Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
2009
Authors
Belachew Asalf Tadesse Arne Stensvand David M. Gadoury Robert C Seem Andrew Dobson Anne-Marte TronsmoAbstract
Development of ontogenic resistance to powdery mildew (Podosphaera aphanis) in strawberry fruit has not been quantified, and thus cannot be exploited in disease management programs. Four commercially-relevant strawberry cultivars were evaluated for ontogenic resistance to powdery mildew. Fruits were inoculated at one of the four growth stages: flowering, green, white and early pink fruit. There was a significant difference between and within cultivars at the bloom and green stage of inoculations (P <0.05) for both disease incidence and severity. On average 16.4, 39.5, 48.7, and 60.3 % of the fruits inoculated at bloom developed powdery mildew in cultivars Elan, Korona, Frida and Inga, respectively. None of the cultivars developed powdery mildew when inoculated at the pink stage. It may be concluded that flowers and green fruits of strawberry were much more susceptible to powdery mildew infection than white and pink fruits. The high susceptibility of cultivars at the flower and early green stages seemed coincident with the succulent nature of the fruits at these stages, making it easy for penetration and establishment of mildew. Control measures targeting at these critical windows of fruit susceptibility are likely to reduce yield loss.
Authors
Belachew Asalf Tadesse Arne Stensvand David M. Gadoury Robert C Seem Andrew Dobson Anne-Marte TronsmoAbstract
No abstract has been registered
Abstract
European ash (Fraxinus excelsior), also known as common ash, occurs naturally inland in lower areas of southeastern Norway and along the southern coast of the country. It is important both as a forest and ornamental tree. During the last decade, dieback has become a disastrous disease on F. excelsior in many European countries. The anamorphic fungus Chalara fraxinea T. Kowalski (1), described for the first time from dying ash trees in Poland, is now considered the cause of ash dieback (2). In May of 2008, C. fraxinea was isolated from 1.5 m high diseased F. excelsior in a nursery in Østfold County in southeastern Norway. Symptoms included wilting, necrotic lesions around leaf scars and side branches, and discoloration of the wood. From symptomatic branches, small pieces (approximately 1 cm3) were excised in the transition area between healthy and discolored wood. After surface sterilization (10 s in 70% ethanol + 90 s in NaOCl), the pieces were air dried for 1 min in a safety cabinet, cut into smaller pieces, and placed on media. The fungus was isolated on potato dextrose agar (PDA) and water agar (WA). On PDA, the cultures were tomentose, light orange, and grew slowly (21 mm mean colony diameter after 2 weeks at room temperature). Typical morphological features of C. fraxinea developed in culture. Brownish phialides (14.8 to 30.0 [19.5] × 2.5 to 5.0 [4.1] μm, n = 50) first appeared in the center of the colonies on the agar plugs that had been transferred. The agar plugs were 21 days old when phialides were observed. Abundant sporulation occurred 3 days later. Conidia (phialospores) extruded apically from the phialides and formed droplets. Conidia measured 2.1 to 4.0 (3.0) × 1.4 to 1.9 (1.7) μm (n = 50). The first-formed conidia from each phialide were different in size and shape from the rest by being longer (6 μm, n = 10) and more narrow in the end that first appeared at the opening of the phialide. Internal transcribed spacer sequencing confirmed that the morphological identification was correct (Accession No. EU848544 in GenBank). A pathogenicity test was carried out in June of 2008 by carefully removing one leaf per plant on 10 to 25 cm high F. excelsior trees (18 trees) and placing agar plugs from a 31-day-old C. fraxinea culture (isolate number 10636) on the leaf scars and covering with Parafilm. After 46 days, isolations were carried out as described above from discolored wood that had developed underneath necrotic lesions in the bark and subsequently caused wilting of leaves. All the inoculated plants showed symptoms, and C. fraxinea was successfully reisolated. No symptoms were seen on uninoculated control plants (eight trees) that had received the same treatment except that sterile PDA agar plugs had been used.
