Changes in Grape Maturity Induced by Spraying Ethanol

Three different ethanol solutions were sprayed onto Cabernet Sauvignon (Vitis vinifera L.) clusters during the ripening period: 2.5, 5 and 10% by volume in water. Controls were sprayed with water alone. Three different times of spraying were also tested: 8, 10 and 13 weeks post-flowering. One of the observed changes was a lower titratable acidity in grape samples at harvest, when the clusters were sprayed with ethanol at 10 weeks, in comparison with controls. The wines made with grapes treated with ethanol after mid-veraison, had higher ODs at 520 nm than did the controls. This may due to a combined effect of red pigment levels and acidity. In addition, following malolactic fermentation, the acidity levels of wines made with ethanoltreated grapes were slightly higher than those made with the control grapes. Spraying ethanol at 13 weeks post-flowering increased the berry weight by 10% at harvest without decreasing the °Brix value. The corresponding wines had similar degrees of alcohol. This observation was made for the first time in 2001

Detection of demethylation inhibiting fungicide resistance in the grapevine powdery mildew fungus, Uncinula necator

This thesis investigates the sensitivity of Uncinula necator (Schw.) Burr powdery mildew fungus to DMI (Demethylation inhibiting) fungicides in Australian vinyards. Baseline sensitivities were established for two commonly used DMIs (triadimenol and fenarimol) and a PCR-based assay was developed to detect triadimenol resistence in U. necator on infected grapevine material collected from the field. It has shown that since the introduction of DMI fungicides into Australian vineyards, there has been a shift in sensitivity to triadimenol and, to a lesser extent, fenarimol. This will be useful when developing disease management strategies that reduce and delay the development of resistance to DMI fungicides.Thesis (Ph.D.) -- University of Adelaide, Dept. of Applied and Molecular Ecology, 200

Phytotoxic Metabolites Produced by Fungi Involved in Grapevine Trunk Diseases: Progress, Challenges, and Opportunities

Grapevine trunk diseases (GTDs), caused by fungal pathogens, are a serious threat to vineyards worldwide, causing significant yield and economic loss. To date, curative methods are not available for GTDs, and the relationship between the pathogen and symptom expression is poorly understood. Several plant pathologists, molecular biologists, and chemists have been investigating different aspects of the pathogenicity, biochemistry, and chemical ecology of the fungal species involved in GTDs. Many studies have been conducted to investigate virulence factors, including the chemical characterization of phytotoxic metabolites (PMs) that assist fungi in invading and colonizing crops such as grapevines. Moreover, multidisciplinary studies on their role in pathogenicity, symptom development, and plant-pathogen interactions have also been carried out. The aim of the present review is to provide an illustrative overview of the biological and chemical characterization of PMs produced by fungi involved in Eutypa dieback, Esca complex, and Botryosphaeria dieback. Moreover, multidisciplinary investigations on host-pathogen interactions, including those using cutting-edge Omics techniques, will also be reviewed and discussed. Finally, challenges and opportunities in the role of PMs for reliable field diagnosis and control of GTDs in vineyards will also be explored

Isolation of Phytotoxic Phenols and Characterization of a New 5-Hydroxymethyl-2-isopropoxyphenol from Dothiorella vidmadera, a Causal Agent of Grapevine Trunk Disease

Polyphenols were characterized from Dothiorella vidmadera (DAR78993), which was isolated from a grapevine in Australia. In total, six polyphenols were isolated including a new polyphenol characterized by a spectroscopic method (essentially NMR and HR ESIMS) as 5-hydroxymethyl-2-isopropoxyphenol. Tyrosol, benzene-1,2,4-triol, resorcinol, 3-(hydroxymethyl)phenol, and protocatechuic alcohol, the latter being the main metabolite, were also isolated. Although these are already known as naturally occurring compounds in microorganisms and plants, this is the first time they have been isolated from fungal organisms involved in grapevine trunk disease. When assayed on tomato seedlings, all the compounds show similar phytotoxic effects. However, when assayed on grapevine leaves (Vitis vinifera cv Shiraz), resorcinol was the most toxic compound, followed by protocatechuic alcohol and 5-hydroxymethyl-2-isopropoxyphenol

