In vitro selection of sterol-biosynthesis-inhibitor (SBI)-resistant mutants in Monilinia fructicola (Wint.) Honey

The inherent resistance risk forMonilinia fructicola against sterol-biosynthesis inhibitors (SBIs) was estimated inin vitro andin vivo laboratory studies. Several mutant strains were selected on media amended with the triazole fungicides penconazole, etaconazole or the morpholine fungicide fenpropimorph.The potential forM. fructicola to develop resistance to the triazoles or to the morpholines was similar.The level of resistance attained did not differ for the two classes of fungicides after a single cycle of treatment with nitrosoguanidine (NTG). Attemps to select mutants with a higher level of resistance to penconazole after successive mutagenic treatments were successful. Most of the mutants were less fit than wild-type strains. Mutants with a low level of resistance had an almost normal mycelial growth rate, whereas growth of mutants with a higher level of resistance was significantly reduced. Spore production was highest in the wild-type strains, similar to the latter in a few resistant strains and less in most others. Only one mutant with an intermediate level of resistance could successfully compete in a mixed population with a wild type strain during successive infection cycles on peaches. Resistance was not stable in highly resistant mutants. Cross resistance to the inhibitors of 14-methylsterol demethylation (DMIs) tested was confirmedin vitro andin vivo for all mutant strains. One DMI-resistant mutant was also resistant to fenpropimorph and two fenpropimorph-resistant mutants were resistant to penconazole.     

Ergosterol biosynthesis inhibitors. An overview of their history and contribution to medicine and agriculture

Over the past 15 years, an increasing number of ergosterol biosynthesis inhibitors (EBIs) have been introduced in crop protection as fungicides, and in medicine as fungicides and bactericides. Their spectrum of activity and their systemic properties vary widely, depending on structural elements. By their high protective and curative activity the EBIs have greatly improved the level of disease control, both in plants and in man. However, the chemical and biological potential of this group has not yet been fully explored, particularly in the field of growth regulation.     

Plasma cholesterol levels and short-term adaptations of metabolism and milk production during feed restriction in early lactating dairy cows on pasture

Low plasma total cholesterol (TC) concentrations are characteristic during the negative energy balance in early lactating dairy cows. The objective was to investigate short-term effects of different TC concentrations during an aggravated energy deficiency through a 1-week concentrate withdrawal on adaptations of metabolism and milk production. Multiparous Holstein cows (n = 15) were investigated during 3 week beginning at 24 ± 7 DIM (mean ± SD). Cows were kept on pasture and received additional concentrate in experimental week 1 and 3, while in week 2, concentrate was withdrawn. Blood was sampled once and milk twice daily. Based on their average TC concentration during week 1 (prior to concentrate withdrawal), cows were retrospectively assigned into a high (H-Chol; n = 8, TC ≥ 3.36 mmol/L) and a low TC groups (L-Chol; n = 7, TC < 3.36 mmol/L). Concentrations of phospholipids and lipoproteins were higher in H-Chol compared to L-Chol throughout the study (p < 0.05). During concentrate withdrawal, milk yield, glucose and insulin concentrations decreased similarly in both groups, while milk fat, milk acetone and plasma BHB were higher in H-Chol compared to L-Chol (p < 0.05). Compared to initial values, plasma NEFA, TAG and VLDL increased in both groups within 2 days after concentrate withdrawal (p < 0.05). Concentrations of NEFA during week 2 were greater in L-Chol compared to H-Chol (p < 0.05). Despite reintroduction of concentrate, milk yield in H-Chol remained lower for two more days compared to week 1 (p < .05), whereas milk yield recovered immediately in L-Chol. Activity of aspartate aminotransferase was higher in H-Chol compared to L-Chol in week 2 (p < 0.05). Greater plasma TC concentrations were associated with a reduced increase of NEFA. Further research is warranted if TC concentrations are related to adipose tissue mobilization and fatty acid turnover.     