Abstract
No abstract has been registered
Authors
Ingerd Skow Hofgaard Katarzyna Marzec Guro Brodal Birgitte Henriksen May Bente Brurberg Anne-Marte TronsmoAbstract
Microdochium nivale (syn. Microdochium nivale var. nivale) and Microdochium majus (syn. Microdochium nivale var. majus) are important pathogens which cause snow mould on grasses and winter cereals. These fungi are also able to cause leaf blotch of oat and seedling blight, foot rot and ear blight in cereals. Although no distinct differences in the host range of M. nivale and M. majus are found, indications for differences in host preferences between these fungal species have previously been discussed. The culture collection at Bioforsk contains about 250 Microdochium sp. isolated from grasses and cereals over the last 20 years. Most of the isolates collected from leaves of cereals displaying snow mould symptoms in spring, were identified as M. nivale (71 %), whereas most of the isolates collected from cereal seeds (mostly wheat) belong to the species M. majus (92 %). All, except one out of the sixty nine Microdochium sp. isolated from grass leaves were identified as M. nivale (99 %). The relatively higher incidence of M. majus vs. M. nivale on cereal seeds (mostly wheat) harvested in Norway, is in agreement with studies in UK (Parry et al. 1995). Parry et al. suggested that higher natural occurrence of M. majus (vs. M. nivale) on seeds of cereals could be partly due to the higher proportion of M. majus isolates producing perithecia and thus, a relatively higher amount of M. majus spores spreading to the ear (Parry et al. 1995). The high frequency of M. nivale (99 %) vs. M. majus on grasses collected in Norway could indicate that M. nivale is more aggressive on certain grass species. Studies in our lab indeed point towards a higher aggressiveness of M. nivale vs. M. majus on perennial ryegrass at low temperature (2?C) (Hofgaard et al 2006). However, the high incidence of M. nivale on grass leaves could also be caused by differences in temperature preferences, saprophytic ability or ability to infect certain plant parts. Isolates of M. nivale display a higher in vitro growth rate compared to isolates of M. majus at 2?C (Hofgaard et al. 2006). In conclusion, the higher natural occurrence of M. nivale vs. M. majus on turf grasses and the relatively higher aggressiveness of M. nivale on perennial ryegrass could indicate that M. nivale somehow is better adapted to infect certain grass species.
Abstract
The vine weevil, Othiorynchus sulcatus, is a serious pest in strawberries and biological control methods are needed to combat this pest. Formulations of the insect pathogenic fungus Metarhizium anisopliae is registered for use against Otiorhynchus spp. in several countries but no fungal control agents are avilable for control of O. sulcatus in Norway. All developmental stages of Otiorhynchus spp. are susceptible to virulent insect pathogenic fungal species, but best control has been achieved against the larvae (Moorhouse et al. 1992). A number of studies have shown that M. anisopliae and Beauveria bassiana have good potential against Otiorhynchus spp. (Cross et al. 2001). In field grown strawberries, good control with Metarhizium has been reported when environmental conditions for the fungus are favourable (Oakley 1994). Temperatures in excess of 15oC are required for good control by most fungal isolates. Low temperature is therefore a major restricting factor for use of fungi outdoors (Gillespie et al. 1989, Soares et al. 1983). Isolates with low temperature optimums could therefore be well suited for field conditions in Northern Europe, where soil temperatures at the time when most larvae are found in the soil in autumn are 10-12oC. Norwegian M. anisopliae and B. bassiana isolates have shown promising results against O. sulcatus larvae at low temperatures in laboratory bioassays (Hjeljord & Klingen 2005). One of the Norwegian M. anisopliae isolates has also shown good competition with other soil fungi in laboratory experiments (Hjeljord & Meadow 2005). In addition to being cold tolerant, rhizosphere competence is important for fungal control agents that are used to control root feeding pests. "Rhizosphere competence" has been defined when considering biological control agents as "the ability of a microorganism, applied by seed treatment, to colonize the rhizosphere of developing roots" (Baker 1991). In this study we therefore aimed at testing the survival and rhizosphere competence of two different cold active Norwegian isolates (M. anisopliae isolate NCRI 250/02 and B. bassiana NCRI 12/96) in a semi field experiment in Norway. These were compared with the commercially avilable M. anisopliae isolate Ma43 originating from Austria (the isolate is also known to have many other names (Eilenberg 2008)). The study was conducted by estimating fungal concentrations in the bulk and rhizosphere soil surrounding the strawberry plant roots by counting colony forming unists (CFUs). The highest numbers of B. bassiana NCRI 12/96 CFUs were seen in the rhizosphere at 1.87x109 per liter soil 3 months after application. The highest numbers of M. anisopliae NCRI 250/02 CFUs were seen in the rhizosphere at 2.41x109 per liter soil 1 year after application. Numbers of CFUs for the M. ansiopliae Ma43 CFUs were generally lower than for the Norwegian isolates, but also for this isolate a higher fungal concentration was found in the rihzosphere soil than in the bulk soil.
