Understanding the Interactions between Phoma Stem Canker (Leptosphaeria maculans and L. biglobosa) and Light Leaf Spot (Pyrenopeziza brassicae) Pathogens of Oilseed Rape (Brassica napus)

The aim of this project was to understand the interspecific interactions between Leptosphaeria maculans, L. biglobosa and Pyrenopeziza brassicae in oilseed rape through identification of interactions at different levels of investigation. The aim was achieved by (1) investigating the interactions between phoma stem canker (L. maculans and L. biglobosa) and light leaf spot (P. brassicae) causal pathogens in vitro and in planta; (2) examining the interactions between L. maculans and P. brassicae on different cultivars under field conditions; (3) identifying relationships between weather, prevalence of light leaf spot or phoma leaf spot and stem canker and yield loss. Results of this project show that both direct and indirect interspecific interactions exist between L. maculans, L. biglobosa and P. brassicae. The results of in vitro experiments showed that L. maculans produces a phytotoxin called sirodesmin PL when cultured on its own, whereas when L. biglobosa or P. brassicae were cultured on their own sirodesmin PL was not produced. When secondary metabolite extracts from liquid culture filtrates from these three pathogens cultured on their own were applied to fungal plugs of L. maculans, L. biglobosa or P. brassicae, the only extract that reduced colony area was the secondary metabolite extract from L. maculans applied to L. biglobosa and P. brassicae. However, when the culture filtrate from L. maculans and L. biglobosa simultaneously cultured together was applied, there was no reduction in colony area of L. biglobosa or P. brassicae, nor was sirodesmin PL identified in the secondary metabolite extracts. Interestingly, when L. maculans and L. biglobosa were sequentially cultured 7 days apart, the secondary metabolite extract decreased the colony area of both L. biglobosa and P. brassicae, and contained sirodesmin PL. This implies that Sirodesmin PL had an inhibitory effect on L. biglobosa and P. brassicae. Therefore, these experiments showed that direct interspecific interactions exist between these three pathogens, and that direct interactions when Leptosphaeria spp. are simultaneously co-inoculated indirectly influence P. brassicae due to inhibition of Sirodesmin PL production that would not inhibit P. brassicae growth. A similar pattern was observed in planta when oilseed rape cotyledons were inoculated with L. maculans, L. biglobosa or a mixture of both Leptosphaeria spp. Large, undefined lesions developed when L. maculans conidia were applied and smaller, more well-defined dark lesions developed when L. biglobosa conidia were applied. However, when a mixture of both Leptosphaeria spp. were applied, the phenotype of the lesion was more similar to that of L. biglobosa rather than L. maculans, suggesting that L. biglobosa outcompeted L. maculans in a simultaneous infection situation. When secondary metabolite extractions were analysed, sirodesmin PL was found only in the L. maculans only treatment, not in the L. biglobosa or the Leptosphaeria spp. mixture treatments. These findings show that the interspecific interactions found in vitro were also found in planta. Additionally, in planta work using near-isogenic oilseed rape lines with or without the Rlm7 gene provided preliminary data to suggest that the presence of Rlm7 may increase the susceptibility of plants to L. biglobosa. The field experiments showed that cultivar resistance and fungicides were effective at reducing phoma stem cankers and P. brassicae sporulation as well as reducing the transmission of Leptosphaeria spp. inoculum between seasons. The monitoring of ascospore release events showed that there were differences in release timing and relative quantities of inoculum between seasons, including the simultaneous release of Leptosphaeria spp. ascospores with P. brassicae ascospores. Additionally, due to the long asymptomatic latent period between P. brassicae infection and presence of indicative light leaf spot disease symptoms, such as P. brassicae sporulation, there is no defined threshold for fungicide application to control P. brassicae. So, autumn disease control for phoma stem canker and light leaf spot causal pathogens is often defined by when the L. maculans fungicide threshold is met, irrespective of L. biglobosa or P. brassicae ascospore release events. In England and Wales, analysis of relationships between weather and light leaf spot disease prevalence or yield loss found the prevalence of P. brassicae pod lesions had positive relationships with autumn or winter temperature and a negative relationship with the number of autumn or winter air frosts. This suggests that warmer temperatures and fewer air frosts would result in a greater prevalence of P. brassicae pod lesions. There was also a positive correlation between average precipitation or mean number of rain-days in winter and spring and incidence of light leaf spot pod lesions. Met Office weather data has shown that the 5-year mean temperature average since 1969 for autumn and winter has increased whereas spring precipitation has not changed. Therefore, if this trend continues with autumn and winter getting warmer, this will increase the probability of P. brassicae infection. Therefore, findings from all experiments in this study suggest that; • Changes in Leptosphaeria spp. ascospore release patterns under natural conditions influence direct interspecific interactions between L. maculans and L. biglobosa, which indirectly affect P. brassicae. • The widespread adoption of effective integrated L. maculans control strategies under P. brassicae favourable weather conditions may unintentionally make the UK oilseed rape crops more vulnerable to P. brassicae infection. • Development of integrated pest management strategies is required to improve the control of L. maculans, L. biglobosa and P. brassicae together rather than in isolation

