Effect of Cultivar Resistance and Haulm Killing Method on Tuber Infection by <Emphasis Type="Italic">Phytophthora infestans</Emphasis>

A series of field trials combining cultivars with different levels of resistance to Phythophtora infestans and different haulm killing methods was conducted in 1997, 1998 and 1999 to assess the contamination potential of the haulm. In addition, the frequency of tubers with late blight was assessed after harvest and storage, combining effects of pretreatment infection, infection by the haulm at harvest and the development of the disease during storage. Haulm killing was performed by diquat (200, 400, 600 g a.i. ha^-1), half cutting of the haulm in combination with diquat (100, 200, 300 g a.i. ha^-1) or full cutting of the haulm. In those treatments where haulm killing was performed purely chemically the haulm remnants’ contamination potential tended to increase at reduced doses. Full mechanical destruction gave as low a contamination potential as application of the full dose of chemical haulm killer. However, there were no consistent differences between the haulm killing treatments in the frequency of blighted tubers after harvest and storage. This indicates that the input of chemical haulm killers may be reduced. There was a large difference between years in tuber blight after harvest and storage, which confirms that climatic factors are of major importance for tuber infection. The large difference found between the cultivars in the frequency of tuber blight indicates that tuber resistance should be an important part of integrated late blight disease management.     

Isolation and characterization of Streptomyces species from potato common scab lesions in Norway

The present survey was conducted to isolate and characterize Streptomyces species from common scab lesions of potato in Norway. Bacteria were isolated from scab lesions on tubers sampled in two consecutive years at different locations in Norway spanning ～1400 km from south to north. In total, 957 independent isolations from individual tubers were performed, with 223 putative pathogenic isolates obtained from 29 different potato cultivars and 130 different fields. Streptomyces europaeiscabiei was the most abundant species isolated from common scab lesions (69%), while 31% of the isolates obtained were S. turgidiscabies. Streptomyces scabies was not found. Pathogenicity of selected Streptomyces isolates was tested on potato. The ability of the bacterial isolates to infect potato was consistent with the presence of the txtAB operon. The results revealed no pattern in geographical distribution of S. europaeiscabiei and S. turgidiscabies; both could be found in the same field and even the same lesion. Four different pathogenicity island (PAI) genotypes were detected amongst the txtAB positive isolates: nec1+/tomA+, nec1–/tomA+, nec1+/tomA? and nec1?/tomA?. The current findings demonstrate that there is genetic variability within species and that the species are not spread solely by clonal expansion. This is thought to be the most comprehensive survey of Streptomyces species that cause common scab of potato in a European country.     

Fungal pathogens in Norwegian lettuce fields

Abstract

Norwegian field production of lettuce has increased considerably since the early 1990s. Disease problems rarely required fungicide applications before 1996, when lettuce downy mildew (Bremia lactucae) caused severe losses. From 2002 to 2004, surveys were conducted to identify fungal diseases in Buskerud, Vestfold and Østfold counties in the south-east and Rogaland County in the south-west, representing the main lettuce production regions of Norway. The distribution and incidence of B. lactucae was highly variable, but this pathogen was the most important due to the destructive nature of uncontrolled epidemics. Septoria lactucae caused severe damage, but was found in only one field. Sclerotinia sclerotiorum was the most widespread pathogen, found in 32% of the fields, but usually affecting less than 10% of the plants. Pythium tracheiphilum was reported from 33% of the fields in south-east Norway, but was not found in the south-west. Disease incidence was usually less than 5%, and a disease incidence of more than 10% was reported in one field only. Other pathogens of potential economic importance in Norwegian lettuce fields are Alternaria spp., Botrytis cinerea and Rhizoctonia solani, although they were sporadically distributed in relatively few fields in this survey.     