Control of soil-borne pathogens with living bacteria and fungi: Status and outlook

This review addresses some of the current problems with soil-borne pathogens and their economic importance in comparison to the total plant protection market- Possible opportunities for biological control solutions in view of the various constraints of western agricultural production are discussed. More specifically, we address the scientific, economic and conceptual hurdles which have slowed down the development of biocontrol agents. In addition, examples of biological control of soil-borne pathogens which have already reached the market or are likely to be exploited commercially within the next few years are presented. Finally, we speculate on certain developments which might become important for the further commercial development of biological control products.     

Physiological and behavioural responses of grazing dairy cows to an acute metabolic challenge

Due to seasonal changes in the quality and quantity of herbage, the nutrient supply to grazing dairy cows is not always sufficient, which may increase their metabolic load. To investigate the temporal pattern of behavioural changes in relation to concomitant metabolic alterations, we subjected 15 multiparous early lactating Holstein dairy cows (24 (SD 7.4) days in milk) to a short‐term metabolic challenge, which we provoked by abruptly withdrawing concentrate for 1 week. Cows grazed full‐time and were supplemented with concentrate in experimental week (EW) 1 and EW 3, whereas concentrate was withdrawn in EW 2. We analysed milk and blood samples to characterise the metabolic changes and found that the total yield of milk and protein decreased (p < 0.05) and fat yield, fat‐to‐protein ratio and acetone content increased (p < 0.05) from EW 1 to EW 2. Plasma glucose and insulin concentrations were lower (p < 0.05), and concentrations of nonesterified fatty acids and beta‐hydroxybutyrate were higher (p < 0.05) in EW 2 compared with EW 1. Apart from ingestive and rumination behaviour and activity, we also monitored the use of an automated brush on pasture. While time spent eating and ruminating increased (p < 0.05) in EW 2 compared with EW 1, time spent idling decreased (p < 0.05). Concomitantly, while time standing and moving increased (p < 0.05) from EW 1 to EW 2, walking time decreased (p < 0.05). The daily proportion of cows using the automated brush decreased (p < 0.05) in EW 2 compared with EW 1, as did the duration of brushing per day. In conclusion, grazing cows experiencing a metabolic challenge try to compensate for the nutrient deficiency by increasing eating time, a behavioural element important for short‐term survival. Due to the strong impact of weather conditions, we cannot currently recommend observation of outdoor brushing activity to address short‐term alterations in the metabolic state of grazing cows.     

The viscosity of mineral oils in relation to their ability to inhibit the transmission of stylet-borne viruses

Thirteen fractions were obtained by distillation of the mineral oil Bayol 50 (ESSO 2214) and these were tested for their ability to inhibit the transmission of potato virus Y to red pepper. The less viscous fractions <8 cSt at 37°C (52 SUS) were shown to be less active, the more viscous fractions were more active than Bayol 50 with a viscosity of 8 cSt at 37°C. Sunoco 7E, a mineral oil with a viscosity of 14.2 cSt at 37°C (74 SUS) was shown to be significantly more active than Bayol 50. The difference in emulgator had no influence on these results. We, therefore, recommed to choose mineral oils with a viscosity of at least 12 cSt at 37°C (=66 SUS) for future work on the inhibition of the transmission of stylet-borne viruses.Samenvatting Door destillatie van de minerale olie Bayol 50 (ESSO 2214) werden 13 fracties verkregen die getoetst werden op hun vermogen de overdracht van aardappelvirus Y naar paprika te verhinderen. De minder viskeuze fracties, <8 cSt bij 37°C (52 SUS), bleken minder, de hoger viskeuze fracties meer activiteit te bezitten dan Bayol 50 zelf. Sunoco 7E, een minerale olie met een viscositeit van 14,2 cSt bij 37°C (74 SUS) bleek significant actiever dan Bayol 50 met een viscositeit van 8 cSt bij 37°C (52 SUS). Een verschil in emulgator had geen invloed op deze resultaten. Op grond van deze gegevens is het aan te bevelen geen minerale olie te gebruiken met een viscositeit lager dan 12 cSt bij 37°C (66 SUS) indien men de overdracht van een nonpersistent virus zo effectief mogelijk wenst te verhinderen.