Survival of acid-adapted Salmonella typhimurium in fermented millet and acidified broth at different storage temperatures

Salmonella typhimurium KSN 533 was adapted to acid by exposure to lactic acid at pH 5.0 for 18 h. Subsequently, acid-adapted and non-adapted cells were challenged with lactic acid (pH 3.8) in Brain-heart infusion (BHI) at 4°C and 30°C. Acid-adapted and non-adapted cells were also inoculated into already fermented millet broth (pH 3.8) and at beginning of millet fermentation with Lactobacillus fermentum starter culture. Survival curves of acid-adapted and non-adapted cells at pH 3.8 were fitted with the Weibull distribution model. Acid-adapted cells were generally resistant to subsequent acid stress than non-adapted cells. Regardless of adaptation, cells were more sensitive to acid shock (pH 3.8) at 30°C than at 4°C storage. Whereas both acid-adapted and non-adapted S. typhimurium cells survived in appreciable numbers of 5.5 and 3.5 log cfu/ml respectively after 72 h storage at 4°C, no viable cells were detected for both acid-adapted and non-adapted cells after 12 an 9 h respectively at 30°C. Acid-adaptation induced protection against lethal acid and cross protection against cold stresses. Regardless of adaptation, viable population of Salmonella showed a slight increase during the early stages of millet fermentation. Similar inactivation rates were observed for both acid-adapted and non-adapted cells when inoculated at the beginning of fermentation. Thus acid adaptation does not appear to influence survival of S. typhimurium when inoculated at the beginning of the fermentation although acid-adapted cells survived better in already fermented millet. Keywords: acid-adaptation, millet fermentation, Salmonella, lethal acid challeng

Estimation of the economic relationship of an airport to the regional economy : a critical analysis

September 1981Includes bibliographical references (leaves 122-124)In the past decade many major U.S. airports have encountered extensive opposition to plans for future growth and expansion from environmentalists and community groups who cite the noise and air pollution created and the use of increasingly scarce land resources. In an effort to counterbalance these criticisms and highlight the regional benefits the airport provides, several airport authorities have completed economic impact studies which attempt to define the airport's role in the regional economy. In reviewing the airport economic impact studies which have been completed in the past twenty years, it is obvious that a wide range of methodologies have been developed to accomplish the common task of estimating the different elements of airport economic impact. This thesis provides an overview and critical evaluation of the techniques used in past studies to define what is the airport economic impact and how is the impact estimated in the absence of primary data. Three major economic impact categories, primary, direct and induced, provide the framework for analysis. An economic impact case study of Boston's Logan International Airport is presented to provide insight into problems common to all airport economic impact studies and the solutions to these problems in a specific situation. The need for and direction of future research to clarify and define the quantification of the airport/community economic relationships is also recognized and discussed

Effect of early sowing on the growth, yield and quality of sugar beet.

