Characterization of anti-channel catfish MHC class IIbeta monoclonal antibodies

This study characterizes four monoclonal antibodies (mAb) developed against the major histocompatibility complex (MHC) class II beta chain of the channel catfish, Ictalurus punctatus. Immunoprecipitations using catfish clonal B cells revealed that each of these mAbs immunoselected proteins of approximately 32 and 36 kD, which are of the appropriate sizes for MHC class II alpha and beta chains, respectively. Cell distribution studies using a fluorescence-activated cell sorter (FACS) combined with RT-PCR analyses demonstrated that MHC class II beta is expressed at a high density on catfish clonal macrophage, B and T cell lines, on alloantigen stimulated leukocytes, and on lipopolysaccharide-induced B-cell blasts. Collectively, these results demonstrate the potential importance of these antibodies as reagents in future studies dealing with the functional role of MHC class II molecules in immune recognition of self from non-self.     

Risks for infection of strawberry plants with an aerosolized inoculum of <Emphasis Type="Italic">Xanthomonas fragariae</Emphasis>

Xanthomonas fragariae is the causative agent of angular leaf spot of strawberry, a quarantine organism in plant propagation material in the European Union. Field experiments were conducted to assess the risks for infection of strawberry plants through dispersal of an aerosolized inoculum. In practice, pathogen aerosols can be formed during mowing of an infected crop or by water splashing on symptomatic plants during overhead irrigation or rain. In our experiments, aerosols were generated by spraying suspensions of X. fragariae with a density of 10⁸ cfu ml^?1 or water under pressure vertically up into the air. In strawberry plants (cv Elsanta) placed at 1.3, 5 and 10 m distance downwind from the spray boom, infections were found, as evidenced with a combination of dilution–plating and molecular techniques, but more frequently in plants wetted prior to inoculation than in plants kept dry. A logarithmic decrease in infection incidence was found with the distance to the inoculum source. Symptomatic plants were found up to 5 m distance from the inoculum source. No infected plants were found in plants placed 4 m upwind or treated with water. In glasshouse studies, it was shown that under conditions favorable for disease development, spray-inoculation of strawberry plants with estimated densities of X. fragariae as low as 2000 cfu per plant were able to cause symptoms both in cv Elsanta and cv Sonata. Results indicate that there is a considerable risk on infections of strawberry plants exposed to aerosolized inoculum.     

Production and use of maize seed for sowing in Bolívar,Ecuador

In the province of Bolívar in the Andean region 212 farmers, six salesmen and 14 technicians, involved in maize production, were interviewed. The majority of the farmers interviewed were small-holders; 64% of the farmers had a farm size of less than 4.5 ha. Maize is the most important crop and is often grown in association with beans. Most maize, 96%, is soft maize meant for human consumption. The cultivars grown are open pollinated ones. One cultivar, ‘Guagal’, was grown extensively. A few others, among which an improved version of Guagal were of some importance. In the production of maize the farmers consider damage due to insects, wind (lodging), diseases, drought and hail, the low prices for their surplus maize and the high costs of fertilizers, chemicals, sowing seed and labour as the most important constraints. The seed for sowing the next crop mainly came from seed kept from the last harvest. Farmers indicated that they select from the harvested ears the healthy looking larger ones. Kernel type also was a selection criterion. Selection for plant type in the field was rarely done. Of the farmers 71% stored the maize as kernels while 29% stored the seed kept on the ears. The storage was predominantly done somewhere in the house in plastic (56%) or cloth bags (14%), in a pile (13%), just on the floor (4%) or in cans (4%). Some farmers still had seed left from the last sowing and were willing to give a sample for testing. From 32 such samples the quality was assessed by INIAP, the Ecuadorean governmental research and breeding organisation. The samples were consistently of a low quality. Especially the vigour of the seedlings was poor and most of the seeds were infected or contaminated by fungi. In the region a few salesmen offer maize seed for sale of cultivar Guagal at prices affordable by the farmer. Of improved cultivars the prices were higher than most farmers are willing to pay. The technicians considered good seed quality and good maintenance of the cultivars effective methods in obtaining better yields. Many farmers do not have access to seed of INIAP and are not familiar with the improved cultivars.     

The natural control of the apple-grass aphid,Rhopalosiphum insertum,with remarks on the control of apple aphids in The Netherlands in general

