No description available.

No description available.

Broccoli head rot is a destructive disease found in most broccoli production areas. The main pathogen is the bacterium Pseudomonas fluorescens. P. fluorescens 5064, which was first isolated from an infected broccoli head in SE Scotland, produces biosurfactants that are important for bacterial establishment on the plant surface prior to causing disease in broccoli. Preliminary experiments performed in this study showed that biosurfactant production in P. fluorescens 5064 was cell density dependent, which is a typical characteristic of the quorum sensing mechanism. Quorum sensing is a bacterial communication mechanism, which controls a number of key processes in growth, reproduction and virulence via signalling molecules (quorum sensing signal) in many gram-negative bacteria. One aim of this study was to determine if biosurfactant production in P. fluorescens 5064 is controlled via quorum sensing. To do this, 35 surfactant-minus Tn5 mutants of P. fluorescens 5064 were screened for their abilities to produce a quorum sensing signal. Six of these biosurfactant-deficient mutants showed a large reduction in quorum sensing signal production. In one mutant 6423, which contains a single Tn5 insertion, the production of the quorum sensing signal was almost eliminated. Addition of quorum sensing signal, either synthetic or extracted from wild type P. fluorescens 5064, was able to restore biosurfactant production in mutant 6423. This strongly suggests that quorum sensing regulates biosurfactant production in P. fluorescens 5064. Attempts were made to clone and sequence the Tn5 disrupted gene in mutant 6423, but the identity of the gene remains inconclusive. The quorum sensing signal in wild type P. fluorescens 5064 was identified in this study by High Pressure Liquid Chromatography and Mass Spectrometry as N-3-hydroxyoctanoyl-homoserine lactone, which has been shown by other researchers to be present in P. fluorescens strain 2-79, but not in the strains F113, 7-14 and NCIMB 10586. The discovery that biosurfactant production in P. fluorescens 5064 is regulated by quorum sensing opens up a possibility for novel control of broccoli head rot. Although only the control of biosurfactant production by quorum sensing was examined in this study, it is possible that other virulence factors, such as pectic enzyme production, are also controlled by quorum sensing as in other pathogenic bacteria. By blocking the quorum sensing system, the pathogenic P. fluorescens that use this mechanism to control virulence could potentially be rendered avirulent. In greenhouse pathogenicity tests, a quorum sensing signal-degrading bacterium, Bacillus sp. A24, was evaluated for biocontrol of head rot disease caused by P. fluorescens 5064 on broccoli. However, the Bacillus sp. A24 showed only limited control effects, despite its strong quorum sensing signal-degrading ability towards the pathogen in vitro. A subsequent test proved that Bacillus sp. A24 is a surfactant producer itself and this could explain its ineffectiveness in disease control. When screening the quorum sensing signals of the 35 biosurfactant mutants, mutant 6418 was found to produce a potent antibiotic-like compound. This was identified by thin-layer chromatography as pyrrolnitrin. Unlike wild-type P. fluorescens 5064, mutant 6418 has lost its ability to produce virulence factors and is thus non-pathogenic. It was therefore of interest to determine if mutant 6418 could be used as a biocontrol agent to control broccoli head rot disease. In greenhouse pathogenicity tests, mutant 6418 significantly reduced disease by 41 %. The practical application of this research to bacterial disease control – via the manipulation of quorum sensing to inhibit virulence gene expression – is discussed.

During the last few years, red raspberry growers in Utah have been finding that plantings gradually lose vigor and are not profitable. In the largest raspberry growing area in Utah, Utah County, figures taken from the U.S. census from 1930 to 1950, show a decrease in acres of raspberries grown from 401 in 1930 to 190 in 1950 (2). In many instances this deterioration of raspberry plantings in Utah has not been definitely associated with known plant pathogenic fungi or virus infections. Neither can the expansion of suburbs account for this decrease. In certain cases it has been obvious that other factors were involved. Since attention had already been directed to above-ground symptoms, the next logical step was to exam in the roots.