Impact of Diurnal Periodicity, Temperature, and Light on Sporulation of Bremia lactucae

ABSTRACT We evaluated direct and interactive effects of light quality and intensity, temperature and light, diurnal rhythms, and timing of high relative humidity during long day lengths on sporulation of Bremia lactucae, the causal agent of lettuce downy mildew, using inoculated lettuce seedlings and detached cotyledons. Suppression of sporulation by light was strongly dependent upon temperature and there was little suppression at 相似文献   

Nitrogen distribution as affected by stocking density in a combined production system of energy crops and free-range pigs

Free-range pig production is typically associated with high risks of nitrogen (N) leaching due to the pigs excretory behaviour creating nitrogen ‘hotspots’ and rooting behaviour destroying the grass sward. This challenge is reinforced at high animal densities causing high nitrogen deposition. A combined production of pigs and perennial energy crops was hypothesized to benefit the environment because crops like miscanthus (Miscanthus), willow (Salix) and poplar (Populus) may persist despite pig rooting, take up nutrients and thereby minimise N-losses. Thus, the aim was to assess the risk of nitrate leaching by investigating the distribution of soil mineral N as influenced by stocking density in a system with zones of perennial energy crops and grass. For each of two seasons 36 growing pigs with an initial mean live weight of 55 kg (spring) and 48 kg (autumn), respectively, were separated into 6 paddocks of two stocking densities (117 and 367 m² pig^?1), respectively. Soil mineral N was measured in 0–25 and 25–75 cm depth at three occasions. N balances showed that N inputs exceeded N outputs by 626 and 185 kg N ha^?1 for high and low stocking density. The pigs caused an uneven distribution of mineral N across the paddocks with highest contents in zones with willow & poplar. Stocking density had a significant effect on soil mineral N. Immediately after the second batch of pigs, average mineral N in the 0–75 cm soil layer was on average 227 and 83 kg N ha^?1 at high and low stocking density, respectively. During winter period with no pigs, soil mineral N content in the 0–75 cm soil layer was reduced by almost 100 kg N ha^?1 in paddocks with high stocking density against only 4 kg in paddocks with low stocking density. It is concluded that risk of elevated nitrate leaching compared to other cropping systems was low at the low stocking density, which therefore represents a promising pathway for a combined production of energy crops and free-range pigs.     

Effect of nose ringing and stocking rate of pregnant and lactating outdoor sows on exploratory behaviour, grass cover and nutrient loss potential

Nose ringing of outdoor sows is practiced to reduce grass sward damage for environmental reasons but conflicts with natural behaviour considerations. We investigated effects of ringing pregnant and lactating outdoor sows on foraging and explorative behaviour, grass cover and nutrient deposition. The experiment included both ringed and unringed sows. For unringed sows the paddocks were either used continuously throughout the experiment or divided into two and sows were moved half way through the experimental period leaving the first used paddock for regrowth. Ringing did not prevent the sow's rooting, but rooting was less pronounced, when sows were ringed. On average, ringing increased grass cover from 14% to 38% and from 64% to 81% in paddocks with pregnant and lactating sows, respectively. In paddocks with unringed sows kept at a double density and followed by a resting period, the grass cover in autumn was restored to a high degree in paddocks with pregnant sows. In lactating sow paddocks the level of inorganic N was high but with no significant relation to extent of grass cover. In pregnant sow paddocks the soil inorganic N content was significantly reduced by increased grass cover and at 60% grass cover soil inorganic N content was at a low level. From the experiment it was evident that although ringing did have a positive environmental effect, it was not the main factor influencing potential losses. Management choices in terms of feeding, animal density and nutrient distribution are considered to be at least as important.     

Crop content in nutrient-restricted versus non-restricted organic laying hens with access to different forage vegetations

1. The purpose of this study was to evaluate how feed intake of organic layers varies according to type of forage vegetation available when hens are fed a normal concentrate for organic layers or a nutrient-restricted diet with whole wheat and oyster shells, assuming that the nutrient-restricted diet would reflect the capacity of the hens to forage. 2. Two 23-d experiments were arranged with chicken runs in a 2 x 2 factorial design with two types of complementary feed (concentrate with 184 g/kg dry matter (DM) crude protein vs whole wheat with 120 g/kg DM crude protein) and two types of forage vegetation (grass/clover vs a mixture of forbs in experiment 1 and grass/clover vs chicory in experiment 2): each experiment was carried out in three replications. 3. Twice during each experiment two hens from each run were slaughtered - two in the evening and two the following morning. Subsequently, the birds' crops were removed. Crop content was separated into 8 fractions. 4. For most feed items crop content was found to be significantly higher in the evening than in the morning. 5. Complementary feed significantly influenced the content of several feed items in the crop. In both experiments wheat-fed hens had a significantly higher amount of soil in the crops and a significantly lower amount of weed seeds compared to the concentrate-fed hens. Plant material and grit stone were significantly more abundant in wheat-fed hens only in experiment 2 and numerically more abundant in experiment 1, whereas the amount of oyster shells was significantly higher in wheat-fed hens in experiment 1 and numerically higher in experiment 2. 6. Type of forage itself only significantly influenced the amount of soil in the crops in experiment 1 and amount of seeds in experiment 2, since more soil was found in hens foraging on the mixed forbs and more seeds were found in the hens foraging on the chicory plots, respectively.     

