Voor de practische kweker bruikbare methoden van resistentie-onderzoek

Summary In breeding new varieties it will be necessary in most cases to test the degree of resistance of the material by means of artificial infection. After discussing with plant breeders and phytopathologists the question of the research on disease resistance now being done in the Netherlands the Department of Research on Disease Resistance of the Institute for Phytopathological Research at Wageningen have found that the methods mentioned in addendum I are reliable enough to be used by the breeders themselves, though with the aid of the Department.The methods applied in special institutes because they are too complicated for the breeders, are mentioned in addendum II; they are wart-disease testing in potatoes, virus testing in strawberries and raspberries.Under III are treated the methods that are as yet not sufliciently developed to be applied successfully either by institutes or by breeders, and which are now being investigated in the Netherlands.     

A comparison of the pharmacological activity in cows of two suspensions of betamethasone alcohol

The activity of two betamethasone (BM) suspensions, which differed only in their solids:vehicle ratio, was examined in cattle. Two groups of 10 cows received by subcutaneous injection either 20ml of a 2mg/ml aqueous suspension of BM alcohol or 2ml of a 20mg/ml aqueous suspension. A further 10 cows served as a saline-treated control group.

The mean peak plasma BM concentration was significantly higher in cows treated with 2mg/ml suspension. However, plasma BM levels tended to be maintained for longer by the 20mg/ml suspension. A depression of early morning cortisol levels, similar to that seen with other synthetic glucocorticoids, was recorded with both BM preparations; the depression outlasted the presence of BM. Plasma glucose levels and circulating neutrophil numbers were elevated by BM treatment, and the magnitude and duration of these changes was related to the solids:vehicle ratio of the injected suspensions. The more concentrated suspension was absorbed more slowly and thus produced effects of greater duration.     

Evidence for a new field Culicoides vector of African horse sickness in South Africa

Between February and May 1998, approximately 100 horses died of African horse sickness (AHS) in the cooler, mountainous, central region of South Africa. On 14 affected farms, 156,875 Culicoides of 27 species were captured. C. imicola Kieffer, hitherto considered the only field vector for AHS virus (AHSV), constituted <1% of the total Culicoides captured, and was not found on 29% of the farms. In contrast, 65% of the Culicoides were C. bolitinos Meiswinkel, and was found on all farms. Five isolations of AHSV were made from C. bolitinos, and none from 18 other species of Culicoides (including C. imicola).     

Root growth conditions in the topsoil as affected by tillage intensity

Many studies have reported impeded root growth in topsoil under reduced tillage or direct drilling, but few have quantified the effects on the least limiting water range for root growth. This study explored the effects of tillage intensity on critical soil physical conditions for root growth in the topsoil. Samples were taken from a 7-year tillage experiment on a Danish sandy loam at Foulum, Denmark (56°30′ N, 9°35′ E) in 2008. The main crop was spring barley followed by either dyer's woad (Isatis tinctoria L.) or fodder radish (Raphanus sativus L.) cover crops as subtreatment. The tillage treatments were direct drilling (D), harrowing 8-10 cm (H), and ploughing (P) to 20 cm depth. A chisel coulter drill was used in the H and D treatments and a traditional seed drill in the P treatment. Undisturbed soil cores were collected in November 2008 at soil field moisture capacity from the 4-8 and 12-16 cm depths.We estimated the critical aeration limit from either 10% air-filled porosity (ε_a) or relative gas diffusivity (D/D₀) of 0.005 or 0.02 and found a difference between the two methods. The critical limit of soil aeration was best assessed by measuring gas diffusivity directly. Root growth was limited by a high penetration resistance in the D and H soils (below tillage depth). Poor soil aeration did not appear to be a significant limiting factor for root growth for this sandy loam soil, irrespective of tillage treatment. The soil had a high macroporosity and D/D₀ exceeded 0.02 at field capacity. Fodder radish resulted in more macropores, higher gas diffusivity and lower pore tortuosity compared to dyer's woad. This was especially important for the H treatment where compaction was a significant problem at the lower depths of the arable layer (10-20 cm depth). Our results suggest that fodder radish could be a promising tool in the amelioration of soil compaction.     

A novel fish counter for fish farms

A counter for rapid counting of live fish, especially trout and salmon, has been developed. The response time of the counter is approximately 100 ms and hence a throughput of up to 10 000 fish per hour can be obtained. Results are given in the paper for counting fish of between 300 g and 1 kg with an error of less than ± 3%.     

Live chilling of Atlantic salmon: physiological response to handling and temperature decrease on welfare

Investigation of the physiological effects of live chilling in Atlantic salmon, Salmo salar, has been performed in two experiments. In the first, fish (mean weight 840 g) acclimatized to either 16, 8, or 4°C were directly transferred horizontally or vertically (9 combinations) to water temperatures of 16, 8, 4, or 0°C using a dip net. Blood samples were collected at 1 and 6 h (h) post-transfer. In the second experiment, fish (mean weight 916 g) acclimatized to 16°C were exposed to four temperature-drop regimes (no physical handling): 16–4°C (over 5 h), 16–4°C (over 1 h), 16–0°C (over 5 h), and 16–0°C (over 1 h). Blood samples were collected 1 h post-temperature drop. Physical transfers in the first trial, i.e., temperature drops, resulted in immediate (1 h) increases in blood lactate concentrations at all three temperatures, but levels were significantly reduced and close to pre-transfer levels after 6 h. Horizontal transfers, i.e., 16–16°C, 8–8°C, and 4–4°C, resulted in similar increases and were not significantly different from the groups exposed to temperature drops. The most severe vertical transfer (16-0) resulted in a swift loss of equilibrium and eventually death. In experiment 2, temperature drops from 16 to 4°C and from 16 to 0°C over a period of one or 5 h, without physically handling the fish, resulted in no significant increases in any of the measured parameters 1 h post-transfer, except in the 16–0 (1 h) group. The latter experienced a significant increase in blood sodium, glucose, lactate, and cortisol levels compared to all other groups. The results suggest that salmon are capable of tolerating relatively steep temperature drops without any significant negative effects on blood stress parameters and that physical stress from handling overrides the effect of thermal insults.