Natural organic matter (NOM), a complex mixture of organic compounds, influences drinking water quality and water treatment processes. The presence of NOM is unaesthetic in terms of colour, taste and odour, and may lead to the production of potentially carcinogenic disinfection by-products (DBPs), as well as biofilm formation in drinking water distribution systems. Some NOM removal processes such as coagulation, magnetic ion exchange resin (MIEXTM) and membrane filtration produce sludge and residuals. These concentrated NOM-containing sludges from alum precipitation, membrane treatment plants and MIEX regeneration must therefore be treated prior to disposal. The white-rot fungi possess a non-specific extracellular oxidative enzyme system composed of lignin peroxidase (LiP), manganese-dependent peroxidase (MnP) and laccase (Lac) that allows these organisms to mineralise lignin and a broad range of intractable aromatic xenobiotics. Rojek (2003) has shown the capabi lity of Phanerochaete chrysosporium ATCC 34541 to remove 40-50% NOM from solution, however, this was found to be mainly due to adsorption and to be a partially metabolically linked activity. Consequently, the bioremediation of NOM wastes by selected white-rot fungi was further investigated in the present study. The P. chrysosporium seemed to preferentially remove the very hydrophobic acid (VHA) fraction, and so was most effective for a NOM preparation with a high proportion of hydrophobic content (and so high in colour and specific UV absorbance (SUVA)). The extent of NOM decolourisation by P. chrysosporium in three growth media with different C:N ratios followed the trends: Waksman (C:N = 6) > Fahy (C:N = 76) > Fujita medium (C:N = 114), such that the lower the C:N ratio, the greater NOM removal. This was consistent with the findings of Rojek (2003), who used a different NOM preparation and demonstrated that the removal of NOM increased with decreased C:N ratio (1.58-15.81). As removals of NOM with P. c hrysosporium ATCC 34541 were low, and little biodegradation occurred, this organism was compared with P. chrysosporium strain ATCC 24725, Trametes versicolor ATCC 7731, and three strains of yeast (Saccharomyces species arbitrarily denoted 1, 2 and 3). T. versicolor gave the greatest removal (59%) which was attributed largely to degradation, whereas the NOM removal by the two strains of P. chrysosporium (37%) and the yeast was predominantly due to adsorption as indicated by the deep brown colouration of the biomass. Saccharomyces sp. 1, 2 and 3 removed 12%, 61% and 23% of the colour, respectively. Although Saccharomyces sp. 2 had similar high colour reduction to T. versicolor, the specific removal values differed markedly: 0.055 compared to 0.089 mg NOM/mg biomass, respectively. The low level of the ligninolytic enzymes secreted by both strains of P. chrysosporium corresponded with the low degree of NOM removal by biodegradation as shown by high performance size exclusion chromatography (HPSEC). The high NOM removal attained by T. versicolor was attributed to the activities of the ligninolytic enzymes, especially laccase. The NOM removal was attributed to the breakdown of the high molecular weight compounds to form a pool of low molecular weight materials, which were then most likely utilised by the T. versicolor. Growth of T. versicolor cultures at 36oC caused inhibition or denaturation of the activity of the phenoloxidase enzymes compared to those grown at 30oC. The low activity of LiP in both cultures suggested that this enzyme may not play much of a role in NOM removal. The higher levels of MnP and Lac activities at 30oC were responsible for the greater NOM removal (73% vs. 59%) and thus the cleavage of aromatic rings, conjugated and C-Cβ αbonds in phenolic moieties, as well as catalysing alkyl-aryl cleavage in the NOM structures. T. versicolor cultured in Waksman medium with higher initial glucose (5 g/L cf. 2 g/L) led to lower ligninolytic enzyme activities and a lower degree of NOM removal (25% less colour reduction), probably due to preferential use of glucose over NOM as carbon source. NOM removal (mg removed) increased linearly with NOM concentration up to 600 mg C/L (62 mg (A446); 31 mg (A254)), above which removal decreased markedly. This trend coincided with increasing total ligninolytic enzyme activity, where the level of Lac increased up to 600 mg C/L NOM although MnP decreased gradually across the range while LiP was only detected for 100 and 300 mg C/L NOM. Hence, the removal of NOM from solution by T. versicolor was associated with high oxidative enzyme activity, particularly of laccase. Laccase was the major extracellular enzyme secreted by T. versicolor and by deduction, played a major role in NOM removal. The optimum temperature for Lac activity secreted by T. versicolor cultured in Waksman medium supplemented with 4.5 g/L wheat bran plus 0.5% Tween 80 was determined to be 50oC. The optimum pH for the Lac activity for guaiacol and NOM was identified as pH 4.0-4.5. Although the optimum enzyme activity occurred at 50oC, 30oC was recommended for enzymatic removal of NOM as the phenoloxidase enzyme activity may be denatured if the NOM removal process were considered to run for long period at high temperature. Although agitation led to apparent enzyme denaturation, fermentations with continuous agitation promoted enzyme activity faster than those with occasional agitation (agitated every 6 hours for 30 minutes at 130 rpm and 30oC) as it provides better mass transfer. However, it seemed that continuous agitation had an adverse effect on the fungal growth and enzyme production over extended fermentation periods. Addition of 4.5 g/L wheat bran to modified Waksman medium in the absence of NOM led to high production of Lac activity compared with LiP and MnP activities, showing its great potential as a laccase inducer. Addition of Tween 80 alone to the cultures led to a small improvement in Lac activity; however, with the presence of wheat bran it caused marked increases in LiP, MnP and Lac activit ies. When NOM was added to cultures of T. versicolor with the two supplements, it led to markedly reduced Lac activity, but increased LiP and MnP activities, and no improvement in NOM removal compared with the cultures in the absence of supplements (12 mg (or 61%) cf. 15 mg (or 73%) for 100 mg C/L after corrected for colour from and adsorption by wheat bran).