End of Project ReportExperiments have shown that yield of sugar is closely related to the amount of solar radiation intercepted by a sugar beet crop. Early sowing increases leaf area from May onwards when radiation is at its maximum and provides a basis for increasing yields. In the past, bolting has been an undesirable consequence of early sowing but some modern cultivars have good bolting resistance and can be sown early with a limited risk of bolting. This study, conducted from 1994 to 1998, compared the performance of two cultivars, Celt and Monofeb, at three sowing dates and three harvest dates. In replicated experiments, plant establishment, crop development, and root yield and quality were assessed. The effect of sowing date on solar radiation interception was studied. Effects of in-furrow pesticide application on pest numbers and plant damage were also measured. Plant establishment was influenced by sowing date with the early sowings generally giving lower plant numbers than the later ones. The cultivar Celt produced higher populations than Monofeb at all sowing dates. Early sowing increased the leaf area index (a measure of the ratio of leaf to land area) and consequently the amount of solar radiation intercepted. This was particularly so in June when solar radiation levels are highest. Early crop establishment provides the opportunity to exploit good weather conditions which may occur in April or May. Pest numbers generally were small at all the sites. Insecticide had a greater effect on pest numbers and plant damage than it had on plant establishment; the beneficial effects of pesticide were slightly more pronounced for the early and mid-season sowings than for later-sown beet. Seedling diseases were not a problem at any time of sowing. Poor emergence, where it occurred, was not associated with pre-emergence disease. Early to mid-March sowings produced significantly higher yields of roots and sugar than the early or late April sowings over the period of the experiment. Even in years when plant populations from the first sowings were much lower than subsequent sowings, yields tended to be at least equal to those of later sowings. Monofeb produced a slightly higher root yield than Celt, but because it had lower sugar contents there was no difference in sugar yields. Harvesting extended over the period from early October to mid-November and root growth and sugar production increased over that period irrespective of sowing date. Bolting was a problem in 1996 on the early-sown plots, particularly with the cultivar Celt.Teagasc acknowledges the support of Irish Sugar plc and Sugar Beet Levy Farmer Funds in the financing of this projec

Prevalence and characteristics of <em>Listeria monocytogenes</em> isolates in raw milk, heated milk and Nunu, a spontaneously fermented milk beverage in Ghana

Listeria monocytogenes is a gram-positive food-borne pathogen that causes listeriosis in humans. Currently, there is little information on the prevalence of Listeria monocytogenes in raw milk and traditional yoghurt-like milk beverage, nunu, in Ghana. The purpose of this study was to investigate the prevalence of L. monocytogenes isolates in raw cow milk, boiled milk and nunu in Ghana, and to characterize these L. monocytogenes isolates according to their serogroups, virulence potentials and antibiotic susceptibility profiles. A total of 254 samples comprising 114 raw cow milk, 56 boiled milk and 84 nunu were collected from dairy farms and market vendors for detection of L. monocytogenes. The overall prevalence of L. monocytogenes in raw milk, boiled milk and nunu was 5.5% (14/254). Listeria monocytogenes was prevalent in raw cow milk (8.8%; 10/114) and nunu (13.1%; 11/84), while no Listeria spp. was not detected in boiled milk. A total of 62 L. monocytogenes isolates were analysed to belong to molecular serogroups 1/2a-3a (32/62, 51.6%), 1/2b-3b-7 (14/62, 22.6%), 4b-4d-4e (9/62, 14.5%) and 1/2c-3c (7/62, 11.3%). All 62 L. monocytogenes isolates harbored the virulence-associated genes inlA, inlB, inlC, inlJ, plcA, actA, hlyA, iap and prfA. All Listeria monocytogenes in the present study were generally susceptible to the tested antibiotics, except neomycin and tetracycline, for which phenotypic resistance was observed among isolates