In this paper the apple-grass aphid is stated to be the only aphid in the Netherlands that regularly hibernates in large quantities in commercial apple orchards. The possible reasons for this are discussed. Abiotic factors, especially rain, hail, wind and ice formation in early spring, are by far the most important in drastically reducing the numbers of fundatrices. Of the biotic factors, ladybird beetles in spring may be important. The apple-grass aphid parasite,Monoctonus cerasi, may reach high peaks of parasitism during some periods in the season; in comparison with abiotic factors, however, its effect does not seem to be very important. The life history of the parasite seems to be well adapted to that of its host. It is suggested that the winter wash against apple aphids might be omitted, with eventual application of a spring spray in certain circumstances. In most cases this spray will only be necessary if the rosy apple aphid is present. Samenvatting In deze publikatie wordt er de nadruk op gelegd dat de appel-grasluis,Rhopalosiphum insertum (Wlk.), de enige bladluis is die in appelboomgaarden die in produktie zijn regelmatig in groot aantal als ei overwintert. Hiervoor wordt een aantal redenen opgegeben, die samenhangen met verschillen in de levenswijze ten opzichte van de beide andere belangrijke bladluizen van appel, nl. de roze appelluis,Dysaphis plantaginea (Pass.), en de groene appeltakluis,Aphis pomi Geer. Uit Fig. 1, 2 en 3 blijkt, dat zowel de populatiedichtheid van de bladluis als de parasitering door de voornaamste parasiet,Monoctonus cerasi, in de loop van het seizoen vaak belangrijke schommelingen vertonen. De belangrijkste mortaliteitsoorzaken in het voorjaar zijn abiotische factoren zoals regen, wind, hagel en ijsvorming, die de bladluispopulaties in sterke mate kunnen decimeren. Van de biotische zijn hoofdzakelijk enkele soorten lieveheersbeestjes (Coccinellidae) van belang. De parasiet veroorzaakt in sommige perioden van het jaar weliswaar hoge parasiteringstoppen, maar haar effect is, vergeleken bij de invloed van de genoemde weersomstandigheden, weinig belangrijk. In verband met het besprokene lijkt een winterbespuiting tegen bladluizen op appel in het algemeen overbodig. Zo nodig kan in het voorjaar nog een bespuiting worden toegepast. Dit zal in het algemeen echter alleen noodzakelijk zijn als ook de roze appelluis optreedt, die door het vervormen van de vruchten veel schadelijker is dan de appel-grasluis.     

Over de invloed van de winter op de parasitering van de appelbloedluis,Eriosoma Lanigerum,door haar Parasiet Aphelinus Mali

Summary In the Netherlands the winter of 1955/56 was very severe and the winter of 1956/57 very mild. The woolly aphid, being much more susceptible to low temperatures than its parasite, these two winters had remarkable consequences for the parasitism in the summers, following these winters. This is demonstrated by the graphs of fig. 1 and 2 and by table 1.In 1956 almost all woolly aphids were killed by the severe frost in February. In the autumn a small infestation by the woolly aphid was observed and also a low rate of parasitism. As a result of the mild winter of 1956/57 relatively many aphids survived. At the beginning of season of 1957 the ratio parasites to aphids was also very low. Hence the influence of the first generation ofAphelinus mali in May was hardly observed (in the preceding years there was very marked parasitism in this period). In the summer of 1957, however, the parasite recovered completely with respect to its host, the woolly aphid, and in September a parasitism of 68% was reached.     

Epidemiology and Integrated Control of Potato Late Blight in Europe

Phytophthora infestans, the causal agent of late blight, is a major threat to potato production in northwestern Europe. Before 1980, the worldwide population of P. infestans outside Mexico appeared to be asexual and to consist of a single clonal lineage of A1 mating type characterized by a single genotype. It is widely believed that new strains migrated into Europe in 1976 and that this led to subsequent population changes including the introduction of the A2 mating type. The population characteristics of recently collected isolates in NW Europe show a diverse population including both mating types, sexual reproduction and oospores, although differences are observed between regions. Although it is difficult to find direct evidence that new strains are more aggressive, there are several indications from experiments and field epidemics that the aggressiveness of P. infestans has increased in the past 20?years. The relative importance of the different primary inoculum sources and specific measures for reducing their role, such as covering dumps with plastic and preventing seed tubers from becoming infected, is described for the different regions. In NW Europe, varieties with greater resistance tend not to be grown on a large scale. From the grower??s perspective, the savings in fungicide input that can be achieved with these varieties are not compensated by the higher (perceived) risk of blight. Fungicides play a crucial role in the integrated control of late blight. The spray strategies in NW Europe and a table of the specific attributes of the most important fungicides in Europe are presented. The development and use of decision support systems (DSSs) in NW Europe are described. In The Netherlands, it is estimated that almost 40% of potato growers use recommendations based on commercially available DSS. In the Nordic countries, a new DSS concept with a fixed 7-day spray interval and a variable dose rate is being tested. In the UK, commercially available DSSs are used for c. 8% of the area. The validity of Smith Periods for the new population of P. infestans in the UK is currently being evaluated.     

Synergy of cymoxanil and mancozeb when used to control potato late blight

Summary Synergism between fungicides could be used to reduce the application dosage. Synergism between cymoxanil and mancozeb was studied using potted potato plants under field conditions. In three experiments the preventive efficacy of the fungicides and fungicide mixtures in the treatments were studied using a bio-assay. Potato plants were sprayed with the fungicides or fungicide mixtures. Leaves were picked from the potato plants with regular intervals after fungicide application. The efficacy of the fungicides was studied in a bioassay by inoculating the leaves withPhytophthora infestans zoosporangia. The Abbot method was used to show synergistic effects of the cymoxanil/mancozeb mixtures tested. In two of three experiments synergy of the fungicide mixtures was found.