Short-term effects on productivity and egg quality in nutrient-restricted versus non-restricted organic layers with access to different forage crops

Abstract

Two experiments were conducted to study the effects of different forage crops on productivity and some egg quality parameters of small flocks of organic laying hens fed whole wheat or concentrates. Each experiment was carried out in a split plot design with two different forage crops and two types of supplementary feed (typical concentrate for organic layers versus whole wheat) with three replications. In the first experiment the tested forage crops were of a well-established grass/clover and a mixture of forbs (Fagopyrum esculentum, Phacelia tanacetifolia and Linum usitatissimum). In the second experiment the tested forage crops were a well-established grass/clover and chicory (Cichorium intybus cv. Grassland Puna). The results on productivity and egg quality suggest that laying hens consume large amounts of foraging material when accessible. In nutrient restricted hens (wheat-fed) the forage may yield a substantial contribution to the requirements of amino acids and metabolizable energy although productivity parameters and measurements on dry matter in albumen showed that wheat-fed hens, on a short-term basis, were not able to fully compensate for the lack of protein and amino acids by increased foraging. Of the forage crops investigated especially chicory seems to contribute to the nutrition of the hens. Measurements on eggshell parameters showed that oyster shells together with foraging material were sufficient to meet the hens’ calcium requirements. Yolk colour clearly revealed that laying hens consume large quantities of green fodder irrespective of the type of supplementary feed. Yolk colour from hens with access to chicory tended to be darker, of a redder and less yellow hue compared with grass/clover fed hens, which is considered a positive quality.     

Phenotypic variation in Nordic populations of Phytophthora infestans in 2003

A total of 743 single-lesion isolates of Phytophthora infestans were collected in summer 2003 from Denmark, Finland, Norway and Sweden. Most of the isolates were tested for mating type, and subsets were tested for sensitivity to fungicides and virulence (host specific pathogenicity). Approximately 60% of the isolates were A1 mating type in each country. Both mating types were present in 40% of the fields where more than one isolate was tested, indicating strong potential for sexual reproduction. The proportion of metalaxyl-resistant isolates dropped to under 15% from the 60% observed in the early 1990s in Norway and Finland, possibly due to lower selection pressure because of decreased use of metalaxyl. Propamocarb-HCl sensitivity remained unchanged in the Nordic countries compared to the situation in 1997–2000 in Finland. Four isolates collected from Finland and Sweden were able to sporulate in the presence of this fungicide at a concentration of 1000 mg L⁻¹. In Norway and Finland the frequencies of virulence factors and pathotypes remained nearly unchanged since the 1990s, but the mean number of virulence factors per isolate increased from 5·6 to 6·3. In Denmark and Sweden virulence factors 2 and especially 6 were more common than in Norway and Finland. In addition, in the Swedish population the frequencies of pathotypes were quite even while in other countries pathotype 1,3,4,7,10,11 was most prevalent.     

PCR‐based identification of Pythium spp. causing cavity spot in carrots and sensitive detection in soil samples

On the basis of ITS sequences PCR primers were designed for the identification of the five Pythium species found to be most important for the development of carrot cavity spot in Norway: P. intermedium, P. sulcatum, P. sylvaticum, P. violae and P. ‘vipa’. The P. ‘vipa’ isolates had a unique ITS sequence, differed morphologically from all other Pythium isolates, and thus probably represent a new species. The PCR primers were species‐specific with no cross‐reaction to other Pythium species or to fungal isolates from carrot tested. The detection limits varied for the different primer pairs. The two most sensitive assays allowed detection of as little as 5 fg DNA. All five Pythium species could be detected in lesions from diseased carrots. Weak positive signals were obtained from some carrot samples without symptoms. PCR assays allowed detection of pathogens in soil. In samples of soil known to produce cavity spots on cropped carrots, strong signals were obtained. In several soil samples more than one of the five Pythium species could be detected. The utilization of this diagnostic PCR assay in analysis of field soil and carrot tissue might in the future be exploited to reduce the incidence of this serious carrot disease.