Rapid marker-assisted selection of antifungal Bacillus species from the canola rhizosphere

A marker-assisted approach was adopted to search for Bacillus spp. with potential as biocontrol agents against stem rot disease of canola caused by Sclerotinia sclerotiorum. Bacterial strains were isolated from the rhizosphere of canola and screened using multiplex PCR for the presence of surfactin, iturin A and bacillomycin D peptide synthetase biosynthetic genes. Among the 96 isolates screened, only CS-42 harbored all three genes and was subsequently identified as Bacillus cereus using 16S rRNA gene sequencing. This strain was found to be effective in significantly inhibiting the growth of S. sclerotiorum in vitro and in planta. Scanning electron microscopy studies at the dual culture interaction region revealed that mycelial growth was curtailed in the vicinity of bacterial metabolites. Complete destruction of the outmost melanised rind layer of sclerotia was observed when treated with the bacterium. Transmission electron microscopy of ultrathin sections challenged with CS-42 showed partially vacuolated hyphae as well as degradation of organelles in the sclerotial cells. These findings suggested that genetic marker-assisted selection may provide opportunities for rapid and efficient selection of pathogen-suppressing. Bacillus strains for the development of microbial biopesticides

Biocontrol Potential of an Endophytic Pseudomonas poae Strain against the Grapevine Trunk Disease Pathogen Neofusicoccum luteum and Its Mechanism of Action

Grapevine trunk diseases (GTDs) impact the sustainability of vineyards worldwide and management options are currently limited. Biological control agents (BCAs) may offer a viable alternative for disease control. With an aim to develop an effective biocontrol strategy against the GTD pathogen Neofusicoccum luteum, this study investigated the following: (1) the efficacy of the strains in suppressing the BD pathogen N. luteum in detached canes and potted vines; (2) the ability of a strain of Pseudomonas poae (BCA17) to colonize and persist within grapevine tissues; and (3) the mode of action of BCA17 to antagonize N. luteum. Co-inoculations of the antagonistic bacterial strains with N. luteum revealed that one strain of P. poae (BCA17) suppressed infection by 100% and 80% in detached canes and potted vines, respectively. Stem inoculations of a laboratory-generated rifampicin-resistant strain of BCA17 in potted vines (cv. Shiraz) indicated the bacterial strain could colonize and persist in the grapevine tissues, potentially providing some protection against GTDs for up to 6 months. The bioactive diffusible compounds secreted by BCA17 significantly reduced the spore germination and fungal biomass of N. luteum and the other representative GTD pathogens. Complementary analysis via MALDI-TOF revealed the presence of an unknown cyclic lipopeptide in the bioactive diffusible compounds, which was absent in a non-antagonistic strain of P. poae (JMN13), suggesting this novel lipopeptide may be responsible for the biocontrol activity of the BCA17. Our study provided evidence that P. poae BCA17 is a potential BCA to combat N. luteum, with a potential novel mode of action.This research project was supported by a Charles Sturt University Australian Government Research Training Program (AGRTP) scholarship and a Wine Australia PhD Scholarship (PPA001773).Peer reviewe

Biology and biocontrol of Sclerotinia sclerotiorum (Lib.) de Bary in oilseed Brassicas

Sclerotinia sclerotiorum (Lib.) de Bary is a necrotrophic plant pathogen infecting over 500 host species including oilseed Brassicas. The fungus forms sclerotia which are the asexual resting structures that can survive in the soil for several years and infect host plants by producing ascospores or mycelium. Therefore, disease management is difficult due to the long term survivability of sclerotia. Biological control with antagonistic fungi, including Coniothyrium minitans and Trichoderma spp, has been reported, however, efficacy of these mycoparasites is not consistent in the field. In contrast, a number of bacterial species, such as Pseudomonas and Bacillus display potential antagonism against S. sclerotiorum. More recently, the sclerotia-inhabiting strain Bacillus cereus SC-1, demonstrated potential in reducing stem rot disease incidence of canola both in controlled and natural field conditions via antibiosis. Therefore, biocontrol agents based on bacteria could pave the way for sustainable management of S. sclerotiorum in oilseed cropping systems

Molecular detection and identification of Diatrypaceous airborne spores in Australian vineyards revealed high species diversity between regions.