Microbial Safety of Milk Production and Fermented Dairy Products in Africa

In Africa, milk production, processing and consumption are integral part of traditional food supply, with dairy products being a staple component of recommended healthy diets. This review provides an overview of the microbial safety characteristics of milk production and fermented dairy products in Africa. The object is to highlight the main microbial food safety hazards in the dairy chain and to propose appropriate preventive and control measures. Pathogens of public health concern including Mycobacterium bovis, Brucella abortus and Coxiella burnettii, which have largely been eradicated in many developed nations, still persist in the dairy chain in Africa. Factors such as the natural antimicrobial systems in milk and traditional processing technologies, including fermentation, heating and use of antimicrobial additives, that can potentially contribute to microbial safety of milk and dairy products in Africa will be discussed. Practical approaches to controlling safety hazards in the dairy chain in Africa have been proposed. Governmental regulatory bodies need to set the necessary national and regional safety standards, perform inspections and put measures in place to ensure that the standards are met, including strong enforcement programs within smallholder dairy chains. Dairy chain actors would require upgraded knowledge and training in preventive approaches such as good agricultural practices (GAP), hazard analysis and critical control points (HACCP) design and implementation and good hygienic practices (GHPs). Food safety education programs should be incorporated into school curricula, beginning at the basic school levels, to improve food safety cognition among students and promote life-long safe food handling behaviour

Technological properties and probiotic potential of <i>Lactobacillus fermentum</i> strains isolated from West African fermented millet dough

BACKGROUND: Throughout Africa, food fermentations are still driven by indigenous microorganisms which influence the nutritional, organoleptic and safety of the final products. However, for improved safety, consistent quality and beneficial health effects, a trend has emerged which involves the isolation of indigenous strains from traditional fermented products to be used as functional starter cultures. These functional starter cultures possess inherent functional characteristics and can contribute to food quality and safety by offering one or more organoleptic, nutritional, technological or health advantage (probiotics). With the aim of selecting potential probiotic starter cultures, Lactobacillus fermentum strains isolated from fermented millet dough were investigated for technological properties and probiotic traits in-vitro. RESULTS: A total of 176 L. fermentum strains were assessed for technological properties including rate of acidification, exopolysaccharide production and amylase activity. Following this, 48 strains showing desirable technological properties were first screened for acid resistance. Sixteen acid resistant strains were assessed for additional probiotic properties including resistance to bile salts, bile salt hydrolysis, antimicrobial property, haemolysis and antibiotics resistance. L. fermentum strains clustered into 3 groups represented by 36 %, 47 % and 17 % as fast, medium and slow acidifiers respectively. About 8 %, 78 % and 14 % of the strains showed strong, weak and no exopolysaccharides production respectively. Amylase activity was generally weak or not detected. After exposure of 48 L. fermentum strains to pH 2.5 for 4 h, 16 strains were considered to be acid resistant. All 16 strains were resistant to bile salt. Four strains demonstrated bile salt hydrolysis. Antimicrobial activity was observed towards Listeria monocytogenes and Staphylococcus aureus but not E. coli and Salmonella enteritidis. Lactobacillus fermentum strains were generally susceptible to antibiotics except 6 strains which showed resistance towards streptomycin, gentamicin and kanamycin. CONCLUSION: In vitro determination of technological and probiotic properties have shown strain specific difference among L. fermentum strains isolated from fermented millet dough. Sixteen (16) L. fermentum strains have been shown to possess desirable technological and probiotic characteristics in vitro. These strains are therefore good candidates for further studies to elucidate their full potential and possible application as novel probiotic starter cultures

Patterns and predictors of antimicrobial resistance among Staphylococcus spp. from canine clinical cases presented at a veterinary academic hospital in South Africa