1. Fusarium roseum �Graminearum� was the predominant fungus associated with stalk rot of maize in eastern Australia in the 1972, 1973 and 1974 growing seasons. All isolates of this pathogen were of the Group 2 type. Thus Group 2 contrasts with Group I which is normally isolated :Erora crown rot of wheat and grasses. Other fungi isolated in order of frequency were Diplodia maydis, F. rnoniliforme �Subglutinans�, Bipolaris sorokiniana, Nigrospora oryzac, F. roseum �Semitectum�, F. moniliforme, F. roseum �Equiseti�, F. roseum �Concolor�, Macrophomina phaseolina, Rhizoctonia sp., F. roseum �Acuminatum�, F. oxysporum, F. solani, F. tricinctum and F. roseum �Heterosporum�. The relative isolation frequencies of the fungi varied according to the seasonal conditions. Stalk rots were not of major importance in 1973, a relatively dry growing season. However, in 1974, a wet growing season, stalk rot diseases were common in all areas investigated. 2. Isolates of F. roseum �Graminearum�,derived mainly from wheat and maize but also from other sources and from various regions of eastern Australia, were examined for perithecia formation, colony characteristics, fertility, colony growth, conidia production and conidia size. The distribution of the fungus in field colonized maize and wheat plants was also studied. The Group 1 isolates did not produce perithecia, were heterothallic and very infertile, had a mean colony growth of 4.4 cm per 3 days (range, 3.9- 5.1) and produced relatively large numbers of conidia. In contrast, Group 2 isolates were homothallic and produced perithecia readily, had a mean colony growth of 5.4 cm per 3 days (range, 4.7�6.1) and produced relatively low numbers of conidia. Group 1 isolates were found to be commonly associated with crowns and roots of plants and Group 2 isolates were commonly associated with aerial plant parts. 3. The ability of a number of Group 1 and Group 2 isolates to produce the fungal hormone, zearalenone was assessed. Group I isolates produced three to four times more zearalenone than Group 2 isolates. In addition, a. culture which had previously produced perithecia but had lost that ability following numerous transfers, produced no detectable zearalenone. The results provided good evidence that the observed difference in perithecia formation was directly related to the ability to produce zearalenone. 4. The pathogenicity to wheat, maize and carnations of Group 1 isolates from crown rot affected wheat plants and Group 2 isolates from stalk rot affected maize plants was tested. Pathogenicity of 11 other isolates from teosinte, carnations, pearl millet, wheat and barley scab, banana, ginger and common wheat grass was also assessed. The results indicated that pathogenic specialization exists within F. roseum �Graminearum�. Wheat isolates were the most pathogenic to wheat, carnation isolates were the most pathogenic to carnations and all maize isolates were pathogenic to maize while those from wheat and common wheat grass were not as pathogenic to maize. Moreover, Group 2 isolates were more pathogenic when inoculated in aerial plant parts, and the Group I isolates were more pathogenic when inoculated in plant parts in soil. Inoculations on wheat seedlings in sterile field soil demonstrated that the inherent pathogenicity to wheat seedlings of isolates from wheat and maize were similar. 5. Some factors which could contribute to the observed pathogenic differences between isolates from wheat and maize to wheat seedlings in field soil were examined. Conidia volume, germination rate and inherent germinability in the soil were studied. The Group I isolates had the largest volume, the most rapid germination and the highest inherent germinability. Pathogenicity was positively correlated with conidium volume and inherent germinability. In addition, the inherent germinability and conidium volume were positively correlated. Thus, it was established that pathogenic behaviour of conidia of Group 1 and Group 2 reflected differences in conidia morphology.

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No description available.

Sclerotium bataticola Taub., the sclerotial stage of Macrophomina phaseoli (Maubl.) Ashby, was first described as the cause of a sweet potato rot in 1913... Since then, it has received considerable attention as the cause of crown blights or charcoal rot of at least 284 species of plants. [...]

There are many health issues surrounding Alberta’s forests today and for the future. Health impacts of diseases, pests and climate change are currently being predicted in order to implement new management ideas and solutions, and identify specific research needs. This study examines state of the art knowledge on the current impacts of Armillaria root disease (ARD) (Armillaria spp.) in Alberta’s boreal forest region. It also assesses the biology and structure of the disease within this region to predict the extent to which the boreal forest may be impacted. In the next 50 years, both Armillaria ostoyae (Romag.) Herink and Armillaria sinapina Bérubé & Dessureault will become more of a problem, due to climate change and the current mature state of Alberta’s forests. A. sinapina, as a less-pathogenic but more opportunistic species, is predicted to be more prevalent that A. ostoyae, since the former will flourish when there are environmental stresses. Management practices will require research and evaluation of the use of alternative native tree species that have a higher resistance to the Armillaria species within Alberta and the impacts of such alternatives to the forestry industry and community structure. Future research is also essential to determine if one promising biological control agent and fungus, Hypholoma fasciculare (Huds. ex. Fr.), will be a viable and cost effective method to control Armillaria species within Alberta.