The grapevine trunk disease, Eutypa dieback (ED), causes significant vine decline and yield reduction. For many years, the fungus Eutypa lata was considered the main pathogen causing ED of grapevines in Australia. Recent studies showed other Diatrypaceous fungi were also associated with vines exhibiting dieback symptoms but there is limited information on how these fungal pathogens spread in vineyards. Thus, information on the spore dispersal patterns of Diatrypaceous fungi in different wine regions will assist in identifying high-risk infection periods in vineyards. Using more than 6800 DNA samples from airborne spores collected from eight wine regions in south-eastern Australia over 8 years using a Burkard spore trap, this study investigated the diversity and abundance of Diatrypaceous species, using multi-faceted molecular tools. A multi-target quantitative PCR (qPCR) assay successfully detected and quantified Diatrypaceous spores from 30% of the total samples with spore numbers and frequency of detection varying between regions and years. The high-resolution melting analysis (HRMA) coupled with DNA sequencing identified seven species, with E. lata being present in seven regions and the most prevalent species in the Adelaide Hills, Barossa Valley and McLaren Vale. Cryptovalsa ampelina and Diatrype stigma were the predominant species in the Clare Valley and Coonawarra, respectively while Eutypella citricola and Eu. microtheca dominated in the Hunter Valley and the Riverina regions. This study represents the first report of D. stigma and Cryptosphaeria multicontinentalis in Australian vineyards. This study further showed rainfall as a primary factor that triggers spore release, however, other weather factors that may influence the spore release in different climatic regions of Australia still requires further investigation

Spencertoxin and spencer acid, new phytotoxic derivatives of diacrylic acid and dipyridinbutan-1,4-diol produced by Spencermartinsia viticola , a causal agent of grapevine Botryosphaeria dieback in Australia

Spencermartinsia viticola is one of the most widespread Botryosphaeriaceae species isolated from grapevines in South Australia and New South Wales vineyards in Australia. A new phytotoxic dipyridine-butane-1,4-diol and a new diacrylic acid derivatives, here named spencertoxin (1) and spencer acid (2), were isolated from the culture filtrates of S. viticola isolate DAR78870 together with p-hydroxybenzaldehyde (3) and 2-(4-hydroxyphenyl) acetic acid (4). Spencertoxin and spencer acid were characterized as 2,3-di(pyridin-3-yl)butane-1,4-diol and (2Z,2′Z)-3,3′-(carbonylbis(oxy))diacrylic acid, respectively, by spectroscopic methods (essentially NMR and HRESIMS). Spencertoxin (1), p-hydroxybenzaldehyde (3) and 2-(4-hydroxyphenyl) acetic acid (4) showed phytotoxicity when the pure compounds were assayed on grapevine leaves of Vitis lambrusca and Vitis vinifera cv. Shiraz. Keywords: Grapevine, Botryosphaeria dieback, Spencermartinsia viticola, Phytotoxins, Spencertoxin and spencer aci

Phytotoxic metabolites by nine species of Botryosphaeriaceae involved in grapevine dieback in Australia and identification of those produced by Diplodia mutila, Diplodia seriata, Neofusicoccum australe and Neofusicoccum luteum

Botryosphaeria dieback is one of the main trunk diseases of grapevine caused by several species of Botryosphaeriaceae. Twenty-four fungal isolates representing the eight most widespread and most virulent Botryosphaeriaceae were tested for their ability to produce phytotoxic metabolites. The chromatographic profiles of their culture filtrates organic extracts showed the ability of all isolates to produce several and different metabolites. When tested on grapevine leaves and tomato cuttings the organic extracts phytotoxicity varied among isolates and species. To our knowledge, this is the first study on phytotoxic compounds produced by Botryosphaeriaceae species found in Australian vineyards. The phytotoxic metabolites produced by Diplodia seriata, Diplodia mutila, Neofusicoccum australe and, for the first time, by Neofusicoccum luteum were isolated and chemically identified essentially by spectroscopic methods