Background Antimicrobial resistance in staphylococci, often associated with treatment failure, is increasingly reported in veterinary medicine. The aim of this study was to investigate patterns and predictors of antimicrobial resistance among Staphylococcus spp. isolates from canine samples submitted to the bacteriology laboratory at the University of Pretoria academic veterinary hospital between 2007 and 2012. Retrospective data of 334 Staphylococcus isolates were used to calculate the proportion of samples resistant to 15 antimicrobial agents. The Cochran-Armitage trend test was used to investigate temporal trends and logistic regression models were used to investigate predictors of antimicrobial resistance in Staphylococcus aureus and Staphylococcus pseudintermedius. Results Results show that 98.2% (55/56) of the S. aureus isolates were resistant to at least one drug while 42.9% were multidrug resistant. Seventy-seven percent (214/278) of the S. pseudintermedius isolates were resistant to at least one drug and 25.9% (72/278) were multidrug resistant. Resistance to lincospectin was more common among S. aureus(64.3%) than S. pseudintermedius (38.9%). Similarly, resistance to clindamycin was higher in S. aureus (51.8%) than S. pseudintermedius (31.7%) isolates. There was a significant (p = 0.005) increase in S. aureus resistance to enrofloxacin over the study period. Similarly, S. pseudintermedius exhibited significant increasing temporal trend in resistance to trimethoprim-sulphamethoxazole (p = 0.004), clindamycin (p = 0.022) and orbifloxacin (p = 0.042). However, there was a significant decreasing temporal trend in the proportion of isolates resistant to doxycycline (p = 0.041), tylosin (p = 0.008), kanamycin (p = 0.017) and amoxicillin/clavulanic acid (p = 0.032). Conclusions High levels of multidrug resistance and the increasing levels of resistance to sulphonamides, lincosamides and fluoroquinolones among Staphylococcus spp. isolates in this study are concerning. Future studies will need to investigate local drivers of antimicrobial resistance to better guide control efforts to address the problem

Chemical warfare: the fungal quest to conquer oilseed rape

Final Accepted Versio

Prevalence, virulence factor genes and antibiotic resistance of<em> Bacillus cereus sensu lato </em>isolated from dairy farms and traditional dairy products

BACKGROUND: B. cereus are of particular interest in food safety and public health because of their capacity to cause food spoilage and disease through the production of various toxins. The aim of this study was to determine the prevalence, virulence factor genes and antibiotic resistance profile of B. cereus sensu lato isolated from cattle grazing soils and dairy products in Ghana. A total of 114 samples made up of 25 soil collected from cattle grazing farm land, 30 raw milk, 28 nunu (yoghurt-like product) and 31 woagashie (West African soft cheese). Ninety-six B. cereus sensu lato isolates from 54 positive samples were screened by PCR for the presence of 8 enterotoxigenic genes (hblA, hblC, hblD, nheA, nheB, nheC, cytK and entFM), and one emetic gene (ces). Phenotypic resistance to 15 antibiotics were also determined for 96 B. cereus sensu lato isolates. RESULTS: About 72% (18 of 25 soil), 47% (14 of 30 raw milk), 35% (10 of 28 nunu) and 39% (12 of 31 woagashi) were positive for B. cereus sensu lato with mean counts (log(10) cfu/g) of 4.2 ± 1.8, 3.3 ± 2.0, 1.8 ± 1.4 and 2.6 ± 1.8 respectively. The distribution of enterotoxigenic genes revealed that 13% (12/96 isolates) harboured all three gene encoding for haemolytic enterotoxin HBL complex genes (hblA, hblC and hblD), 25% (24/96 isolates) possessed no HBL gene, whereas 63% (60/96 isolates) possessed at least one of the three HBL genes. All three genes encoding for non-haemolytic enterotoxin (nheA, nheB and nheC) were detected in 60% (57/96) isolates, 14% (13/96) harboured only one gene, 19% (18/96) whereas 8% possessed none of the NHE genes. The detection rates of cytk, entFM, and ces genes were 75, 67 and 9% respectively. Bacillus cereus s. l. isolates were generally resistant to β-lactam antibiotics such as ampicillin (98%), oxacillin (92%), penicillin (100%), amoxicillin (100%), and cefepime (100%) but susceptible to other antibiotics tested. CONCLUSIONS: Bacillus cereus s. l. is prevalent in soil, raw milk and dairy products in Ghana. However, loads are at levels considered to be safe for consumption. Various enterotoxin genes associated with virulence of B. cereus are widespread among the isolates