Elisa Gauslå

Overingeniør

(+47) 920 43 914
elisa.gauslaa@nibio.no

Sted
Ås - Bygg H7

Besøksadresse
Høgskoleveien 7, 1433 Ås

Sammendrag

The plant pathogenic fungus Fusarium langsethiae produces the highly potent mycotoxins HT-2 and T-2. Since these toxins are frequently detected at high levels in oat grain lots, they pose a considerable risk for food and feed safety in Norway, as well as in other north European countries. To reduce the risk of HT-2/T- 2-contaminated grain lots to enter the food and feed chain, it is important to identify factors that influence F. langsethiae infection and mycotoxin development in oats. However, the epidemiology of F. langsethiae is unclear. A three-year survey was performed to reveal more of the life cycle of F. langsethiae and its interactions with oats, other Fusarium species, as well as insects, mites and weeds. We searched for inoculum sources by quantifying the amount of F. langsethiae DNA in crop residues, weeds, and soil sampled from a selection of oat-fields. To be able to define the onset of infection, we analysed the amount of F. langsethiae DNA in oat plant material sampled at selected growth stages (between booting and maturation), as well as the amount of F. langsethiae DNA and HT-2 and T-2 toxins in the mature grain. We also studied the presence of possible insect- and mite vectors sampled at the selected growth stages using Berlese funnel traps. The different types of materials were also analysed for the presence F. graminearum DNA, the most important deoxynivalenol producer observed in Norwegian cereals, and which presence has shown a striking lack of correlation with the presence of F. langsethiae in oat. Results show that F. langsethiae DNA may occur in the oat plant already before heading and flowering. Some F. langsethiae DNA was observed in crop residues and weeds, though at relatively low levels. No Fusarium DNA was detected in soil samples. Of the arthropods that were associated with the collected oat plants, aphids and thrips species were dominating. Further details will be given at the meeting.

Sammendrag

Downy mildew, caused by Hyaloperonospora parasitica s.l., represents an increasing threat to Norwegian production of cruciferous vegetable crops. Although the pathogen has been present in Norway for over a century, the intensified production regimes of field vegetables has contributed to an increase in disease incidence and severity. The project “Effective and sustainable control strategies for downy mildew in rocket, broccoli and cauliflower” were initiated by vegetable growers and financed by the Norwegian Research Council, “Jordbruksavtalen”, “Fondet” and vegetable growers for the period 2009-2011. As part of the project we have surveyed the presence of downy mildew in cruciferous crops and weeds, tested possible cross inoculation between different cruciferous crops and weeds, and tested how long detached spores can survive in air.   The survey of downy mildew incidence in cruciferous crops (mainly rocket, broccoli and cauliflower) and weeds were performed by local extension officers in the Counties Buskerud, Rogaland, Vestfold, østfold, and Hedmark. In addition, 65 growers were asked to survey and report findings in their fields. During the project period downy mildew incidence was mainly observed in wild rocket (Diplotaxis tenuifolia) and broccoli, while a few incidences of downy mildew were reported in swede, oil seed rape and the weed Sheperd’s purse (Capsella bursa-pastoris). The host range of isolates collected in the survey was assessed on a selection of cruciferous species.  Seedlings of wild rocket (‘DI902’), cultivated rocket (Eruca sativa), cauliflower (‘Freedom’), broccoli (‘Ironman’), oil seed rape (‘Valo’) and swede (‘Vige’) were inoculated by spraying the cotyledons with a spore suspension. One week after inoculation, the seedlings were incubated over-night at high RH and scored for positive infections by observation of visible sporulation on the cotyledons. Preliminary results show that downy mildew from oil seed rape can infect swede, cauliflower and broccoli. Isolates from broccoli were partly virulent on cauliflower. An isolate from swede were virulent on broccoli, while an isolate from rape were virulent on cauliflower, broccoli and swede. An isolate from Sheperd’s purse was virulent on broccoli. Isolates from wild rocket were not virulent on any of the other plants in the trial. The results indicate a risk of cross infection between different cruciferous species, although also supporting the ongoing discussions on dividing H. parasitica into separate species. The possibility of long distance dispersal of viable spores depends on how long the spores can survive in free air. Spores from freshly sporulating rocket seedlings were transferred to filter paper and exposed to solar radiation or in shade. Preliminary results show that spores were not able to germinate after 6 hours exposure to the sun, while shaded spores were able to survive for 24 hours or more. These results will be included in the development of a forecasting model for downy mildew on cruciferous crops.  

Sammendrag

Carrot roots with cavity spot lesions from 8 different counties in Norway were sampled and Pythium species were isolated on selective medium. Pythium spp. were characterised morphologically and by species-specific PCR. Laboratory experiments with inoculations of carrot roots were performed. A total of 130 isolates out of 230 Pythium-like isolates tested with PCR were identified as pathogenic species of Pythium. These were P. intermedium (29 %), P. sulcatum (23 %), P. sylvaticum (16 %), P. violae (15 %) and a possible new Pythium species designated P. "vipa" (18 %). There were some difference between geographical regions and ages of cavities regarding the frequency of the different species isolated. When rating sunken lesions in the laboratory inoculation experiments, P. "vipa" was the most aggressive and P. violae the least aggressive species. P. intermedium and P. "vipa" caused more discolouration of the infected carrot tissue than the other species. The importance of the different Pythium spp. as agents of cavity spot in Norway is discussed.