit black rot in grapevine. Vitis rupestris is an American wild grapevine widely used for resistance and rootstock breeding and was found to be highly resistant to Botryosphaeria dieback. The defense responses of V. rupestris to D. seriata 98.1 were analyzed by RNA-seq in this study. There were 1365 differentially expressed genes (DEGs) annotated with Gene Ontology (GO) and enriched by the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The DEGs could be allocated to the flavonoid biosynthesis pathway and the plant–pathogen interaction pathway. Among them, 53 DEGs were transcription factors (TFs). The expression levels of 12 genes were further verified by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). The aggregation of proteins on the plasma membrane, formation variations in the cytoskeleton and plasmodesmata and hormone regulations revealed a declined physiological status in V. rupestris suspension cells after incubation with the culture filtrates of D. seriata 98.1. This study provides insights into the molecular mechanisms in grapevine cells’ response to D. seriata 98.1, which will be valuable for the control of Botryosphaeria dieback.

The influence of water deficit stress on the grapevine trunk disease pathogens Eutypa lata and Diplodia seriata

The increasing prevalence of the grapevine trunk diseases Eutypa and Botryopshaeria dieback has been attributed, in part, to abiotic stresses imposed on vineyards as production intensifies worldwide. The aim of this study was to evaluate the influence of water deficit irrigation practices on the infection of pruning wounds by Eutypa lata and Diplodia seriata, and the subsequent rate of colonisation. Two vineyard trials were conducted over 2 years in South Australia, one in the Riverland using ‘Cabernet Sauvignon’ with four irrigation treatments (100, 50, 25 and 12.5% of the standard irrigation program) and another in the Barossa Valley using ‘Shiraz’ on six rootstocks and own roots, either irrigated or not irrigated. According to leaf water potential assessments, vines with reduced irrigation were generally in water deficit, and therefore subjected to stress. On the whole, incidence of wound infection and distance of colonisation were similar among irrigation treatments for both pathogens, except in the Riverland, where E. lata colonized canes to a greater extent in well-watered vines than those in water deficit. Only vines on rootstock ‘Ramsey’ in the Barossa Valley had greater extent of colonisation by E. lata in the non-irrigated vines. There was no correlation between internal staining and colonisation, with both pathogens recovered up to nearly 20 cm ahead of the staining. Water deficit did not increase the susceptibility of grapevine pruning wounds to infection, nor colonisation of the subtending tissue by E. lata and D. seriata. In fact, there was evidence of decreased susceptibility to colonisation by E. lata in vines subjected to severe water deficit.