Epidemiology in Relation to Methods for Forecasting Light Leaf Spot (Pyrenopeziza brassicae) Severity on Winter Oilseed Rape (Brassica napus) in the UK

Pyrenopeziza brassicae, cause of light leaf spot of oilseed rape, has a complex polycyclic life cycle. It can be difficult to control light leaf spot in winter oilseed rape in the UK since it is not easy to optimise fungicide application timing. Early autumn infections are usually symptomless and recognisable lesions do not develop until the epidemic has progressed further by the spring. Light leaf spot often has a patchy distribution in winter oilseed rape crops and estimation of disease incidence can be difficult. There is evidence that epidemics are initiated primarily by ascospores produced from apothecia that survive the summer inter-crop period on infected debris. Subsequent development of the epidemic during the winter and spring is maintained by rain-splashed conidia that spread light leaf spot from initial foci. Understanding the relative roles of ascospores and conidia in the light leaf spot life cycle is crucial for forecasting epidemic severity and developing control strategies. The current web-based regional forecast system provides an autumn forecast of the incidence of light leaf spot that can be expected the following spring. This is based on survey data which assesses the occurrence of disease the previous July, and weather factors, such as deviations from summer mean temperature and winter rainfall. The forecast can be updated throughout the autumn and winter and includes crop-specific elements so that growers can adjust risks by inputting information about cultivar, sowing date and fungicide use. Crop-specific forecasts can be confirmed by assessing the incidence of light leaf spot. Such assessments will become easier when immunodiagnostic methods for detection of the disease become available. Incorporation of information on spore biology (e.g. apothecial maturation, ascospore release and infection conditions) is considered as a component of the interactive, continuously updated, crop-specific, web-based forecasts which are needed in the future.     

Carbohydrate absorption by chicks affected with the fatty liver and kidney syndrome.

Chicks with fatty liver and kidney syndrome (FLKS) were given oral doses of one of the following test solutions: water, glucose, maltose, starch. Plasma glucose concentration was measured during the four subsequent hours. All FLKS-affected chicks were hypoglycaemic before treatment. Although in some cases plasma glucose concentration increased slightly in the FLSK-chicks given water alone, significantly greater increases were invariably observed following the administration of carbohydrate to sick birds. Results obtained from dietary experiments in which starch was replaced by glucose in a ration causing high mortality from the syndrome revealed no beneficial effect due to the substitution. It was concluded that FLKS does not involve any major impairmant of carbohydrate digestion or absorption.     

Changes in plasma lipid and glucose levels during the onset of fatty liver and kidney syndrome in chics

Plasma glucose, free fatty acid and triglyceride levels were measured during the onset of fatty liver and kidney syndrome in chicks. Intial studies indicated that behavioural and clinical changes characteristically associated with the syndrome were observed only during the 24 h preceding death. A more detailed examination of the blood changes was made on fasted birds. Typically, affected birds could be distinguished from healthy fasted birds by a hypoglycaemia which developed within 2.5 h of the removal of food, and a slightly higher and more sustained elevation of free fatty acid levels. Triglyceride values were not generally different from those found in normal birds. Although moderate to large amounts of lipid were occasionally observed in the kidneys of healthy fasted birds, only in affected birds was significant lipid infiltration of the kidneys associated with a similar level of lipid infiltration of the liver. In extreme cases death from fatty liver and kidney syndrome could occur within 4 h of the removal of food.     

Tasco-Forage: I. Influence of a seaweed extract on antioxidant activity in tall fescue and in ruminants

Seaweed (Ascophyllum nodosum) is a known source of plant growth regulators, and application to turfgrasses has increased activity of the antioxidant superoxide dismutase (SOD) and specific vitamin precursors. Increased antioxidant activity in both plants and animals diminishes oxidative stress. Two pasture experiments investigated effects of Tasco-Forage (a proprietary seaweed-based product) applied to tall fescue (Festuca arundinacea) on antioxidant activity in plants and in ruminants that grazed the forage. In Exp. 1, fescue was 70 to 100% infected with the endophyte fungus Neotyphodium coenophialum ([Morgan-Jones and Gams] Glenn, Bacon, and Hanlin). Twenty-four wether lambs (initial BW 41 kg; SD = 5) grazed fescue treated with 0, 1.7, or 3.4 kg Tasco/ha applied in April and July, 1994, with four replications per treatment. Grazing occurred for 26 d beginning April 21 and for 22 d beginning July 19. In July, there was a linear increase in daily gains (P < 0.05), and serum vitamin A (P < 0.13) and whole-blood Se (P < 0.10) tended to increase in lambs grazing Tasco-treated fescue. In Exp. 2,48 Angus and Angus x Hereford steers (initial BW 245 kg; SD = 20) grazed infected or uninfected tall fescue in Virginia that was treated (3.4 kg/ ha) or untreated with Tasco in April and July, 1995. Steers that grazed infected tall fescue had lower (P < 0.02) serum vitamin A and E and tended (P < 0.07) to have lower whole-blood Se in September compared with steers that grazed uninfected tall fescue. Tasco decreased (P < 0.06) serum vitamin E but tended to increase whole-blood Se (P < 0.10) in September and serum vitamin A in July (P < 0.12). During 1996 and 1997, the experiment was repeated in Virginia with Angus steers and was replicated at Prairie, MS, where 1/4 Brahman x 3/4 Angus steers were used. Forty-eight steers were included at each location in each year (n = 192 total steers for 1996 and 1997). Steers that grazed infected tall fescue in Mississippi had lower (P < 0.05) serum vitamin E by the end of the grazing season. At both locations Tasco increased (P < 0.05) activity of superoxide dismutase in both infected and uninfected fescue. The endophyte in tall fescue seemed to decrease antioxidant activity in grazing steers, whereas Tasco seemed to increase antioxidant activity in both the forage and the grazing ruminant. Tasco may provide opportunities to reduce oxidative stress in plants and animals.