Abstract
The vine weevil, Othiorynchus sulcatus, is a serious pest in strawberries in Norway and biological control methods are needed to combat this pest. In this study, the rhizosphere competence of two cold active Norwegian fungal isolates (Metarhizium anisopliae isolate NCRI 250/02 and Beauveria bassiana NCRI 12/96) and the well known Ma43 originating from Austria were tested. This was done by estimating fungal concentrations in the bulk and rhizosphere soil surrounding the strawberry plant roots by counting colony forming unists (CFUs). The highest numbers of B. bassiana NCRI 12/96 CFUs were seen in the rhizosphere at 1.87x109 per liter soil 3 months after application. The highest numbers of M. anisopliae NCRI 250/02 CFUs were seen in the rhizosphere at 2.41x109 per liter soil 1 year after application. Numbers of CFUs for the M. ansiopliae Ma43 CFUs were generally lower than for the Norwegian isolates, but also for this isolate a higher fungal concentration was found in the rihzosphere soil than in the bulk soil.
Abstract
Neozygites floridana is a fungus in the order Entomophthorales that infects and kills the two-spotted spider mite, Tetranychus urticae. The fungus is therefore of interest in the biological control of T. urticae. To obtain information that might help in the use of this fungus under practical conditions in strawberries and cucumbers we have tried to answer the following questions in a series of studies: 1) When, and at what infection levels does N. floridana occur in T. urticae populations in field grown strawberries in Norway? 2) How does N. floridana survive harsh climatic conditions (i.e winter) in Norway? 3) Where do N. floridana infected T. urticae move and sporulate on a plant? 4) How can N. floridana be inoculated in augmentative microbial control of T. urticae? Results show that the N. floridana infection level varies considerably throughout a season. T. urticae killed by N. floridana was found to sporulate surprisingly early in the season (first observation March 18) and infection early in the season is important for a good control of T. urticae. N. floridana was observed to over-winter as hyphal bodies in hibernating T. urticae females throughout the winter. Cadavers with resting spores were found from October to the end of January only. Cadavers then probably disintegrated, and resting spores were left on leaves, soil, etc. In a bioassay where a Norwegian N. floridana isolate was tested for numbers and distance of spores thrown at three different temperatures relevant to Norwegian conditions (13o, 18o, 23o C), results show that the highest numbers of spores (1886 and 1733 per cadaver) were thrown at 13o and 18o compared to 23o C (1302 per cadaver). Spores were thrown at the same distance (up to about 6 mm) at all three temperatures. These results show that the fungus may be a promising agent at temperatures relevant for strawberry production in countries located in Northern areas. Our attempt to inoculate N. floridana artificially in a strawberry field and also in greenhouse cucumbers has not been successful yet, but we are working to improve the methods in a new project titled "BERRYSYS -A system approach to biocontrol in organic and integrated strawberry production".
Abstract
No abstract has been registered
Authors
Daniel Kwaku Addo Asante Igor A. Yakovlev Carl Gunnar Fossdal Gerrit Frantz Timmerhaus Jouni Partanen Øystein JohnsenAbstract
No abstract has been registered